sci.electronics.repair - 25 new messages in 11 topics - digest

sci.electronics.repair
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Today's topics:

==============================================================================
TOPIC: electric fence , force field B20, 2007
http://groups.google.com/group/sci.electronics.repair/t/9573289f9ec521ea?hl=en
==============================================================================

== 1 of 5 ==
Date: Tues, Jun 29 2010 12:40 am
From: "N_Cook"

8 pin SMD with blown hole in the casing. Top mark , very indistinct maybe 2
lines
0h963
0h37

maybe very stylised 4 instead of h, logo very indistinct. My first guess is
a 555 but pinning not standard
p3 ground, p8 +12V, pin 1 to a 10uF cap , other end to 0V, p5 tied to p6
goes to speed change pot with also a line from the pot to p1. No obvious
output trace.
Removed the device and internal connections between p2 and 3 presumably
fried , and also p6 and 7
Other device is a 16 pin with ident scraped off or the conformal coating
dissolved off.

In passing , a 8x5x3 mm fuse with bo encapsulation , mainly 2 bare Al plates
with something between. Working order measures 0.18R +/-.01R, marked/punched
in the Al
100
B7L
never seen anything like it before
make/series/value?

== 2 of 5 ==
Date: Tues, Jun 29 2010 2:06 am
From: "N_Cook"

== 3 of 5 ==
Date: Tues, Jun 29 2010 3:49 am
From: "N_Cook"

The fuse is surface mount , I suppose as high current draw, if only
intermittant ,it has to be quite high current, perhaps 10 amp from the 100
marking. Top face 8x5mm bent down the 3 mm over the other plate to one pad
and the other smaller plate , about 6x45mm to the other pad and some thin
material in between
of this form, polyswitch
http://www.westfloridacomponents.com/IC523PE05/40A+15V+1.9W+Resettable+SMT+P
olyswitch+Fuse+Tyco+SMD250-2.html
perhaps 10 amp version

== 4 of 5 ==
Date: Tues, Jun 29 2010 4:46 am
From: "N_Cook"

The main 14 pin SMD has no trace to 12V but p1 goes to this 8 pin SMD which
is connected to 12V so presumably some sort of current or voltage control
requiring 0 and 12V and the pot connection changes the current/V, not the
speed from "Normal" setting to "Turbo" at the top of pot range, and the
output somehow chopped or something from the 12V , smoothed by the 10uF.

== 5 of 5 ==
Date: Tues, Jun 29 2010 7:21 am
From: "N_Cook"

Those polyswitch resetable fuses may have problems in hot conditions.
Breathing on this one for 5 sec raises the 0.18R to double or so and a
soldering iron barrel switched off and cooled for 2 minutes, laid on it, is
enough to raise to kohm. Alternatively useful highly non linear thermal
sensing elements.

So far have not found a buck boost L-free version of DC to DC converter ,
step down, IC, presumably made variable via use of the pot rather than a
zener. L free version of Maxim MAX758,830,724 or 726 if anyone knows of
something that fits the bill?
This fence is stated to run on 9V as well as 12V battery so I suppose i/p 5
to 15V and output perhaps 6 to 13V or so

==============================================================================
TOPIC: Orange Rocker 30, combo, 2006
http://groups.google.com/group/sci.electronics.repair/t/fdf96ce609e107d9?hl=en
==============================================================================

== 1 of 4 ==
Date: Tues, Jun 29 2010 1:49 am
From: "Arfa Daily"

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:i0bgp3$f5c$1@news-01.bur.connect.com.au...
>
> "Arfa Daily"
>>
>> If it continues to cut out, a generator, a 'scope and a meter should tell
>> all. Valve circuits are very simple and very straightforward to trace
>> signals in, and troubleshoot.
>
> ** You don't service that many valve guitar amps - do you ??

Er, that would be a yes then ... Probably three or four a week, most every
week, and have been doing them for around 40 years ... Whilst some faults
are a little obscure, most are very straightforward, and I'm sure that you
don't have any more trouble fixing them, than I do Phil. I would pick a
fault on a valve amp over a transistor one, every time, as would probably
any engineer who has ever worked with valves. Every stage is pretty much
independent, and troubleshoot-able as a separate entity. You can't say that
about most transistor amps.

