sci.electronics.repair - 25 new messages in 12 topics - digest

sci.electronics.repair
http://groups.google.com/group/sci.electronics.repair?hl=en

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Today's topics:

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TOPIC: EARN 10000 DOLLARS PER DAY - FOREX TRADING ONLINE TODAY
http://groups.google.com/group/sci.electronics.repair/t/73c3e41ab37dd53a?hl=en
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== 1 of 1 ==
Date: Tues, Feb 22 2011 10:37 pm
From: success all

http://USAforextradingonline.blogspot.com

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TOPIC: HOT SEXY GIRLS ADULT MOVIE AND BED ROOM SCENES HERE
http://groups.google.com/group/sci.electronics.repair/t/8f1749b9db02a762?hl=en
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== 1 of 1 ==
Date: Wed, Feb 23 2011 1:56 am
From: devi vithya

http://www.love4indianpeople.blogspot.com/

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TOPIC: Fender Blues deluxe, PR246
http://groups.google.com/group/sci.electronics.repair/t/06865a0707061c2e?hl=en
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== 1 of 4 ==
Date: Wed, Feb 23 2011 2:54 am
From: Ron

On 22/02/2011 22:13, Phil Allison wrote:
> "N_Cook"<
>>
>> Instead of the original 3x 12AX7 it now has 2 and 2x 12AT7 and a 5AR4
>> rectifier
>>
>
> ** You need to find a schem of the Bandmaster-Reverb Amp AA768.
>
> Shame all the ones Google turns up are illegible.
>
>
> .... Phil
>
>
I have the diags for AA768, it's not brilliant but fairly readable.
email me if you want a copy.

Ron

== 2 of 4 ==
Date: Wed, Feb 23 2011 3:41 am
From: "N_Cook"

Ron <ron@lunevalleyaudio.com> wrote in message
news:4ZidnStiRc3yevnQnZ2dnUVZ8s-dnZ2d@bt.com...
> On 22/02/2011 22:13, Phil Allison wrote:
> > "N_Cook"<
> >>
> >> Instead of the original 3x 12AX7 it now has 2 and 2x 12AT7 and a 5AR4
> >> rectifier
> >>
> >
> > ** You need to find a schem of the Bandmaster-Reverb Amp AA768.
> >
> > Shame all the ones Google turns up are illegible.
> >
> >
> > .... Phil
> >
> >
> I have the diags for AA768, it's not brilliant but fairly readable.
> email me if you want a copy.
>
> Ron

Ta for that, I have it in the Aspen Pittman Tube Amp vol 3 book which hapens
to be a very clear schematic.
I think I've found the distortion problem, duff 12AX7 socket pin. Remaining
problems are both large Tx only held to the chassis by wishful thinking. And
excess hum (for this owner), bad replacement pots (tagged, not the original
pcb ones). The output matcher had to be moved to accommodate a different
speaker, and not well mounted . Badly blanked off front panel holes for niow
deleted functions.
Other than the cab little seems original, o/p Tx, choke, knobs, chassis ,
valve bases and the jewel pilot lamp holder is about the sum of it
Luckily surplus Rexine in the amp cavity to salvage for where their pet
rabbit has eaten the exposed covering.
Researching the output bottles , nice little page about the company, I like
the "retro" industrial instrumentation
http://www.tubedepot.com/sed1.html
in operation since 1912 they presumably never lost the skill base

== 3 of 4 ==
Date: Wed, Feb 23 2011 8:19 am
From: "N_Cook"

Or like the AB868 with the vibrato ch removed

Another thing that has remained from the original. That manurey/goaty /
caproic acid smell that emerges when Fender (and other USA-made) amps are
opened to the air in the UK. No one else has come up with another
explanation - so I will stay with the US-patented use of fatty acids from
abattoir sources as a part of the formulation of the insulation of
transformer magnet wire. Then some reaction to UK humidity or UK-specific
microbial action. Not an unpleasant smell , just agricultural, not what you
expect to come from electronic kit.
This amp has a UK made mains transformer replacement so the smell , if from
inside the transformers then from the choke or the output Tx . I
deliberately kept the cab in another room this time , no smell there, so not
horse glue used in the cab making.

