Digest for sci.electronics.repair@googlegroups.com - 5 updates in 3 topics

9:41 AM Penedão 0 comments
bruce bowser <bruce2bowser@gmail.com>: Oct 30 03:49PM -0700

Peter,
solar and wind are growing, the rest are dead (or they just don't know it, yet)
Jeff Layman <Jeff@invalid.invalid>: Oct 31 08:46AM

On 30/10/2022 22:49, bruce bowser wrote:
> Peter,
> solar and wind are growing, the rest are dead (or they just don't know it, yet)
 
Unless battery storage is improved and expanded exponentially, that
would only work with a world-wide grid. Wind power is not predictable or
reliable, and in winter when you most need it you can get cols when no
wind blows for days. So you have a world-wide grid to link vast solar
arrays on both sides of the globe to ensure that power is available
everywhere day and night.
 
It would be similar to the gas pipeline "grid" we have at present in
Europe. That's working well with Russian gas, isn't it?...
 
--
 
Jeff
"Peter W." <peterwieck33@gmail.com>: Oct 31 04:09AM -0700

On Monday, October 31, 2022 at 4:47:01 AM UTC-4, Jeff Layman wrote:
> On 30/10/2022 22:49, bruce bowser wrote:
> > Peter,
> > solar and wind are growing, the rest are dead (or they just don't know it, yet)
 
Against stupidity the very gods themselves contend in vain.
 
Schiller
 
Both wind and solar require pretty large footprints to make power at utility quantities.
 
Wind requires roughly one acre per megawatt - this assuming that the other open land required for clearances may also be used for farming or other similar purposes - just not housing, public buildings or schools.
A solar farm requires between five (5) and ten (10) acres per megawatt depending on location. Use 7.5.
Nuclear power requires very roughly 10% of the footprint of solar, but the plants produce far more power per acre, so the footprints for a large nuclear plant seem large - but they are not.
There is enough nuclear fuel on the planet *right now* to last very nearly 1,000 years at present levels of consumption. Put another way, present technology uses about 9.5% of the energy in the fuel. Using presently available processes and technologies, that may be extended to well over 50%.
There are over 1,500 boreholes in Nevada, alone that will be radioactive for the next 30,000 years or so. One (1) of the larger ones is capable of holding all the nuclear waste generated from all nuclear power plants world-wide. There are 1,500 of them, once again. In Nevada, alone. Once again.
93 US-based nuclear plants produce 19% of the total power used in the US.
Electricity consumption in the United States totaled 3,930 terawatt hours in 2021. Of that, 746.7 terawatt-hours were generated by nuclear plants.
One (1) Terawatt = One Million (1,000,000) megawatts.
So, vastly oversimplified, the standing capacity for power generation must be 1/24th of 1/365th of total consumption.
That comes to 85,240 MW for nuclear.
That comes to 448,639 MW entirely.
490 nuclear plants using present-day technology would do it, at an average of 100 acres each, or 49,000 acres.
That comes to 3,364,726 acres for solar.
That comes to 4.3 Rhode Islands. Very nearly four times that in actual practice, as last I looked the sun does not shine at night, weather still happens, and above the tropics, seasonal variations are an issue.
 
As to wind, those locations where it is practical are limited such that it is doubtful that, for instance, whether any of several interior US states would have sufficient capacity, and areas where there are regular high winds, deep cold or other conditions would also be limited.
 
Any nuclear ship or submarine will demonstrate the portability of nuclear power.
 
Peter Wieck
Melrose Park, PA
James Yuan <unionwellchina@gmail.com>: Oct 31 12:56AM -0700

在 2009年4月28日星期二 UTC+8 06:52:05，<Dave Plowman (News)> 写道：
> *I used up all my sick days so I called in dead
> Dave Plowman da...@davenoise.co.uk London SW
> To e-mail, change noise into sound.
 
Deepmaterial is reactive hot melt pressure sensitive adhesive manufacturer and supplier, manufacturing one component epoxy underfill adhesives, hot melt adhesives glue, uv curing adhesives,high refractive index optical adhesive, magnet bonding adhesives, best top waterproof structural adhesive glue for plastic to metal and glass, electronic adhesives glue for electric motor and micro motors in home appliance.
For more visit:
https://www.epoxyadhesiveglue.com/
https://www.deepmaterialcn.com/
James Yuan <unionwellchina@gmail.com>: Oct 31 12:50AM -0700

在 2020年4月15日星期三 UTC+8 12:07:42，<Mike S> 写道：
> please be aware that there are certain types - including polyethylene
> and polypropylene sheet - that it will not adhere to.
 
> https://www.acplasticsinc.com/informationcenter/r/the-best-adhesives-for-plastics
 
Deepmaterial is reactive hot melt pressure sensitive adhesive manufacturer and supplier, manufacturing one component epoxy underfill adhesives, hot melt adhesives glue, uv curing adhesives,high refractive index optical adhesive, magnet bonding adhesives, best top waterproof structural adhesive glue for plastic to metal and glass, electronic adhesives glue for electric motor and micro motors in home appliance.
For more visit:
https://www.epoxyadhesiveglue.com/
https://www.deepmaterialcn.com/
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Digest for sci.electronics.repair@googlegroups.com - 1 update in 1 topic

9:40 AM Penedão 0 comments
Cursitor Doom <cd@notformail.com>: Oct 26 10:18PM +0100

On Wed, 26 Oct 2022 08:57:06 -0700 (PDT), "Peter W."
>b) Most (not all) hobbyists are not limited by cost constraints for a few parts. So, a US$20-or-equivalent investment to save a valuable item is not outrageous.
>c) Most of the effort in repairs is 'getting to it' - the taking-apart, the testing, documenting, and then reassembly.
>d) The actual repairs take very little time.
 
"The actual repairs take very little time."
 
If you only knew the irony of that statement when the task is
completeed by someone with my eyesight and fine motor skills.
 