>
> The ones that were originally well made are now so old they have strange
> faults most techs have never seen before - while the ones made more
> recently have designed in faults never seen before by anyone.
>
> A few examples.
>
> 1. Recent Marshall combo amps with fibreglass PCBs that become LEAKY
> when hot - output valve bias goes crazy and even the phase splitter
> stage goes way out of DC balance in normal operation because of leakage
> from anode tracks to grid tracks. There is simply no fix for this
> problem.

Care to give me a model for that behaviour ? I see a lot of Marshall combos,
as they are built just a few miles from where I live. I have not seen any
similar problems here. I used to visit Jim Marshall in his factory in the
early days. He was a very good friend of a friend of mine. As to the problem
with a - g leakage, I would have thought that you might have been able to
get away with isolating the affected tracks by cutting or even removing them
from the board completely, and then hard wiring.

>
> 2. Recent Gibson /Trace Elliot amps that develop mysterious crackling
> noises all over the circuit due to the use of water soluble flux that was
> never properly washed of the PCB. Removing the main PCB entirely and
> washing it thoroughly in solvent is the only fix.
>
> 3. Same amps as above use 9 pin PCB mount sockets that SHRINK - yep,
> the plastic material used to make the socket shrinks under the heat from
> EL84s, reducing the pitch circle diameter so much it is impossible to fit
> a new tube in the socket. Replacing all the output valve sockets is the
> only fix.
>
> Then there are all the issues with the valves themselves - all new
> production now comes from China or the former USSR and most of the valves
> have designed in faults of kinds that were never seen previously. Eg.
> nearly all 12AX7s now crackle and pop if tapped with the back of a
> screwdriver and/or have bad heater cathode hum or are very microphonic -
> while octal power types often suffer from bad soldering (PbF ?) on the
> pins causing all manner of weird intermittents when the solder joint lets
> go.

Whilst I would agree that valve quality is not as good as it was when the
likes of Mullard and Brimar etc made them, I also don't think that they are
quite as bad as you seem to find them, if you buy decent quality ones, or
manufacturer's originals, which have been vetted by the amp manufacturer as
being of the required quality. The Ruby HG (Hi Grade) 12AX7s that I use,
don't crackle and pop, and are no more microphonic than any high gain
triodes have ever been. I also don't find the h - k leakage bad either -
certainly not enough to identify as being a predominant source of unwanted
hum. And as to bad soldering on octal base pins, I honestly can't say that
I've ever seen this problem on any amp that's been across my bench, or on
any replacement valves that I have fitted, which may have had their bases
connected to the leadouts by PbF. Perhaps I've just been lucky ...

>
> Yep - fixing valve amps is pure joy.
>
>
> .... Phil
>
>

Well, I find it so ...

Arfa

== 2 of 4 ==
Date: Tues, Jun 29 2010 5:32 am
From: "Phil Allison"

"Arfa Daily"
> "Phil Allison"
>>
>>> If it continues to cut out, a generator, a 'scope and a meter should
>>> tell all. Valve circuits are very simple and very straightforward to
>>> trace signals in, and troubleshoot.
>>
>> ** You don't service that many valve guitar amps - do you ??
>
>
> Er, that would be a yes then ... Probably three or four a week, most
> every week, and have been doing them for around 40 years ... Whilst some
> faults are a little obscure, most are very straightforward, and I'm sure
> that you don't have any more trouble fixing them, than I do Phil.

** I fix them all - of course.

But there is plenty of trouble with most of them.

> I would pick a fault on a valve amp over a transistor one, every time, as
> would probably any engineer who has ever worked with valves.

** Solid state gear is far easier to fix and make stay fixed - IM long E.

>> The ones that were originally well made are now so old they have strange
>> faults most techs have never seen before - while the ones made more
>> recently have designed in faults never seen before by anyone.
>>
>> A few examples.
>>
>> 1. Recent Marshall combo amps with fibreglass PCBs that become LEAKY
>> when hot - output valve bias goes crazy and even the phase splitter
>> stage goes way out of DC balance in normal operation because of leakage
>> from anode tracks to grid tracks. There is simply no fix for this
>> problem.
>
>
> Care to give me a model for that behaviour ?

** Yep - the JCM2000: TSL100 combo series.

Easy to find many stories about the same problem on usenet and web forums.

