Maker Pro
Maker Pro

newbie solder question

D

Dave

Jan 1, 1970
0
I've been following the electronics newsgroups for some time, and decided to
try a small repair job. I have a 20Wx2 small single-board amplifier which
has only worked on one channel since it was given to me. Due to its' small
size, I'd like to repair it. Anyway, I used a DMM to test each of the 20 or
so electrolytic capacitors on the board. I know, I know, you can't really
test them in the circuit and expect a 100% accurate result. But as it's a
two-channel amp, I figured that at least the equivilant capacitors in
Channel A and Channel B should exhibit identical behavior.

I located two 470uF caps which differed in that one of them had zero
resistance which did not rise, even on the highest resistance scape of my
DMM, 20M ohm, as did all of the other caps. So, I figured I'd swap the two
identical caps (channel A and channel B). I tried using desoldering braid
(which I've used many times with great results) and found that the solder on
this board just wouldn't melt with my 30W iron. Well, says I , I'll just
use a bigger stick. I grabbed the 45W iron and still couldn't seem to melt
the solder through the braid, although the 45W iron WOULD melt the solder
directly. I heated each lead and wiggled and jiggled it loose. When I had
both caps removed I put the desoldering braid directly over the hole in the
PCB and with a pointed tip leaned on the board until the braid cleared up
the solder. This took maybe a minute or more of continuous heat.

When I removed the brad, AAAAGGGHH, it seems to have removed all of the
metal around the hole, not just the solder. Now the trace itself to which
the cap is connected is on the other side of the board and I could put in a
cap with slightly longer leads and solder it on the top. But if there's a
way to fix what I've done that'd be even better. When I put in the original
cap the solder just won't seem to go into the hole any more, it just sticks
to the iron.

Any advice greatly appreciated, I suppose this is how folks learn.

BTW, when I got both caps out they tested identically out of the circuit so
I'm pretty sure my problem is elsewhere. The circuit consists of a simple
power supply, unregulated, a whack of tiny (mainly 10uF 50V) electrolytic
caps, some mylar caps, resistors, a bass/treble IC, two 20W TO-220 amplifier
chips. I can very very faintly hear sound in the bad channel. When I turn
the volume up and down on the bad channel it makes a sort of "thumping"
sound from the bad speaker but doesn't amplify the sound. I've replaced the
amplfier chip on the bad channel as it was cheap and simple but this did not
help. Anybody have any suggestions what to check next? I do not own an
oscilloscope. I have checked and cleaned all of the knobs (bass, treble,
balance, volume), they all work as they're supposed to.

Thanks

Dave
 
M

Mike Berger

Jan 1, 1970
0
You often have to isolate components or parts of the circuit to
diagnose things anyway. Personally, I prefer a very hot temperature
controlled soldering iron and vacuum type solder sucker. Work fast
and don't let the heat travel beyond where you want it. I know
others prefer your method.

If you do lift a pad or trace, cut it with an exacto knife to keep
it from lifting any more and replace it with hookup wire wrapped
around the component leads and soldered to the edge of the broken
trace. If the traces are covered with a solder mask, you'll have
to scrape some of that away before you can solder.
 
G

GregS

Jan 1, 1970
0
I've been following the electronics newsgroups for some time, and decided to
try a small repair job. I have a 20Wx2 small single-board amplifier which
has only worked on one channel since it was given to me. Due to its' small
size, I'd like to repair it. Anyway, I used a DMM to test each of the 20 or
so electrolytic capacitors on the board. I know, I know, you can't really
test them in the circuit and expect a 100% accurate result. But as it's a
two-channel amp, I figured that at least the equivilant capacitors in
Channel A and Channel B should exhibit identical behavior.