>As to soldering and technique - time and repetition will give you more confidence.
 
No it won't. I've been doing this for more than 50 years and I'm still
every bit as shit at it as I was half a century ago. I have not
improved one iota and only a damn fool would believe the future's
going to be any better than the past with a skill set like mine.
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Digest for sci.electronics.repair@googlegroups.com - 14 updates in 1 topic

9:40 AM Penedão 0 comments
three_jeeps <jjhudak@gmail.com>: Oct 25 10:45AM -0700

On Monday, October 24, 2022 at 2:12:12 PM UTC-4, Peter W. wrote:
 
> I kinda-sorta think that will do it. KISS and all that.
> Peter Wieck
> Melrose Park, PA
 
Ditto.....I was going to suggest this but some ppl want to find *the* problem. For *vintage* stuff, it makes no sense to me, Replace all the caps, check all resistors. Having a solid power supply is critical for the rest of the unit to work properly, so why screw around with replacing only one bad component? As long as you got it apart.....Do you really want to revisit this later when another cap dies?
Cursitor Doom <cd@notformail.com>: Oct 25 07:33PM +0100

Here we go, gentlemen, the finished "repair" on the PSU board:
 
Before (the faulty RIFAs are arrowed since they're a bit hard to spot)
https://disk.yandex.com/i/9VID9SDCNLoxQw
 
After (the new replacements are not arrowed, since they're blindingly
obvious)
https://disk.yandex.com/i/uHJW9u33lWACVQ
 
 
It's just awful, isn't it?
Jeff Liebermann <jeffl@cruzio.com>: Oct 25 12:42PM -0700

On Tue, 25 Oct 2022 19:33:00 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 
>obvious)
>https://disk.yandex.com/i/uHJW9u33lWACVQ
 
>It's just awful, isn't it?
 
I've done worse. I don't like the exposed hot wires, but since you're
the only person likely to be working on the scope, it's probably an
acceptable risk.
 
I suggest you tack the capacitors to the PCB with a little REMOVABLE
glue, such as hot melt glue or non-acetic-acid RTV.
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
JC <Chipbee40_SpamNo@yahoo.com>: Oct 25 03:43PM -0400

Cursitor Doom wrote:
> obvious)
> https://disk.yandex.com/i/uHJW9u33lWACVQ
 
> It's just awful, isn't it?
 
Probably won't fit back in the scope cos of the IEC filter.
Tons of info out there on this power supply and how to fix:
 
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/150/
Cursitor Doom <cd@notformail.com>: Oct 25 09:38PM +0100

On Tue, 25 Oct 2022 12:42:51 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
 
>I've done worse. I don't like the exposed hot wires, but since you're
>the only person likely to be working on the scope, it's probably an
>acceptable risk.
 
Thanks, Jeff, I thought you'd tear me a new arsehole!
 
>I suggest you tack the capacitors to the PCB with a little REMOVABLE
>glue, such as hot melt glue or non-acetic-acid RTV.
 
In an ideal world and all that. Sadly, we both know that's not going
to happen, Jeff. :-(
Cursitor Doom <cd@notformail.com>: Oct 25 09:39PM +0100

On Tue, 25 Oct 2022 15:43:14 -0400, JC <Chipbee40_SpamNo@yahoo.com>
wrote:
 
>> https://disk.yandex.com/i/uHJW9u33lWACVQ
 
>> It's just awful, isn't it?
 
>Probably won't fit back in the scope cos of the IEC filter.
 
It does actually fit back in again - *just* about.
 
>Tons of info out there on this power supply and how to fix:
 
>https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/150/
 
Many thanks for that indeed.
Cursitor Doom <cd@notformail.com>: Oct 25 09:54PM +0100

>for embarrassing field failures after 20+yrs.
 
>X2 caps are desiged for 'impedance-limited' applications and
>are tested at around 1KVAC/1500VDC.
 
Do you know why these caps usually have their self-resonant frequency
marked on the side of them? That's always puzzled me.
three_jeeps <jjhudak@gmail.com>: Oct 25 02:19PM -0700

On Saturday, October 22, 2022 at 2:34:59 PM UTC-4, Cursitor Doom wrote:
> >Melrose Park, P
> These are X2 caps and supposed to fail short. However, for whatever
> reason, they both failed open.
 
Fail short...really? Why would you want a cap that is across the supply line to fail short? Just to make sure the fuse blows?
It is my understanding that X and Y capacitors experience line spikes, and will endure multiple small breakdowns over the years as a result of this stress. They fail open because local heating caused by a microscopic dielectric breakdown results in polypropylene melting, which seals off the "edge" of the breakdown.
Is this not correct??
Cursitor Doom <cd@notformail.com>: Oct 25 10:38PM +0100

On Tue, 25 Oct 2022 14:19:38 -0700 (PDT), three_jeeps
 
>Fail short...really? Why would you want a cap that is across the supply line to fail short? Just to make sure the fuse blows?
>It is my understanding that X and Y capacitors experience line spikes, and will endure multiple small breakdowns over the years as a result of this stress. They fail open because local heating caused by a microscopic dielectric breakdown results in polypropylene melting, which seals off the "edge" of the breakdown.
>Is this not correct??
 
No idea if that's the failure mechanism or not. However, if you read
my orginal remark, I did say they are *supposed* to fail short, which
makes pretty clear that was the intention of the manufacturer even if
they were not successful in many instances.
Rayner Lucas <usenet202101@magic-cookie.co.ukNOSPAMPLEASE>: Oct 26 01:04AM +0100

In article <4696384c-8b39-4bae-a924-81096d9b3da0n@googlegroups.com>,
pallison49@gmail.com says...
 
> ** Rifa PME271 X2 caps are still made and widely available.
> Strangely they are also the most expensive X2 caps on offer for no
> good reason.
 
I got a handful of brand new PME271 Y caps a few years ago, for reasons
that I'm sure can't possibly have been good ones. All of them have
developed a couple of small cracks in the casing, just from sitting
unused in a parts box.
 