> I see a lot of Marshall combos, as they are built just a few miles from
> where I live. I have not seen any similar problems here. I used to visit
> Jim Marshall in his factory in the early days. He was a very good friend
> of a friend of mine.

** Nice guy - who never designed or built an amp in his life.

> As to the problem with a - g leakage, I would have thought that you might
> have been able to get away with isolating the affected tracks by cutting
> or even removing them from the board completely, and then hard wiring.

** Tried that idea with the very first example I ever came across.

The PCB wound up looking like a piece of Swiss cheese and still the problem
was not cured.

The only "treatment" that helped at all was to install a fan to keep the
valves and hence PCB cooler.

Colleagues have complained to me about the exact same problem.

> Whilst I would agree that valve quality is not as good as it was when the
> likes of Mullard and Brimar etc made them, I also don't think that they
> are quite as bad as you seem to find them, if you buy decent quality ones,
> or manufacturer's originals, which have been vetted by the amp
> manufacturer as being of the required quality.

** The BAD valves are already fitted in the amps that come to me for
service.

There are NO " manufacturers originals" available in Australia AFAIK.

> The Ruby HG (Hi Grade) 12AX7s that I use, don't crackle and pop, and are
> no more microphonic than any high gain triodes have ever been.

** Yaaawwwnnnnnn.....

You compare the particular with the general.

How tedious.

> I also don't find the h - k leakage bad either - certainly not enough to
> identify as being a predominant source of unwanted hum.

** How odd then that so many new generation valve amps use DC supply for
heaters JUST because of this issue.

> And as to bad soldering on octal base pins, I honestly can't say that I've
> ever seen this problem on any amp that's been across my bench,

** What planet do you live on ???

.... Phil

== 3 of 4 ==
Date: Tues, Jun 29 2010 8:59 am
From: "Arfa Daily"

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:i0cp5t$5t2$1@news-01.bur.connect.com.au...
>
> "Arfa Daily"
>> "Phil Allison"
>>>
>>>> If it continues to cut out, a generator, a 'scope and a meter should
>>>> tell all. Valve circuits are very simple and very straightforward to
>>>> trace signals in, and troubleshoot.
>>>
>>> ** You don't service that many valve guitar amps - do you ??
>>
>>
>> Er, that would be a yes then ... Probably three or four a week, most
>> every week, and have been doing them for around 40 years ... Whilst some
>> faults are a little obscure, most are very straightforward, and I'm sure
>> that you don't have any more trouble fixing them, than I do Phil.
>
>
> ** I fix them all - of course.
>
> But there is plenty of trouble with most of them.
>
>
>> I would pick a fault on a valve amp over a transistor one, every time, as
>> would probably any engineer who has ever worked with valves.
>
>
> ** Solid state gear is far easier to fix and make stay fixed - IM long
> E.
>
>
>
>>> The ones that were originally well made are now so old they have strange
>>> faults most techs have never seen before - while the ones made more
>>> recently have designed in faults never seen before by anyone.
>>>
>>> A few examples.
>>>
>>> 1. Recent Marshall combo amps with fibreglass PCBs that become LEAKY
>>> when hot - output valve bias goes crazy and even the phase splitter
>>> stage goes way out of DC balance in normal operation because of leakage
>>> from anode tracks to grid tracks. There is simply no fix for this
>>> problem.
>>
>>
>> Care to give me a model for that behaviour ?
>
>
> ** Yep - the JCM2000: TSL100 combo series.
>
> Easy to find many stories about the same problem on usenet and web forums.
>
>
>> I see a lot of Marshall combos, as they are built just a few miles from
>> where I live. I have not seen any similar problems here. I used to visit
>> Jim Marshall in his factory in the early days. He was a very good friend
>> of a friend of mine.
>
> ** Nice guy - who never designed or built an amp in his life.
>
>
>> As to the problem with a - g leakage, I would have thought that you might
>> have been able to get away with isolating the affected tracks by cutting
>> or even removing them from the board completely, and then hard wiring.
>
> ** Tried that idea with the very first example I ever came across.
>
> The PCB wound up looking like a piece of Swiss cheese and still the
> problem was not cured.
>
> The only "treatment" that helped at all was to install a fan to keep the
> valves and hence PCB cooler.
>
> Colleagues have complained to me about the exact same problem.
>
>
>
>> Whilst I would agree that valve quality is not as good as it was when the
>> likes of Mullard and Brimar etc made them, I also don't think that they
>> are quite as bad as you seem to find them, if you buy decent quality
>> ones, or manufacturer's originals, which have been vetted by the amp
>> manufacturer as being of the required quality.
>
>
> ** The BAD valves are already fitted in the amps that come to me for
> service.
>
> There are NO " manufacturers originals" available in Australia AFAIK.
>
>
>> The Ruby HG (Hi Grade) 12AX7s that I use, don't crackle and pop, and are
>> no more microphonic than any high gain triodes have ever been.
>
> ** Yaaawwwnnnnnn.....
>
> You compare the particular with the general.
>
> How tedious.
>
>
>> I also don't find the h - k leakage bad either - certainly not enough to
>> identify as being a predominant source of unwanted hum.
>
> ** How odd then that so many new generation valve amps use DC supply for
> heaters JUST because of this issue.
>
>
>> And as to bad soldering on octal base pins, I honestly can't say that
>> I've ever seen this problem on any amp that's been across my bench,
>
>
> ** What planet do you live on ???
>
>
>
> .... Phil
>