== 4 of 4 ==
Date: Wed, Feb 23 2011 6:18 am
From: "N_Cook"

Or like the AB868 with the vibrato ch removed

==============================================================================
TOPIC: Repairing NiCd battery packs
http://groups.google.com/group/sci.electronics.repair/t/0dcecdb70389a722?hl=en
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== 1 of 3 ==
Date: Wed, Feb 23 2011 2:58 am
From: mike

Smitty Two wrote:
> In article <MPG.27c9b0c2136cb40e98977d@news.eternal-september.org>,
> Andrew Rossmann <andysnewsreply@no_junk.comcast.net> wrote:
>
>> How easy/hard would it be to solder to them, and will
>> it damage the batteries if I try?
>
> If you scratch the areas to be soldered with sandpaper and *use liquid
> flux* then you can readily solder the batteries without damaging them.

If cells with solder tabs and the bulge caused by the solder and wire
still fit in the space, that's the way to go.
Be aware that QUALITY cells will cost more than the cost of a battery pack.

Dustbusters are sold on PRICE. That means low quality batteries
and chargers with zero control that overcharge/degrade the cells.
If you don't do something about the charger, your new cells won't
last any longer than the old ones did.

People tell you that you can safely solder on cells. That ain't the case.
Yes, if you're very experienced at soldering on batteries, you may
be able to do it most of the time without serious degradation.
If this is your first attempt, expect to ruin at least some of them.
If you must solder on 'em, do it with them discharged, so when you
melt the separator and create an internal short, there's less energy
to fuel the explosion. Wear eye protection, and make sure the kids are
outa the house. They're not lithium, so making sure your fire insurance
is paid up is a secondary issue.

I can hear the villagers lighting the torches to come after me to tell
me how stupid I am...that you CAN solder on batteries.
I even did it for a number of years. I am fortunate that I got old
enough to require glasses before the first one exploded in my face.
Otherwise, you'd be reading this in braille.

There's a reason they weld the tabs. Ignore that at your peril.
People who have to ask "how hard it is" should NOT be soldering on
batteries...even if some "newsgroup expert" says THEY can.

== 2 of 3 ==
Date: Wed, Feb 23 2011 3:27 am
From: "Phil Allison"

"mike"
>
> If cells with solder tabs and the bulge caused by the solder and wire
> still fit in the space, that's the way to go.

** There is a simple way to join ( un-tagged) cells very neatly, tip to
base, that uses just a few centimetres of 1.5 mm dia solid copper wire. Here
it is:

The copper wire ends are first tinned and one end soldered to the *side of
the tip* of one cell and then the other end soldered the outer edge of the
base of another. A quick twist and the two are perfectly connected in
series with no increase in overall length.

> People tell you that you can safely solder on cells. That ain't the case.
> Yes, if you're very experienced at soldering on batteries, you may
> be able to do it most of the time without serious degradation.
> If this is your first attempt, expect to ruin at least some of them.

** This is just not true.

> There's a reason they weld the tabs.

** It's quick, cheap and nasty.

Most spot welded joints have so much resistance the joint gets VERY HOT
when packs are subjected to a fast discharge - ie when used on RC models
involved in racing etc.

> People who have to ask "how hard it is" should NOT be soldering on
> batteries...even if some "newsgroup expert" says THEY can.

** You need a good soldering iron - preferably a modern, variable temp
station and iron rated at 50 watts with a large tip size fitted and full
setting ( ie 450C) on the temp dial.

Then one works quickly and purposefully with ordinary, rosin cored 60/40
solder. The nickel plated surfaces of fresh Ni-Cd or NiMH cells usually tin
so quickly - it fair makes your head spin.

..... Phil

== 3 of 3 ==
Date: Wed, Feb 23 2011 10:33 am
From: "WW"

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:8sb5qaFf01U1@mid.individual.net...
>
> "Andrew Rossmann"
>
>> Has anyone had any luck in replacing individual cells?
>
> ** Best to replace the lot.
>
>> There are no
>> markings on the batteries, so I have no idea what their capacity is.
>
> ** See above.
>
>
>> These are chained together with short metal strips that are spot-welded
>> to the batteries. How easy/hard would it be to solder to them, and will
>> it damage the batteries if I try?
>
> ** Try to get cells that have tags fitted to them.
>
> These are very easy to solder with any decent soldering iron and flux
> cored solder ( not lead free) as used for electronic work.
>
>
I do it that way. Flux and quick tin tab and cell. I use a 250 watt Wen gun
type. With high wattage the quicker it will solder with less heat expanse on
the cell. WW
> .... Phil
>
>
>
>