So if anyone was wondering if they'd fixed the defects in the design at
any point in the last 40+ years, apparently not.
 
> IME Rifa X2s are notorious for catching fire and filling the room with
> acrid smoke. Happened twice, right in front of me, first case was a
> room heater and the second with a portable TV.
 
Yep, they're a menace all right. These days I pre-emptively check any
mains-powered electronics from the 80s and 90s for them, which
thankfully meant I got them out of my Tek 2445A before they popped. Wish
I'd been more alert with the 2235A; I spent ages cleaning sticky brown
crud out of the crevices of that one.
 
And then there was the HP spectrum analyser where I thought I'd saved
myself a heap of trouble by extracting all eight(!) Rifa capacitors from
its power supply. Plugged it in, and half an hour later a thick cloud of
truly foul phenolic smoke poured out. Opened it up to find that it had
blown part of the case off its power inlet. Turns out that Schaffner
filtered power inlets can *also* contain Rifa (or very similar) caps,
concealed inside a metal casing and potting compound just to add extra
force and noxious smells to the eventual and inevitable explosion.
 
I'm pretty sure anyone who works on older electronics eventually
develops their very own rant about these accursed objects.
 
Rayner
legg <legg@nospam.magma.ca>: Oct 26 08:34AM -0400

On Tue, 25 Oct 2022 19:33:00 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 
>obvious)
>https://disk.yandex.com/i/uHJW9u33lWACVQ
 
>It's just awful, isn't it?
 
You could probably have leadformed the new parts to suit.
 
My guess is you just prefered to solder from the comp
side.
 
RL
Cursitor Doom <cd@notformail.com>: Oct 26 04:15PM +0100


>My guess is you just prefered to solder from the comp
>side.
 
>RL
 
It's really not my thing. When people say, "Just recap anything
suspect" and there might be fewer than half a dozen to do, the
prospect still fills me with horror. If they only knew how ironic the
"Just" bit strikes me in suggestions like that.
"Peter W." <peterwieck33@gmail.com>: Oct 26 08:57AM -0700

> suspect" and there might be fewer than half a dozen to do, the
> prospect still fills me with horror. If they only knew how ironic the
> "Just" bit strikes me in suggestions like that.
 
The problem with vintage equipment, however well designed and well built, is that parts within it age. Typically, items that are approaching, or exceeding 30 years old will have some marginal parts within. Further, if those parts are 'common' as in "many of them", if one fails the others will not be far behind. Some truisms:
 
a) As in the Holland America commercials - Time is a precious commodity.
b) Most (not all) hobbyists are not limited by cost constraints for a few parts. So, a US$20-or-equivalent investment to save a valuable item is not outrageous.
c) Most of the effort in repairs is 'getting to it' - the taking-apart, the testing, documenting, and then reassembly.
d) The actual repairs take very little time.
 
So, when whatever the device might be, when it is taken apart, *THEN* is the time to refurbish the entirety to the greatest extent possible - to avoid having to repeat the process if nothing else. Analogy: the engine in your vehicle spins one (1) bearing. You would replace _ALL_ of the bearings, as the incremental cost of the additional bearings against the cost of the tear-down is tiny, and the rewards significant. There is a school of thought that suggests that repairs are made only to the minimum necessary. Subscribers to this theory are the ones that one sees stranded on the side of the road in a blinding snowstorm.
 
Your power-supply went through a traumatic event - and it is supplying a complex and expensive piece of equipment. Consider it in that light.
 
As to soldering and technique - time and repetition will give you more confidence.
 
Peter Wieck
Melrose Park, PA
"Peter W." <peterwieck33@gmail.com>: Oct 26 08:57AM -0700

That would be Viking....
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Digest for sci.electronics.repair@googlegroups.com - 16 updates in 1 topic

9:40 AM Penedão 0 comments
Charles Lucas <charlesandmilly@gmail.com>: Oct 24 10:12AM -0700

Hi, everyone (including the original poster).
 
When the power supply unit fails, there can be a basic myriad of possible problems
and/or failed components.
 
Here are some things to look for:
 
Current limiting resistors, rectifier diodes, transformers, transistors,
caps., filters, coils, etc... Shorts and opens are common problems. Look
for bad connections, cold solders, etc... Lots to check for to "pin in down".
Especially with older devices. Since it is an analog device (as was said),
it is assumed the equipment is old, so we have to go to the old school
way of checking everything, looking for key things, in order to come up
with some accurate diagnosis.
 
Good luck and have a great day.
 
Charles Lucas
three_jeeps <jjhudak@gmail.com>: Oct 24 10:29AM -0700

On Sunday, October 23, 2022 at 8:14:05 PM UTC-4, Jeff Liebermann wrote:
> PO Box 272 http://www.LearnByDestroying.com
> Ben Lomond CA 95005-0272
> Skype: JeffLiebermann AE6KS 831-336-2558
 
I know about the RIFA caps exploding - thanks for the interesting video tho.
What is the recommended replacement type? (assuming they can physically fit into the same space on the board)
I have a few vintage Tek scopes that I should do some preventative maintenance work on....
J
Jeff Liebermann <jeffl@cruzio.com>: Oct 24 10:35AM -0700

>while seals lasted. The outer sealing body tended to shrink and crack
>with age, allowing ingress of air and moisture, compromising
>performance. They are no longer made.
 
When I test RIFA capacitors with the Megger, I sometimes see
capacitors the show some leakage for maybe 250 msec and then recover.
I've been assuming that this demonstrates that self healing is
function. Known good capacitors don't do that. Since testing
required removing the capacitor from the PCB, I just replace any
capacitor that shows temporary leakage. (i.e. better safe than
sorry).
 
This video shows what might be two self healing RIFA capacitors in
action. Watch the current on the display:
"40 Year Old Rifa Capacitors High Voltage Leakage Testing"
<https://www.youtube.com/watch?v=m1nDrunJ1SE> (3:09)
The effect is more visible with a panel meter than with a digital
readout (except when the meter is moving because I'm turning the crank
on the Megger).
 