Apparently, a very different one from you ...

But then, of course, I was forgetting who I was trying to have a reasoned
discussion with. It had completely slipped my mind that anyone who looks at
anything from a different point of view to you, must be wrong. I suppose
you'll start in on the hysterical abuse hurling next. Well, if that's what
you need to do, go right ahead. I really don't care. And I suppose you know
Jim all the way from upside down land do you ?

Arfa
>

== 4 of 4 ==
Date: Tues, Jun 29 2010 12:24 pm
From: "Geoffrey S. Mendelson"

Arfa Daily wrote:
> Er, that would be a yes then ... Probably three or four a week, most every
> week, and have been doing them for around 40 years

If you are such an expert, please tell us how they got that volume
control to go to 11, while (whilst?) everyone knows they only go to 10?

:-)

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
I do multitasking. If that bothers you, file a complaint and I will start
ignoring it immediately.

==============================================================================
TOPIC: Notebook freezing when connected to external power supply
http://groups.google.com/group/sci.electronics.repair/t/5ce5b775904c6f5d?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, Jun 29 2010 2:37 am
From: Mike De Petris

On 8 May, 11:57, Mike De Petris <mikedepet...@gmail.com> wrote:
> On Apr 24, 9:48 pm, Mike De Petris <mikedepet...@gmail.com> wrote:
>
>
>
> > On Apr 24, 8:30 pm, Meat Plow <mhyw...@yahoo.com> wrote:
>
> > > On Fri, 23 Apr 2010 13:00:57 -0700 (PDT), Mike De Petris
> > > <mikedepet...@gmail.com>wrote:
>
> > > >I have a Toshiba Satellite A205 - S4777 that works perfect while on
> > > >battery, but the instance i plug the charger in, it freezes. First i
> > > >thought it was a Vista-Toshiba issue but only to discover that even in
> > > >BIOS it freezes instantly when the charger is plugged in. When the
> > > >laptop is off, any attempt to power it on while the charger is plugged
> > > >in, results only in a flicker of the power led.
> > > >I tried different chargers, ANY possible power options combinations in
> > > >Vista and Win7.
>
> > > >If I boot from battery and enter Windows Safe Mode, or Hiren's boot
> > > >CD, or WinXP mini all works fine even if I connect the power cord,
> > > >where normal Windows and BIOS freeze istantly.
>
> > > >I'm even thing of giving current directly by the battery contacts...
> > > >may this be possible?
>
> > > >Any help or advice on possible causes or solution to this issue would
> > > >be grateful. Thank you :)
>
> > > Uninstall the Toshiba Power Managemnt utility if you have it
> > > installed. If that fixes it try reinstalling it. If you don't have the
> > > utility installed go to Toshiba and see if it is available for your
> > > 205 and the Vista platform.
>
> > I have plain Windows 7 installed at the moment, no Toshiba nor other
> > utilities, even never connected to the network.
>
> > Anyway it freezes even in the BIOS when connecting power.
>
> don't know what more to check!

the laptop is still apart, had little time to experiment, the two
fuses are ok will have to test capacitors, in the while I took away
the cmos battery and soldered two wires to use a standard cr2032 but
nothing changes

my idea now, is that if I am not able to find the faulty component,
that may well be a custom one, I will try to cut the connections to
the battery poles and connect using a 2-way deviator, so that in one
position the lapton can work like now, charging the battery when
switched off, or running on battery only, or trun the deviator/switch
and give voltage directly to the cutted terminals, excluding the
battery, with an external power supply, the pc should still detect the
battery charge level from other contacts of battery in place

should this work?