==============================================================================
TOPIC: Proxy to open blocked sites
http://groups.google.com/group/sci.electronics.repair/t/a790210194504e40?hl=en
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== 1 of 1 ==
Date: Wed, Feb 23 2011 1:57 am
From: Ahmed Ragab

Proxy to open blocked sites

http://ppropx.4mtm.net

http://pronet.4mtm.net

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TOPIC: 2 Digit LED counter design help needed
http://groups.google.com/group/sci.electronics.repair/t/4802b4acf12f92f4?hl=en
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== 1 of 3 ==
Date: Wed, Feb 23 2011 4:26 am
From: "Herman"

Almost all that you want
http://cgi.ebay.com/2-Digit-LED-Number-Display-UP-DN-Counter-4-Digits-/170606032472?pt=LH_DefaultDomain_203&hash=item27b8e97658

"Harlan" <hpgarbe@charter.net> wrote in message
news:590b8b5a-0c76-4d16-a02b-2796c03f9572@j9g2000prj.googlegroups.com...
>A customer is asking for a product that I am
> having trouble finding. I also might rather build it if I knew what
> was needed.
> Best way to explain is this: We've all been at a service desk where
> we've had to
> "take a number" to mark our place in line. Then they may also have a
> good sized
> digital display for the public to see which number is being served so
> you know
> your position "in queue".
>
> Well a customer (business) would like something like this where the
> employee can
> increase or decrease the displayed value (max of two digits) with the
> push of an
> up or down button . A clear or reset button would also be helpful.
>
> Another feature desired would be to "light up" another indicator,
> maybe the decimal
> point, on the display to indicate another condition that may become
> involved.
> Also it would be desirable to have a smaller LED display at the
> operator's desk
> to see and confirm the value being sent to the larger display which
> may not
> be easily seen from their location.
>
> I'm hoping someone here may have the knowledge to help me with a
> diagram
> and parts needed (maybe a source as well for the LED displays) With a
> schematic and any comments regarding the design, I think I could
> construct
> the project.
>
> Many thanks in advance !
>

== 2 of 3 ==
Date: Wed, Feb 23 2011 10:22 am
From: Harlan

On Feb 23, 6:26 am, "Herman" <r...@bellsouth.net> wrote:
> Almost all that you wanthttp://cgi.ebay.com/2-Digit-LED-Number-Display-UP-DN-Counter-4-Digits...
>
> "Harlan" <hpga...@charter.net> wrote in message
>
> news:590b8b5a-0c76-4d16-a02b-2796c03f9572@j9g2000prj.googlegroups.com...
>
>
>
> >A customer is asking for a product that I am
> > having trouble finding. I also might rather build it if I knew what
> > was needed.
> > Best way to explain is this: We've all been at a service desk where
> > we've had to
> > "take a number" to mark our place in line. Then they may also have a
> > good sized
> > digital display for the public to see which number is being served so
> > you know
> > your position "in queue".
>
> > Well a customer (business) would like something like this where the
> > employee can
> > increase or decrease the displayed value (max of two digits) with the
> > push of an
> > up or down button . A clear or reset button would also be helpful.
>
> > Another feature desired would be to "light up" another indicator,
> > maybe the decimal
> > point, on the display to indicate another condition that may become
> > involved.
> > Also it would be desirable to have a smaller LED display at the
> > operator's desk
> > to see and confirm the value being sent to the larger display which
> > may not
> > be easily seen from their location.
>
> > I'm hoping someone here may have the knowledge to help me with a
> > diagram
> > and parts needed (maybe a source as well for the LED displays) With a
> > schematic and any comments regarding the design, I think I could
> > construct
> > the project.
>
> > Many thanks in advance !- Hide quoted text -
>
> - Show quoted text -

Thanks for all the input. I had Googled a lot for "2 digit LED counter
display" trying to be more direct but only came up with
vaguely related forums, partial items... ie... no real help. Since
"take a number" didn't seem quite what I was looking for,
I never really Googled it till now. And.... came up with 2-3
manufacturers that make just about exactly what I'm looking for.
The price may be quite a bit more than hoped but then it is a lot of
hassle to build the circuitry, the enclosures, etc and
have it look "professional". So... again thanks and now we have some
options.
Best regards to all.