>of internal faults, but in extreme cases, you still get thermal
>runaway, as the faulting area expands and eats away at succesive
>layers of the wrapped structure.
 
I haven't bothered to perform a post mortem on a RIFA capacitor. I
have several suitable microscopes and would expect to find holed in
the dielectric (paper or plastic) and the metalization. The RIVA caps
that failed have warped, cracked, melted, or crumbled outer plastic
cases. For meaningful microscopy, I would need an old RIFA capacitor
in an intact case.
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
Jeff Liebermann <jeffl@cruzio.com>: Oct 24 11:10AM -0700

On Mon, 24 Oct 2022 10:29:52 -0700 (PDT), three_jeeps
>What is the recommended replacement type? (assuming they can physically fit into the same space on the board)
>I have a few vintage Tek scopes that I should do some preventative maintenance work on....
>J
 
"RIFA - Replacement Choices"
<https://www.eevblog.com/forum/beginners/rifa-replacement-choices/>
 
Kemet bought RIFA. My older Tek scopes survive 30 to 40 years and
usually blow electroltyics before RIFA caps. Rather than experiment,
I simply bought the same value/voltage X2 "safety" caps from Kemet
(via Mouser or Digikey):
<https://www.kemet.com/en/us/capacitors/film/safety.html?40=133>
 
I wasn't very careful when I ordered replacement caps many years ago.
I think I ordered "metalized paper", which in retrospect, was not the
best choice. Going down the list of dielectrics, only "metalized
paper" and "metalized polypropylene" are available for "safety" caps.
Kemet is recommending their R53 X2 caps with "metalized polypropylene
film" dielectric.

<https://www.mouser.com/new/kemet-electronics/kemet-miniature-emi-suppression-capacitors/>
<https://www.digikey.com/en/product-highlight/k/kemet/r53-film-capacitors>
 
X2 is for "line to line" filtering while Y2 is for "line to ground"
filtering.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
"Peter W." <peterwieck33@gmail.com>: Oct 24 11:12AM -0700

OK.
What is known:
 
a) Scope is blowing mains fuses.
b) RIFA -branded caps blew up.
c) The power-supply board was affected.
 
Suggestion:
1) Remove the power-supply board.
2) Replace all, repeat: ALL the capacitors on that board of any nature, type or style with the correct (but modern) replacement type.
3) Check each other component on the board. Diodes, regulators, transistors, whatever.
4) Replace any that are either bad or the slightest bit questionable.
5) Replace board - carefully (now might be an opportunity for a DBT to 'do its thing' - but a metered Variac would be better).
 
I kinda-sorta think that will do it. KISS and all that.
 
Peter Wieck
Melrose Park, PA
Jeff Liebermann <jeffl@cruzio.com>: Oct 24 12:04PM -0700

On Sun, 23 Oct 2022 11:16:19 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
(chomp...)
 
When in doubt, replace everything.
I was wondering if someone sells a recap kit for the Tek 2465. Yep:
<https://www.ebay.com/itm/313637931679>
It includes some RIFA -> Kemet replacement caps.
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
Cursitor Doom <cd@notformail.com>: Oct 24 10:10PM +0100

On Mon, 24 Oct 2022 11:10:12 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
><https://www.digikey.com/en/product-highlight/k/kemet/r53-film-capacitors>
 
>X2 is for "line to line" filtering while Y2 is for "line to ground"
>filtering.
 
Jeff, remind me to post a picture of the cap replacement I've carried
out. You'll be both horrified and astounded. If I had more time I'd
post it now, but it'll have to wait for the time being..
Cursitor Doom <cd@notformail.com>: Oct 24 10:17PM +0100

On Mon, 24 Oct 2022 11:12:09 -0700 (PDT), "Peter W."
>4) Replace any that are either bad or the slightest bit questionable.
>5) Replace board - carefully (now might be an opportunity for a DBT to 'do its thing' - but a metered Variac would be better).
 
>I kinda-sorta think that will do it. KISS and all that.
 
I do have a metered variac, so plan to use that in series with DBT
current limiting, as the bulb can react to sudden over-current much
more quickly than I can. I'll slowly bring the variac up whilst
checking for anything getting warm on the board. That's the best I can
manage as I'm no tech repairer; haven't got the necessary fine motor
skills, I'm afraid.
Jeff Liebermann <jeffl@cruzio.com>: Oct 24 04:52PM -0700

On Mon, 24 Oct 2022 22:17:57 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 
>I'm no tech repairer; haven't got the necessary fine motor
>skills, I'm afraid.
 
Not a problem. Let a hand soldering robot do the precision work.
Something like this soldering robot:
<https://www.promationusa.com/9101>
More:
<https://www.promationusa.com/robotic-soldering-glance>
and even more:
<https://www.google.com/search?q=hand+soldering+robot&tbm=isch>
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
Phil Allison <pallison49@gmail.com>: Oct 24 05:21PM -0700

legg wrote:
------------------
 
> >>Plenty are found open or with low values after long times in service.
> >>X2 dropping caps used in smoke alarms regularly fail open.
 
> >>But those Rifa ones love to smoke and burn.
 
==================================================
> while seals lasted. The outer sealing body tended to shrink and crack
> with age, allowing ingress of air and moisture, compromising
> performance. They are no longer made.
 
** Rifa PME271 X2 caps are still made and widely available.
Strangely they are also the most expensive X2 caps on offer for no good reason.
Described as being of "metalised , impregnated paper " construction.
Rifa also claim to be the only supplier .

Other makers, dozens of them, use metalised polyester or polypropylene films as used in DC rated caps - but with one big difference.
X2 types are double wound = a technique that creates two caps in series.
 