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http://groups.google.com/group/sci.electronics.repair/t/bc2ebd4690007884?hl=en
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==============================================================================
TOPIC: Teac AG-790 has me stumped...
http://groups.google.com/group/sci.electronics.repair/t/19f1f1c9d95691fb?hl=en
==============================================================================

== 1 of 4 ==
Date: Tues, Jun 29 2010 6:59 am
From: "William R. Walsh"

Hi!

> So what does the cap do in the circuit ? Is it a big secret, or
> something ?

No, should it be? :-)

I don't know for certain what it does. I haven't explored it that
closely. I only noticed it being bloated out of the corner of my eye,
so I said "that should be replaced".

I've put it aside for now. Maybe another day.

TEAC has been no help. Although they did respond to my request asking
for more information, they recommended "shotgunning" the unit. (Yeah,
really.)

William

== 2 of 4 ==
Date: Tues, Jun 29 2010 9:26 am
From: "William R. Walsh"

Hi!

> Is it a double-sided (or worse - multilayer) pcb?

No, it appears to be a simple PCB with one layer on one side.

I would not call this receiver the greatest design I have seen.
Compared to the Sherwood and Sony receivers that I have been working
on, it strikes me as being unnecessarily complex. The main PCB is
littered with all sorts of components where the others are much
cleaner and simpler.

William

== 3 of 4 ==
Date: Tues, Jun 29 2010 9:36 am
From: "Arfa Daily"

"William R. Walsh" <wm_walsh@hotmail.com> wrote in message
news:4f83d666-93a0-4a06-8944-b4239971c92a@t10g2000yqg.googlegroups.com...
> Hi!
>
>> So what does the cap do in the circuit ? Is it a big secret, or
>> something ?
>
> No, should it be? :-)
>

Well, not really. I was just trying to find a way to better help you with
your diagnosis. Twice I had asked what the function of the cap was, and
twice you had not replied.

> I don't know for certain what it does. I haven't explored it that
> closely. I only noticed it being bloated out of the corner of my eye,
> so I said "that should be replaced".

Fair enough. A reasonable assumption, given the amount that's said on here
about bulging caps being at the bottom of many faults.

I assumed that as you had the service manual, and were engaged in fault
finding to component level, that you would have sufficient understanding of
circuit design to be able to just look at the cap on the schematic, and
determine its function without a second thought. It seems to me, pretty
fundamental to this process, that you know the function of the cap you have
replaced, considering that the fault symptoms changed dramatically after
replacing it. You seem to have put this down to coincidence, and indeed, it
may be, but from many long years of experience, it usually isn't. Either
something went wrong with the process of changing it - print damage,
component damage, via damage, un-noticed solder splat, etc, we've all been
there - or the fact that it was faulty before was masking some other
problem, that is now the dominant one. That was the reason that I felt it
important to know what the function of that cap is. I don't know how much
experience you have of component level faultfinding, but if it's not that
much, don't be afraid to admit that. There are plenty on here with a
lifetime's experience who will try their best to help, given the necessary
information, which ultimately helps others to learn.

>
> I've put it aside for now. Maybe another day

OK, no probs.