== 3 of 3 ==
Date: Wed, Feb 23 2011 4:02 pm
From: "Dave M"

Harlan wrote:
> On Feb 23, 6:26 am, "Herman" <r...@bellsouth.net> wrote:
>> Almost all that you
>> wanthttp://cgi.ebay.com/2-Digit-LED-Number-Display-UP-DN-Counter-4-Digits...
>>
>> "Harlan" <hpga...@charter.net> wrote in message
>>
>> news:590b8b5a-0c76-4d16-a02b-2796c03f9572@j9g2000prj.googlegroups.com...
>>
>>
>>
>>> A customer is asking for a product that I am
>>> having trouble finding. I also might rather build it if I knew what
>>> was needed.
>>> Best way to explain is this: We've all been at a service desk where
>>> we've had to
>>> "take a number" to mark our place in line. Then they may also have a
>>> good sized
>>> digital display for the public to see which number is being served
>>> so you know
>>> your position "in queue".
>>
>>> Well a customer (business) would like something like this where the
>>> employee can
>>> increase or decrease the displayed value (max of two digits) with
>>> the push of an
>>> up or down button . A clear or reset button would also be helpful.
>>
>>> Another feature desired would be to "light up" another indicator,
>>> maybe the decimal
>>> point, on the display to indicate another condition that may become
>>> involved.
>>> Also it would be desirable to have a smaller LED display at the
>>> operator's desk
>>> to see and confirm the value being sent to the larger display which
>>> may not
>>> be easily seen from their location.
>>
>>> I'm hoping someone here may have the knowledge to help me with a
>>> diagram
>>> and parts needed (maybe a source as well for the LED displays) With
>>> a schematic and any comments regarding the design, I think I could
>>> construct
>>> the project.
>>
>>> Many thanks in advance !- Hide quoted text -
>>
>> - Show quoted text -
>
> Thanks for all the input. I had Googled a lot for "2 digit LED counter
> display" trying to be more direct but only came up with
> vaguely related forums, partial items... ie... no real help. Since
> "take a number" didn't seem quite what I was looking for,
> I never really Googled it till now. And.... came up with 2-3
> manufacturers that make just about exactly what I'm looking for.
> The price may be quite a bit more than hoped but then it is a lot of
> hassle to build the circuitry, the enclosures, etc and
> have it look "professional". So... again thanks and now we have some
> options.
> Best regards to all.

Don't go away yet!!!
As we speak, there's a DEAL!! for exactly what you're looking for from
Electronic Goldmine. I'll bet you can't find a better price, either. Look
at
http://www.goldmine-elec-products.com/prodinfo.asp?number=G16774&utm_source=Electronic+Goldmine+Newsletter&utm_campaign=1698280656-Feb23&utm_medium=email
and see if it's to your liking. Heck, for the price, get one to use and a
couple more for spares.

Cheers,
--
David
dgminala at mediacombb dot net

==============================================================================
TOPIC: Pioneer PD-M610 6cd player service manual
http://groups.google.com/group/sci.electronics.repair/t/fa0608d06708250e?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Feb 23 2011 5:10 am
From: F Murtz

Pioneer PD-M600 changer. Presents disc but does not spin up then the
same thing happens with each disc.
Anyone any clues or where to get service manual, preferably free.

== 2 of 3 ==
Date: Wed, Feb 23 2011 2:25 pm
From: sam@repairfaq.org (Samuel M. Goldwasser)

F Murtz <haggisz@hotmail.com> writes:

> Pioneer PD-M600 changer. Presents disc but does not spin up then the
> same thing happens with each disc.
> Anyone any clues or where to get service manual, preferably free.

Bad flex cable, dropped lens, dirty spindle motor, decayed rubber grommets,
etc.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

== 3 of 3 ==
Date: Wed, Feb 23 2011 4:51 pm
From: F Murtz

Samuel M. Goldwasser wrote:
> F Murtz<haggisz@hotmail.com> writes:
>
>> Pioneer PD-M600 changer. Presents disc but does not spin up then the
>> same thing happens with each disc.
>> Anyone any clues or where to get service manual, preferably free.
>
> Bad flex cable, dropped lens, dirty spindle motor, decayed rubber grommets,
> etc.
>
Motor does not attempt to start spinning,Have not checked for voltage at
spindle motor yet, just had quick look so far.
Would feel happier with schematic but the only ones I can find want
money and I am a bit wary of paying for a pig in a poke.