Such caps are immune from *corona discharge* occurring in tiny air pockets trapped inside the cap as it it being wound.
They are still vulnerable to spike voltages of a few kV which eat away at metalisation and reduce cap value over time.
 
IME Rifa X2s are notorious for catching fire and filling the room with acrid smoke.
Happened twice, right in front of me, first case was a room heater and the second with a portable TV.
 
When used for suppression in triac dimming equipment, they invariably fail early too.
Bad news.
 
..... Phil
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Oct 24 08:38PM -0400

Cursitor Doom wrote:
> Thanks,
 
> CD.
 
> https://disk.yandex.com/i/UhxATIy-6Y0LIA
 
Yikes. When a fuse blows, you replace it *once*. If it blows again, it
ain't the fuse or a line transient.
 
Start with a DMM and check for shorted diodes in the input bridge and
then for a shorted filter cap at its output. (The schematic is more or
less completely illegible, or I'd give the ref des.)
 
Next most likely is a switch FET.
 
Cheers
 
Phil Hobbs
(proud owner of a 2467 that he almost never uses)
 
 
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
 
http://electrooptical.net
http://hobbs-eo.com
Cursitor Doom <cd@notformail.com>: Oct 25 08:33AM +0100

On Mon, 24 Oct 2022 20:38:01 -0400, Phil Hobbs
 
>> https://disk.yandex.com/i/UhxATIy-6Y0LIA
 
>Yikes. When a fuse blows, you replace it *once*. If it blows again, it
>ain't the fuse or a line transient.
 
Yeah, well twice in this case. Replacing the RIFAs *usually* does the
trick (I have to say, in a half-arsed defence of my appalling
conduct).
 
 
>Start with a DMM and check for shorted diodes in the input bridge and
>then for a shorted filter cap at its output. (The schematic is more or
>less completely illegible, or I'd give the ref des.)
 
Not sure what you're viewing it with, Phil. Others don't seem to have
that problem and have been able to see the part numbers okay.
 
 
>Next most likely is a switch FET.
 
Yes, the chopper is always a prime suspect with SMPSs
 
Cursitor Doom <cd@notformail.com>: Oct 25 08:34AM +0100

On Mon, 24 Oct 2022 16:52:59 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
><https://www.promationusa.com/robotic-soldering-glance>
>and even more:
><https://www.google.com/search?q=hand+soldering+robot&tbm=isch>
 
Maybe one day I can get myself one of those, Jeff! :-D
legg <legg@nospam.magma.ca>: Oct 25 09:36AM -0400

On Mon, 24 Oct 2022 10:35:23 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
>The effect is more visible with a panel meter than with a digital
>readout (except when the meter is moving because I'm turning the crank
>on the Megger).
 
The video shows testing of two Y caps. These were originally
factory tested at 1500VAC/2700VDC, and have no reputation
for embarrassing field failures after 20+yrs.
 
X2 caps are desiged for 'impedance-limited' applications and
are tested at around 1KVAC/1500VDC.
>that failed have warped, cracked, melted, or crumbled outer plastic
>cases. For meaningful microscopy, I would need an old RIFA capacitor
>in an intact case.
 
Case degradation is a significant factor in aging of early production.
Prior to single-board assembly mfring philosophy, these parts were
shipped with long leads, loose, in bulk containers, knocking heads
all the way. They were then subjected to short and long term lead
stress in manual lead dressing and final physical attachment.
 
Rifa was first to use that distinctive clear lacquer. I'm not sure
how many times that formula was 'improved', but parts would arrive
with visible cracks and would crumble around lead wires during
lead-forming.
 
That being said, there were sufficient 'incidents' in the first
20yrs of use to ensure that nobody in their right minds would
use them in new product, even in a list of alternates, in the
last 25 years.
 
TEK scopes that employ these parts are antiques, maintained by
enthusiasts, who will tell you all about the effects of heat,
humidity and just plain age on plastics, epoxies and other
components/materials used in them.
 
RL
legg <legg@nospam.magma.ca>: Oct 25 09:53AM -0400

On Mon, 24 Oct 2022 17:21:00 -0700 (PDT), Phil Allison
> Strangely they are also the most expensive X2 caps on offer for no good reason.
> Described as being of "metalised , impregnated paper " construction.
> Rifa also claim to be the only supplier .
 
Phil,
 
You will not be able to purchase the 'exact' replacement, as the
series number no longer has the same operating voltage markings,
safety approval listing, pert numbering or material construction.
 
After all the merging and take-overs are done, it's unlikely
to be manufactured at the same physical plant, or using
similar equipment or materials, though safety docs used to be
pretty inflexible in that regard - one of the main trade effects
of VDE/IEC safety regime.
 
Costs reflect a low volume mfring environment due to buyer
reluctance to bother with 'improved' parts.
 
RL
Jeff Liebermann <jeffl@cruzio.com>: Oct 25 09:23AM -0700

On Mon, 24 Oct 2022 20:38:01 -0400, Phil Hobbs
 
>(The schematic is more or
>less completely illegible, or I'd give the ref des.)
 
https://disk.yandex.com/i/UhxATIy-6Y0LIA
The Yandex viewer is blurry, even when viewed as "original size".
 