>
> TEAC has been no help. Although they did respond to my request asking
> for more information, they recommended "shotgunning" the unit. (Yeah,
> really.)
>
> William

It depends what they meant by "shotgunning". Once it has been determined
which stage a fault lies in, sometimes the best approach is to shotgun all
the electrolytics, or sometimes all the transistors. Semiconductors will
sometimes 'hide' their faultiness in that they've been weakened by obviously
failed nearby devices. This can - and does - result in bounced repairs,
sometimes with a cascade failure that you thought you'd successfully
repaired, repeated all over again ... :-(

So usually, if a manufacturer recommends "shotgunning", it's for a good
reason. Of course, whoever was replying to you might just have been being
facetious, and was actually suggesting that you stood it on a post at the
end of the yard, and took a 12 gauge to it .... :-))

Arfa

== 4 of 4 ==
Date: Tues, Jun 29 2010 10:37 am
From: Adrian C

On 27/06/2010 17:47, Arfa Daily wrote:

> Knowing that may be helpful to assess whether there may be an immediated
> connection between the previous and current symptoms, or whether we're
> in 'red herring' territory here ...

Well, I'm a bit bored at the moment so having a peek. :-)

The service manual is up on eserviceinfo. Page 13 is relevant.

http://www.eserviceinfo.com/downloadsm/25360/TEAC_AG-790.html

This (with the exception of the resistors) is all in output protection
past the final stage.

7C26 is in reverse series with 7C27 (i.e. non-polarised configuration)
and I guess may be short, open or leaky? Change it? What's across them
looks to be a summed fraction of the output of both L&R amplifiers, and
also a POW signal to the system micro.

The burning of the resistors first mentioned is indicative of an
overload prior to the final output transistors (7V19 to 7V22). Don't
know what that is all about, unless the amp power rails themselves have
been up to some silly voltage they shouldn't have been.

Seems enough discretes there to enjoy (!) a good troubleshoot, with
similar and isolate-able sections.

--
Adrian C

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==============================================================================
TOPIC: continuous action solder sucker
http://groups.google.com/group/sci.electronics.repair/t/1447a02166d89d01?hl=en
==============================================================================

== 1 of 3 ==
Date: Tues, Jun 29 2010 8:05 am
From: rush14

I'm attempting to fabricate a continuous action solder sucker along
the lines of those used at work

when repairing circuit boards. They were fast, clean, easy to use and
prevented damage to the circuit boards from excessive prolonged heat.

Unfortunately I'm now retired and the factory work has all been
outsourced overseas. There's nobody left now from work who would know
about this.

As I recall they consisted of a vacuum source (unknown to me), a
flexible hose connected to a small cylinder with a tuft of steel wool
inside to trap solder and a teflon sucking tip at the other end of
the cylinder.

Apparently there is more to vacuum technology than I imagined because
all my attempts have so far failed miserably. When I adapt a short
(~3 foot) flexible hose to my vacuum source the suction at the end of
the hose is almost non-existent.

My first attempt was using the air intake of a 12V automotive tire
inflator, an idea I got from extensive Google searching, although not
intended for that purpose. There seemed to be plenty of suction at the
air intake itself but almost no suction at the end of the flexible
hose.

I then decided to go to extremes and adapted the hose to the vacuum
port of a powerful shop vac. I actually expected the hose to collapse
from excessive vacuum but instead there was again almost no suction at
the end of the hose. I then added a secondary intake port to
alleviate what I thought might be excessive load on the shop vac then
tried using the shop vac exhaust port to create a vacuum. Neither
attempt worked.

I would normally give up but I know the theory behind it works from my
experience at the factory. I'm apparently ignorant in the physics of
vacuum.

I'm also familiar with other desoldering tools including plunger and
squeeze bulb solder suckers, solder wick and built in suckers on
soldering irons. I've found them all lacking in one way or another
compared to the gizmo I'm trying to imitate from the factory.

Any ideas from you guys about the error of my ways will be greatly
appreciated.

Thanks a bunch,
Rush

== 2 of 3 ==
Date: Tues, Jun 29 2010 8:46 am
From: "Arfa Daily"

"rush14" <rush14@columbus.rr.com> wrote in message
news:4014381d-7eea-4c0c-a2c3-72bbb46f7743@y4g2000yqy.googlegroups.com...
> I'm attempting to fabricate a continuous action solder sucker along
> the lines of those used at work
>
> when repairing circuit boards. They were fast, clean, easy to use and
> prevented damage to the circuit boards from excessive prolonged heat.
>
> Unfortunately I'm now retired and the factory work has all been
> outsourced overseas. There's nobody left now from work who would know
> about this.
>
> As I recall they consisted of a vacuum source (unknown to me), a
> flexible hose connected to a small cylinder with a tuft of steel wool
> inside to trap solder and a teflon sucking tip at the other end of
> the cylinder.
>
> Apparently there is more to vacuum technology than I imagined because
> all my attempts have so far failed miserably. When I adapt a short
> (~3 foot) flexible hose to my vacuum source the suction at the end of
> the hose is almost non-existent.
>
> My first attempt was using the air intake of a 12V automotive tire
> inflator, an idea I got from extensive Google searching, although not
> intended for that purpose. There seemed to be plenty of suction at the
> air intake itself but almost no suction at the end of the flexible
> hose.
>