==============================================================================
TOPIC: HOT SEXY GIRLS ENJOYING BED ROOM SCENES AND XXXX VIDEOS HERE
http://groups.google.com/group/sci.electronics.repair/t/44e30918422a5198?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Feb 23 2011 5:35 am
From: cinema

http://www.love4indianpeople.blogspot.com/

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TOPIC: Looking For Usable Multimeter - Cheap
http://groups.google.com/group/sci.electronics.repair/t/e1a0542b17d8b08d?hl=en
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== 1 of 1 ==
Date: Wed, Feb 23 2011 8:21 am
From: Peabody

JeffM says...

> There's a bi-monthly swap meet near me for computer
> stuff, etc. that has old voltmeters (analog too!). They
> are mostly returns that somebody blew the fuse in and
> returned. Watching a needle move *can* give useful
> information that a digital readout doesn't easily
> communicate.

I agree. I use mine all the time, but the contacts inside
are wearing out. Where would you find an inexpensive new
analog meter? Do they even make them anymore?

==============================================================================
TOPIC: Supercaps and ESR
http://groups.google.com/group/sci.electronics.repair/t/2ca41182f5f15ef4?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Feb 23 2011 5:38 am
From: andrew@cucumber.demon.co.uk (Andrew Gabriel)

In article <0001HW.C9895AE3005BC238B042E9BF@news.eternal-september.org>,
DaveC <invalid@invalid.net> writes:
> Trying to find a replacement for a 1F/2.5V supercap.
>
> Original:
>
> <http://www.newark.com/cooper-bussmann/b0810-2r5105-r/capacitor-super-1f-2-5v-
> 0-4ohm/dp/78K7800?Ntt=B0810-2R5105-R>
>
> I can find local replacements rated 1F/5V but the ESR is ~30 ohms instead of
> 0.4.
>
> I presume that supercaps aren't applied to filter applications -- their
> specialty being an alternative to batteries to power memory or such -- so
> ripple current shouldn't be an issue.
>
> My question: what's the impact of replacing a supercap with one with a higher
> ESR?

Depends on the application.
Some are designed to provide backup power at low currents for long periods.
Some are designed to provide high power at high currents for short periods.
The latter type won't like an increase in ESR.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

== 2 of 3 ==
Date: Wed, Feb 23 2011 11:03 am
From: "John Gilmer"

"Jeffrey Angus" <jangus@suddenlink.net> wrote in message
news:4d6423bb$0$4302$bbae4d71@news.suddenlink.net...
> On 2/22/2011 2:52 PM, Meat Plow wrote:
>> On Tue, 22 Feb 2011 12:21:55 -0800, DaveC wrote:
>>
>>> My question: what's the impact of replacing a supercap with one with a
>>> higher ESR?
>>
>> Logic would dictate it would discharge quicker but my logic is usually
>> flawed.

Huh!

The higher the ESR the lower the peak current you can draw from it and the
longer it will take to fully charge with a given source.
>
> Considering that the draw on these caps is usually measured in
> microamps, I doubt the higher ESR is going to effect how well
> it works.

Huh? (Again!)

The draws are usually measured in the 10s of Amperes. In some
applications, the 100s of Amperes (such as when a super cap is used to help
start something.)

>
> Maybe might make a bit of difference in how long it takes to
> fully charge though.

That but also how much the cap heats when both charging the discharging.
If it's being used in a power supply filtering function, a high ESR will
both reduce the filtering effect and increase the heating of the cap.

== 3 of 3 ==
Date: Wed, Feb 23 2011 11:16 am
From: Tim Shoppa

On Feb 22, 3:21 pm, DaveC <inva...@invalid.net> wrote:
> Trying to find a replacement for a 1F/2.5V supercap.
>
> Original:
>
> <http://www.newark.com/cooper-bussmann/b0810-2r5105-r/capacitor-super-...
> 0-4ohm/dp/78K7800?Ntt=B0810-2R5105-R>
>
> I can find local replacements rated 1F/5V but the ESR is ~30 ohms instead of
> 0.4.
>
> I presume that supercaps aren't applied to filter applications -- their
> specialty being an alternative to batteries to power memory or such -- so
> ripple current shouldn't be an issue.
>
> My question: what's the impact of replacing a supercap with one with a higher
> ESR?

I think it depends on application. I haven't done detailed measurement
but I would postulate that the low-ESR supercaps have more surface
area and higher leakage, and the higher-ESR supercaps have less
surface area and less leakage.

Tim.