Try downloading the PNG file and viewing it with a better viewer at
100% magnification. The details are quite readable in Irfanview
(Windoze) and Nomacs (Linux). In Irfanview, the image can be
"Sharpened" by hitting "S" on the keyboard.
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
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Digest for sci.electronics.repair@googlegroups.com - 16 updates in 3 topics

9:40 AM Penedão 0 comments
Ali J <ali.jaffar07@gmail.com>: Oct 24 01:39AM -0700

On Saturday, July 9, 2022 at 11:00:39 AM UTC-4, Peter W. wrote:
 
> True, "Caveat Emptor" is applicable. At the same time, the Solar Industry, and its Shills owes the average consumer honest and complete answers to specific questions. Certainly no less than that. What is clear, however, from the advertising out there is that those 'honest answers' are thin on the ground.
> Peter Wieck
> Melrose Park, PA
 
 
I just came across some good news here about solar's many benefits in Pennsylvania: https://inspiritingly.com/solar-pa/
 
Beyond reducing your utility bill, the tax credits are amazing, standing at 26% federal, in addition to much more from States and even some local financial incentives. Not only that but it provides American jobs that CAN'T be outsourced.
"Peter W." <peterwieck33@gmail.com>: Oct 24 04:11AM -0700

Latest proposal we had from a 'legitimate' solar installer (September) would cost us $32,000 up front, $22,400 after subsidies, and have an 11year, 4 month payback. Not my numbers. The installer offered, what he described as 'very generous' financing at 3.2%. That comes it at $218.37 per month for ten years, or a total of $26,204.40. Extending the payback to just over 13 years. Again, not my numbers, but those provided by the installer. This for a 10KW roof-mounted installation. Not including any related roof repairs. Yes, we have enough roof facing south to accommodate this level of installation.
 
At this moment, we have a locked in contract with a renewable provider for our electric power at $0.0630 KWH for the next three years, with four (4) three-year options at a capped rise of 8% every three years. Our present monthly electric bill (annual average/12) is $140/month. Let's use the rate after the third option $152.28. We will pay our local utility to transport the power in any case one way or the other, but somewhat less for the power we consume on-site - which will not be transported. So, let's look at a blended rate of $0.10/KWH, vs. the $0.14 we are paying now for both generation and transport. And let's use 20% of our present consumption. So, we will still be paying the power company $37/month for small use, and connection fees. So, our average savings will be, in reality, very roughly $120/month. Factor inflation, make that $200/month.
 
$26,204.40/200 = 131 months, several days. So, a better number is about an 11 year payback. Better than 'promised' by a few months. What we have not calculated:
 
a) Any roof repairs - minimal in our case as the roof is only three years old with a 30-year NDL warranty.
b) Increase in our homeowner's insurance - per our agent (Farmers), that would come to about $400/year.
c) Maintenance & repair (M&R) - life of a single grid-tie inverter is about 10 years, and the cost would be about $3,500 installed. Micro-Inverters (panel mounted) have about a 6-year life and require removal of the panel to repair. Not cheap. Does not include snow and leaf removal. Solar panels are series-mounted cells, so if one cell goes 'dark' the entire string goes dark.
d) Eventual removal, disposal, and roof repair at end-of-life.
 
Or, I can have power delivered from the Rocky Ridge wind farm in central PA at a reasonable cost. And have someone else worry about it.
 
And, take that same $218.37 and put it into an annuity at 4.2% - what they are paying these days - and have $37,208 in the bank after that same 11 years.
 
We are pretty efficient for a 4,200 s.f. three-story center-hall colonial built in 1890. We use splits (SEER 25) for heating and cooling, central heat is a 97% efficient boiler, and there are thermostatic valves on the radiators. So, we can keep the house at a reasonable 58 - 60F in the winter, and eight rooms have splits in them which we may set at any temperature we like.
 
And, at no time did we steal from other taxpayers.
 
Peter Wieck
Melrose Park, PA
"Peter W." <peterwieck33@gmail.com>: Oct 24 09:09AM -0700

Fascinating that you should link to a Canadian website registered just in June of 2022, and updated just today. And, per my protection software, also a phishing site.
"Peter W." <peterwieck33@gmail.com>: Oct 24 09:11AM -0700

Not to pile it on or anything:
 
https://ecogenamerica.com/cost-of-solar-panels-in-pa/
Cursitor Doom <cd@notformail.com>: Oct 23 05:58PM +0100

On Sun, 23 Oct 2022 09:36:24 -0700 (PDT), "Peter W."
 
>If the alternative is landfill, then heroic measures are justified.
 
I totally get where you're coming from here.
 
>If the alternative is 'sending it out', unless you wish to did deeper - and all indications are that you do not - then go ahead and send it out.
 
I'm not sure it's worth the expense, because there's another fault
with this scope that will most likely still be present even if the
present one is fixed. In fact, this 'other fault' may well have caused
the current one. This 'other fault' involved the displayed traces
suddenly turning extremely bright, accompanied by lines of dots. It
materialised only rarely, but I was out of the room when the scope
went *phut* so have no idea if there's any link to the current fault
or not.
I'm beginning to suspect those caps may have failed at some time in
the past, because for them to go *bang* with that amount of crap
sprayed everywhere must surely have resulted in a great deal of acrid
smoke being released - yet there was none discernable. And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short) then the scope can contintue to
function pretty well as normal so long as the mains supply is
reasonably clean.
 
>There is no magic bullet.
 
How true!
Jeff Liebermann <jeffl@cruzio.com>: Oct 23 11:16AM -0700

On Sat, 22 Oct 2022 15:26:04 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 
>Hi all,
 
Bah Humbug.
 
>So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
>main fuses (the 2A one on the rear panel).
 
"Oscilloscope Restoration Project - Repair Tektronix 2465B 400MHz"
<https://cdn.hackaday.io/files/1638907011869760/Tektronix-2465A-B-Oscilloscope-Restoration-Repair.pdf>
"Symptoms: This is my lab unit, which suddenly started blowing its
main AC fuse."
 
"Amazing Tektronix 2465 Repair Information"
<https://jestineyong.com/amazing-tektronix-2465-repair-information/>
Concerning my Tektronix 2465 repair I yesterday
replaced both 0.068uF 250VAC caps after I had
received the ordered new 275VAC caps.
 
Both caps are C1016 and C1018 in the Tektronix
service manual schematic on Board A2A1. And
only the C1016 0.068uF capacitor had blown
which also damaged the serie resistor R1016
of 68 ohm 5% which also was replaced.
 
They protect the Diode Bridge CR1011 (600V
3A Fast Recovery type RKBPC606-12) against
damage by high AC power voltages. The Diode
Bridge was not damaged. My oscilloscope is
happily working as new again. (48019 HRS of
service in 32 years or so).
 