My current Pace desoldering station uses a vacuum pump no larger than the
pressure pump used in a tyre inflator. My previous Weller DS900 had a
similar sized pump. On both of these stations, the vacuum port is connected
to the business end via about 2 feet of fairly soft and pliable
heat-resistant (silicone ?) tubing, about the size of TV coax. The vacuum on
both stations is as strong at the desoldering head as it is at the port, so
I'm not sure where you are having trouble with the physics of vacuum
engineering, with your attempts at replicating your work system. FWIW, there
are plenty of desoldering and rework stations on the market both new from
the Far East, and second hand on FleaBay. Most of the ones I've used work
pretty well, and in a non-production environment where there's only you, I
don't really see a need for continuous vacuum. Vacuum builds very quickly
when you operate the pump switch on a desoldering station, and is maintained
until you let go of the switch.

Arfa
> I then decided to go to extremes and adapted the hose to the vacuum
> port of a powerful shop vac. I actually expected the hose to collapse
> from excessive vacuum but instead there was again almost no suction at
> the end of the hose. I then added a secondary intake port to
> alleviate what I thought might be excessive load on the shop vac then
> tried using the shop vac exhaust port to create a vacuum. Neither
> attempt worked.
>
> I would normally give up but I know the theory behind it works from my
> experience at the factory. I'm apparently ignorant in the physics of
> vacuum.
>
> I'm also familiar with other desoldering tools including plunger and
> squeeze bulb solder suckers, solder wick and built in suckers on
> soldering irons. I've found them all lacking in one way or another
> compared to the gizmo I'm trying to imitate from the factory.
>
> Any ideas from you guys about the error of my ways will be greatly
> appreciated.
>
> Thanks a bunch,
> Rush

== 3 of 3 ==
Date: Tues, Jun 29 2010 8:46 am
From: "William Sommerwerck"

> I'm also familiar with other desoldering tools including plunger
> and squeeze bulb solder suckers, solder wick and built-in
> suckers on soldering irons. I've found them all lacking in one
> way or another compared to the gizmo from the factory I'm
> trying to imitate.

Do you really need a "continuous" device? Its only actual advantage is that
you simply hit the floor switch and "whoosh!" You don't have to reset the
plunger.

As nice as they are (and I've used them), I've never felt any strong need to
have one for occasional home use. Even if I could afford one, I wouldn't buy
one.

I have three hand-held units (two plastic EDSYNs, and an off-brand metal
unit). If a joint looks as if it's going to give me problems, I cock all of
them before I start. Solderwick has its own advantages, as it makes good use
of surface tension.

==============================================================================
TOPIC: JOBS&HOTPHOTOS
http://groups.google.com/group/sci.electronics.repair/t/f9c53727295e8f17?hl=en
==============================================================================

== 1 of 1 ==
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==============================================================================
TOPIC: See Hot Sexy Star Aishwarya Nude Bathing Videos In All Angles.
http://groups.google.com/group/sci.electronics.repair/t/e6103e5e905a9b8e?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, Jun 29 2010 9:28 am
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==============================================================================
TOPIC: So, who's the king of finding data sheets ... ?
http://groups.google.com/group/sci.electronics.repair/t/4e444c319ac55fa0?hl=en
==============================================================================

== 1 of 2 ==
Date: Tues, Jun 29 2010 10:03 am
From: "Arfa Daily"

I have a JVC hifi on my bench. Brand new, purchased by a British soldier
from a base somewhere else - possibly an American one, I seem to recall
being told. Oddly, for modern equipment, it has a voltage selector switch,
which was of course set to 120v, when he applied 240v UK power to it ...