==============================================================================
TOPIC: Unidentified connector type
http://groups.google.com/group/sci.electronics.repair/t/1b97e6c49da959fe?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Feb 23 2011 2:27 pm
From: sam@repairfaq.org (Samuel M. Goldwasser)

Please see:

http://repairfaq.cis.upenn.edu/Misc/conn-h.jpg
http://repairfaq.cis.upenn.edu/Misc/conn-p.jpg

These are 0.1" spaced and sort of compatible with the common AMP/Molex
headers/housings but not quite identical. Please don't do an extensive
search, but if you recognize the manufacturer/type, please reply here.

Thanks!

==============================================================================
TOPIC: Electrolytics blow after 1 hr
http://groups.google.com/group/sci.electronics.repair/t/22739e68af51f6a4?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Feb 23 2011 4:42 pm
From: Jeff Liebermann

Another day in bad caps hell. I fish a Dell GX520 out of the pile at
the local recycler and proceed to try and raise the dead. I've done
this many times with good success, but not this time. Upon initial
inspection, I find the usual bulging electrolytic caps. There were 4
identical caps, 2200uF 6.3VDC 105C. I replace them with 2200uF 10VDC
105C caps (Panasonic ECA-1AHG222). Note the increase in working
voltage. These are brand new caps from Digikey. I run the unit
overnight and find that two of the caps now have bulging tops.

Assuming that I may have had some marginal caps in the bag (unlikely
but worth testing), I replace the two that bulged with 2200uF 10v 85C
caps (Panasonic ECA-1AM222) also from Digikey. This is somewhat of a
downgrade, but should work. I also replace the power supply, for no
better reason than I had a spare.

Same problem as before. The two caps blew their tops within a few
hours, leaking caustic goo.
<http://802.11junk.com/jeffl/crud/GX520-bad-caps.jpg>
The two large black caps in the foreground are the surviving 105C
caps, while the blue caps in the background, are the bulging 85C caps.

Using my finger and a thermocouple thermometer, I determined that the
bulging caps are not getting warm or at least are not any warmer than
other nearby components.

I've replace literally hundreds of caps but I've never seen this
before. It really makes me wonder if the bad caps problem might be
caused by something other than defective caps and/or marginal
capacitor voltage ratings.

Duz anyone have a clue as to what is causing this problem? I haven't
had time to probe the board for power supply bus noise or excessive
current quite yet. What I could use is some speculation as to the
probable culprit.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

== 2 of 3 ==
Date: Wed, Feb 23 2011 4:58 pm
From: "William Sommerwerck"

Bad rectifier letting AC through to the caps?

== 3 of 3 ==
Date: Wed, Feb 23 2011 5:38 pm
From: Jamie

Jeff Liebermann wrote:
> Another day in bad caps hell. I fish a Dell GX520 out of the pile at
> the local recycler and proceed to try and raise the dead. I've done
> this many times with good success, but not this time. Upon initial
> inspection, I find the usual bulging electrolytic caps. There were 4
> identical caps, 2200uF 6.3VDC 105C. I replace them with 2200uF 10VDC
> 105C caps (Panasonic ECA-1AHG222). Note the increase in working
> voltage. These are brand new caps from Digikey. I run the unit
> overnight and find that two of the caps now have bulging tops.
>
> Assuming that I may have had some marginal caps in the bag (unlikely
> but worth testing), I replace the two that bulged with 2200uF 10v 85C
> caps (Panasonic ECA-1AM222) also from Digikey. This is somewhat of a
> downgrade, but should work. I also replace the power supply, for no
> better reason than I had a spare.
>
> Same problem as before. The two caps blew their tops within a few
> hours, leaking caustic goo.
> <http://802.11junk.com/jeffl/crud/GX520-bad-caps.jpg>
> The two large black caps in the foreground are the surviving 105C
> caps, while the blue caps in the background, are the bulging 85C caps.
>
> Using my finger and a thermocouple thermometer, I determined that the
> bulging caps are not getting warm or at least are not any warmer than
> other nearby components.
>
> I've replace literally hundreds of caps but I've never seen this
> before. It really makes me wonder if the bad caps problem might be
> caused by something other than defective caps and/or marginal
> capacitor voltage ratings.
>
> Duz anyone have a clue as to what is causing this problem? I haven't
> had time to probe the board for power supply bus noise or excessive
> current quite yet. What I could use is some speculation as to the
> probable culprit.
>
Try using Low ESR caps in that circuit... Most switching signals need
caps with virtually no R in them.. Otherwise, they'll heat up in side
a bit and vent, or partially get there.

Jamie

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