Good luck.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
whit3rd <whit3rd@gmail.com>: Oct 23 02:13PM -0700

On Saturday, October 22, 2022 at 7:26:11 AM UTC-7, Cursitor Doom wrote:
> still blowing fuses. I can't be 100% certain, but I'm pretty sure
> there's a fault with the PSU board as I get the briefest whiff of
> burning from that area each time I put a new fuse in and power up.
 
First thing to check is the rectifier; that diode bridge can fail, and
apply AC to the filter capacitors, and... that'll take out the fuse.
Not sure why the RIFA capa goes, though; maybe just a power surge some
time last week?
 
There seem to be some surge-suppressors (gas discharge?) in the diagram, they might
have failed short in a surge..
Cursitor Doom <cd@notformail.com>: Oct 23 10:56PM +0100

On Sun, 23 Oct 2022 14:13:30 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:
 
>time last week?
 
>There seem to be some surge-suppressors (gas discharge?) in the diagram, they might
>have failed short in a surge..
 
Yes, they're each showing about 70k ohms, so can't be responsible.
 
One thing I forgot to mention in my first post was that a wire had
come adrift from the cooling fan's supply (poor factory soldering
clearly) so this unit had been running for an unknown length of time
with no fan. Not sure if that's relevant to the fault here, but it
certainly *could* be....
Cursitor Doom <cd@notformail.com>: Oct 23 10:57PM +0100

On Sun, 23 Oct 2022 11:16:19 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
 
>"Amazing Tektronix 2465 Repair Information"
><https://jestineyong.com/amazing-tektronix-2465-repair-information/>
 
>Good luck
 
Thanks for the links, Jeff; I'll check 'em out...
Phil Allison <pallison49@gmail.com>: Oct 23 04:41PM -0700

st...@swingnn.com wrote:
----------------------------------------------
Phil Allison
 
> I was pointing out a common misunderstanding with multiple capacitors.
> Rifa are alone, in parallel or in series and can all fail at the same
> time as can smoothing capacitors in parallel.
 
** Shame how you own example contradict that idea.

......Phil
Phil Allison <pallison49@gmail.com>: Oct 23 04:46PM -0700

Cursitor Doom wrote:
---------------------------------
> And if those
> caps fail open circuit (which they both did despite being X2 safety
> ones which are supposed to fail short)

** Really ? Where did you get that idea?
 
Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.
 
But those Rifa ones love to smoke and burn.
 
.......Phil
Jeff Liebermann <jeffl@cruzio.com>: Oct 23 05:13PM -0700

On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
>X2 dropping caps used in smoke alarms regularly fail open.
 
>But those Rifa ones love to smoke and burn.
 
>.......Phil
 
RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:
 
"Old RIFA capacitors and a disaster story"
<https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/>
 
YouTube videos featuring smoking RIFA caps:
<https://www.youtube.com/results?search_query=rifa+capacitor>
 
I sometimes test the HV leakage in capacitors using an ancient Megger:
<http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg>
<https://www.vintage-radio.net/forum/showthread.php?t=73265>
Unsolder the capacitor for testing. You really don't want a high
voltage power source connected to your oscilloscope.
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
legg <legg@nospam.magma.ca>: Oct 24 09:29AM -0400

On Sat, 22 Oct 2022 15:26:04 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 
>Thanks,
 
>CD.
 
>https://disk.yandex.com/i/UhxATIy-6Y0LIA
 
Don't know your line voltage, but if it's 240, check the
input voltage setting on the scope.
 
If RFI caps are replaced and bridge is ok, check big
electros (C1021, C1022) and main switch (Q1050) for
shorts.
 
At 240V, a leaky bulk cap can blow the gas tubes.
 
Once a gas tube fires, it's breakover voltage will
reduce, so must be replaced, too.
 
RL
legg <legg@nospam.magma.ca>: Oct 24 09:46AM -0400

On Sun, 23 Oct 2022 17:13:54 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
 
><https://www.vintage-radio.net/forum/showthread.php?t=73265>
>Unsolder the capacitor for testing. You really don't want a high
>voltage power source connected to your oscilloscope.
 
The smoking caps were metalized paper construction. These were good
enough in their day, with a demonstrated mtbf and safe self-healing,
while seals lasted. The outer sealing body tended to shrink and crack
with age, allowing ingress of air and moisture, compromising
performance. They are no longer made.
 
Metalized film parts are usually less dramatic in self-clearing
of internal faults, but in extreme cases, you still get thermal
runaway, as the faulting area expands and eats away at succesive
layers of the wrapped structure.
 
Film parts will generally fail at the end schoopage joint, where
metalization and film stresses accumulate in mfring.
 
RL
ehsjr <ehsjr@verizon.net>: Oct 23 01:20PM -0400

On 10/22/2022 11:57 PM, John Crane wrote:
 
> It's a 12-181b.
 
> As luck would have it, it came with a little paper schematic and user's
> guide tucked in the battery compartment....attaching a jpg of it.
 
Below is a relatively long post concerning a lower probability
cause of the problem than the cube itself. It was mentioned
earlier, but dismissed when it should not have been. I'm
posting this because there is a small possibility that there
is a safety issue in your home.
 
You have NOT eliminated all possibilities of EMI/RFI
Walk it down the road, as was mentioned. That is, take
it somewhere to a place far away from any power lines,
houses, buildings etc where electrical devices are.
If it still buzzes then you know the problem is within
the cube. Sources of EMI/RFI can be in a nearby neighbor's
house, a power line fault such as a cracked insulator
or even a loose connection in the wiring in your house.
It doesn't have to be a new electrical device in your
house, even though that is a most likely cause in many
cases.
 