The unit has a switch mode power supply (why though?) which is one of the
old style designs where the front end has two main filter caps, and the
input voltage is configured by how you jigger the connections of the reccy
and the caps. That is where the back panel voltage selector switch is
connected. Even more why though ? I would have thought that if you were
going to bother putting a switcher in a junky piece of hifi that was for
worldwide use, you would have used a design with an efficient PFC front end,
that makes it universal in terms of input voltage. Heaven knows, there's
enough cheap and cheerful examples out there, used by the million in LCD TV
sets.

Anyway, that aside, the bridge was twatted, as were two diodes?? , one
across each of the filter caps. These devices *look* like diodes, and the
symbol on the board is for a diode, and they're called D34 and D35, but I
can't recall having seen diodes in this position before. Voltage sharing
resistors, maybe. The type number on them is R4KL, and that's where the
problems start. All of the usual suspects - Datasheetarchive, Allicmall etc
deny knowing anything about this device. I can't seem to find any references
to the it on the net, other than lots of people on groups and forums, also
trying to find data. An admittedly brief trawl of some of those postings,
didn't seem to turn up any definitive answers. Some seem to be calling the
device a "transient suppressor" so maybe it's some kind of avalanche diode ?
Appears to be used in some monitors as well, so I'm surprised that it is so
difficult to turn up info.

Anyway, I've replaced the bridge, removed the short circuit
whatever-they-ares, and fired the supply up in isolation. It runs quite
happily without the "diodes" as you might imagine it would, and the output
voltages seem reasonable.

Apparently, the owner is being posted to Afghanistan or some such at the
weekend coming, and wants to take the hifi with him, so my back's against
the wall a bit on this one. In case of the remote possibility that anyone
has a service manual for the item, it's a JVC MX - KC68 or CA-MXKC68
depending on whether you have it listed by system or model number.

Any help then, please lads. TIA

Arfa

== 2 of 2 ==
Date: Tues, Jun 29 2010 10:50 am
From: "Vale"

"Arfa Daily" <arfa.daily@ntlworld.com> ha scritto nel messaggio
news:mHpWn.93263$tH4.24979@hurricane...
>I have a JVC hifi on my bench. Brand new, purchased by a British soldier
>from a base somewhere else - possibly an American one, I seem to recall
>being told. Oddly, for modern equipment, it has a voltage selector switch,
>which was of course set to 120v, when he applied 240v UK power to it ...

http://www.clubdediagramas.com/archivo/audio-equipos-de-musica-amplificadores-reproductores-etc-a7/jvc-m148/jvc-ca-mxkc68-manual-de-serviciopdf-f86697.html

Just register and download.
Spanish is not a problem, isn't it?

==============================================================================
TOPIC: Fire ants - computer bugs
http://groups.google.com/group/sci.electronics.repair/t/7eecdfe1b1971fbf?hl=en
==============================================================================

== 1 of 2 ==
Date: Tues, Jun 29 2010 10:56 am
From: JeffM

Jeff Liebermann wrote:
>carpenter ants[...]got into the TV antenna amplifier.
>Nothing was eaten, but they secreted some kind of acid,
>that ate the copper traces.
>
http://google.com/search?q=ants+formic-acid

Some birds have even figured out that squashed ants are useful.
http://google.com/search?q=ants+crows+formic-acid
There has been speculation that they get a buzz off this.

== 2 of 2 ==
Date: Tues, Jun 29 2010 11:28 am
From: Cydrome Leader

William R. Walsh <wm_walsh@hotmail.com> wrote:
> Hi!
>
>> Anyone have any operational experience of pc failure due to swarms
>> of fire ants ?
>
> Well, the circuit didn't fail and they weren't fire ants...but...
>
> I had a massive ants nest show up in an Optimus STA-795 stereo
> receiver. I noticed them moving around on the front panel, so I picked
> it up and WOW! Ants were pouring out of the bottom of the unit. The
> manual was underneath it, and they'd made some kind of a big white
> thing on top of it. I don't recall exactly what I did to evict them,
> but they never came back again.
>
> William

bugs seem to like heat, so things like vcrs were popular places for
roaches to live in.

you could tell from looking at a customer at the shop if you had to open
their electronics on newspapers and have a can of electronics cleaner
ready to kill anything that would run off.

==============================================================================

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