If the cube works properly when walked down the road,
but starts buzzing as you near your house, use it as
a detector to try to locate the source - perhaps a
power line or a neighbor's house. If the source is
something in your house, you can shut off breakers
until you determine which circuit "hosts" the noise
making device, then further isolate by restoring power
to the circuit and unplugging/switching off one device
at a time. Don't overlook devices that you cannot
switch off like doorbell or thermostat transformers
hard wired devices and so forth. If the problem is
not found in any device you can unplug or switch off,
it could be a loose connection in the wiring. That
is serious, as a fire could result.
 
I hope diagnosis/fix turns out to be simple and
does not involve safety at all. Good hunting!
Ed
Jeff Liebermann <jeffl@cruzio.com>: Oct 23 10:45AM -0700

On Sat, 22 Oct 2022 22:57:45 -0500, John Crane
 
>It's a 12-181b.
 
>As luck would have it, it came with a little paper schematic and user's
>guide tucked in the battery compartment....attaching a jpg of it.
 
Thanks. The schematic is somewhat out of focus but I was able to make
it more readable using the "Sharpen" feature in Irfanview.
 
I know both IC's quite well, having used them in various marine radio
designs around 1975. The MC3357 has a large amount of gain and is
therefore likes to oscillate with minimal provocation.
 
In order from most probable:
Electrolytics: C28, C15.
0.01uF ceramics: C22, C30, C10.
My best guess(tm) is C15.
 
Also, check the DC voltage across D4. It should be 5.1VDC
 
I suggest you bypass the capacitors with a replacement capacitor, one
at a time, instead of removing and replacing. It's quicker and
easier. If you need to remove the wax, a hair dryer or heat gun will
work.
 
MC3357 datasheet:
<https://www.digchip.com/datasheets/download_datasheet.php?id=643405&part-number=MC3357>
 
I can think of some less likely failures and parts if cap replacements
show no improvement. As I previously suggested, probe the PCB with
your finger and look for an area that produces a change in the buzzing
noise. Whatever failed is nearby.
 
 
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
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Digest for sci.electronics.repair@googlegroups.com - 6 updates in 2 topics

9:40 AM Penedão 0 comments
Cursitor Doom <cd@notformail.com>: Oct 22 03:26PM +0100

Hi all,
 
So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel). I opened the case and found
two RIFA caps that had obviously blown, so replaced them, but it's
still blowing fuses. I can't be 100% certain, but I'm pretty sure
there's a fault with the PSU board as I get the briefest whiff of
burning from that area each time I put a new fuse in and power up. The
new fuse blows again before I get to see any smoke coming from
anywhere at all. I'm linking to a diagram of the PSU as I'm not
familiar with this circuit topology. If anyone can spot a component
here that could have gone low-resistance and might be a good candidate
for out-of-circuit testing, by all means let me know.
Thanks,
 
CD.
 
 
https://disk.yandex.com/i/UhxATIy-6Y0LIA
"Peter W." <peterwieck33@gmail.com>: Oct 22 08:08AM -0700

Did the caps fail Open or Short?
 
Peter Wieck
Melrose Park, PA
"ohg...@gmail.com" <ohger1s@gmail.com>: Oct 22 08:57AM -0700

On Saturday, October 22, 2022 at 10:26:11 AM UTC-4, Cursitor Doom wrote:
> Thanks,
 
> CD.
 
> https://disk.yandex.com/i/UhxATIy-6Y0LIA
 
 
Did you do any resistance checks like for a shorted rectifier(s) or power transistor like Q1050? FWIW, installing a new fuse and waiting for smoke is a terrible idea.
John Crane <john_crane_59@yahoo.com>: Oct 21 07:41PM -0500

Bought one in excellent shape.
Worked great for about a month, then developed a buzzing background
noise in the audio - but you can still hear the weather reports. Just
annoying.
 
It's been sitting on a shelf the whole time. And 9V battery powered.
 
I tried replacing all the electrolytic caps, but no go. In fact, the
buzz is slightly louder.
 
Any ideas as to what could cause this?
Jeff Liebermann <jeffl@cruzio.com>: Oct 21 08:34PM -0700

On Fri, 21 Oct 2022 19:41:26 -0500, John Crane
 
>I tried replacing all the electrolytic caps, but no go. In fact, the
>buzz is slightly louder.
 
>Any ideas as to what could cause this?
 
Does the buzzing follow the volume control? In other words, does
turning the volume up and down change both the weather report AND the
buzzing, or is the buzzing a constant level?
 
The problem might a new source of EMI (electromagnetic interference).
Try moving the cube around the house and see if the buzzing gets
stronger near some new electronic or motorized equipment. Also try
moving the cub outside and down the road to see if it goes away with
distance.
 
I once had a weather cube. I found that nearly dead 9V batteries
would cause the audio state to "motorboat". It was easier to replace
the battery than the fix the problem, so I never troubleshot it down
to the failed component. I suspect you might have a similar problem
if you're using a rechargeable LiIon 9V battery, some of which only
produce 7.2VDC. If you have a new 9V alkaline battery, try it.
 
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558
John Crane <john_crane_59@yahoo.com>: Oct 21 11:01PM -0500

On 10/21/22 10:34 PM, Jeff Liebermann wrote:
> to the failed component. I suspect you might have a similar problem
> if you're using a rechargeable LiIon 9V battery, some of which only
> produce 7.2VDC. If you have a new 9V alkaline battery, try it.
 
The buzzing follows the volume control, it's not constant.
 
Moving it around the house doesn't affect the buzzing. It stays at a
constant level. And no new equipment came online in the house since it's
been in use.
 
My battery was a Duracell alkaline at 8.59V. I replaced it with another
Duracell at 9.19V. No change in the buzzing.
 
Really a strange problem. I'd suspect a bad connection somewhere, but
the problem just appeared slowly as it was used on a shelf. There was
no movement, or jarring involved that could have knocked something
loose. And there is a lot of wax poured over the components -
presumably to keep the little coils fixed in shape. I thought the
electrolytics finally gave out, as it's a vintage one with faux wood
grained sides. Maybe 70's - 80's era.
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