I located two 470uF caps which differed in that one of them had zero
resistance which did not rise, even on the highest resistance scape of my
DMM, 20M ohm, as did all of the other caps. So, I figured I'd swap the two
identical caps (channel A and channel B). I tried using desoldering braid
(which I've used many times with great results) and found that the solder on
this board just wouldn't melt with my 30W iron. Well, says I , I'll just
use a bigger stick. I grabbed the 45W iron and still couldn't seem to melt
the solder through the braid, although the 45W iron WOULD melt the solder
directly. I heated each lead and wiggled and jiggled it loose. When I had
both caps removed I put the desoldering braid directly over the hole in the
PCB and with a pointed tip leaned on the board until the braid cleared up
the solder. This took maybe a minute or more of continuous heat.

When I removed the brad, AAAAGGGHH, it seems to have removed all of the
metal around the hole, not just the solder. Now the trace itself to which
the cap is connected is on the other side of the board and I could put in a
cap with slightly longer leads and solder it on the top. But if there's a
way to fix what I've done that'd be even better. When I put in the original
cap the solder just won't seem to go into the hole any more, it just sticks
to the iron.

Any advice greatly appreciated, I suppose this is how folks learn.

BTW, when I got both caps out they tested identically out of the circuit so
I'm pretty sure my problem is elsewhere. The circuit consists of a simple
power supply, unregulated, a whack of tiny (mainly 10uF 50V) electrolytic
caps, some mylar caps, resistors, a bass/treble IC, two 20W TO-220 amplifier
chips. I can very very faintly hear sound in the bad channel. When I turn
the volume up and down on the bad channel it makes a sort of "thumping"
sound from the bad speaker but doesn't amplify the sound. I've replaced the
amplfier chip on the bad channel as it was cheap and simple but this did not
help. Anybody have any suggestions what to check next? I do not own an
oscilloscope. I have checked and cleaned all of the knobs (bass, treble,
balance, volume), they all work as they're supposed to.

Thanks

Dave

You didn't mention measuring at the same points with caps removed.
I usually recompose circuit traces with solid conductor wire.
Probably at least a 50% chance the chip is bad.
Sometimes I have to double up on irons. I've also lit the Bic
next to the iron for more heat. My Radio Shack 250 watt gun for big jobs!

greg
 
M

Mr. Land

Jan 1, 1970
0
Give up using the braid...that stuff sucks (or, rather, it doesn't).
Get yourself a solder sucker if you're going to do stuff like this.

BTW, if I had an audio power amp that didn't work, I think the caps
would be near the end of my list of things to check. Start with the
power (aka output) transistors and work your way backwards. Unless
this is a really esoteric unit, both channels probably share the power
supply, so if one channel is working, you can probably assume that's OK.
 
D

Dave

Jan 1, 1970
0
Mr. Land said:
Give up using the braid...that stuff sucks (or, rather, it doesn't).
Get yourself a solder sucker if you're going to do stuff like this.
As I noted before I've used the braid quite a bit in the past and found it
to work well... but will pick up a sucker anyways as obviously I need it.
BTW, if I had an audio power amp that didn't work, I think the caps
would be near the end of my list of things to check. Start with the
power (aka output) transistors and work your way backwards. Unless
this is a really esoteric unit, both channels probably share the power
supply, so if one channel is working, you can probably assume that's OK.

I did start at the output transisters and replaced them all on the bad
channel (they're all on an integrated 20W amp chip, NS LM1875). I swapped
the caps in an effort to avoid trying to source a 10-year-old base/treble IC
which is likely the problem. Other than the output IC's, mixer IC, and
rectifier, there ain't a whole lot on the board except caps and resistors.
Resistors all checked out OK, move on to electrolytics... No?
 
D

Dave D

Jan 1, 1970
0
Dave said:
As I noted before I've used the braid quite a bit in the past and found it
to work well... but will pick up a sucker anyways as obviously I need it.

My general rule is a solder sucker for standard work and braid for smaller
or awkward tasks, especially certain surface mount work. A solder sucker is
far more appropriate for removing components like electrolytic caps from an
amp IMO.
I did start at the output transisters and replaced them all on the bad
channel (they're all on an integrated 20W amp chip, NS LM1875). I swapped
the caps in an effort to avoid trying to source a 10-year-old base/treble
IC
which is likely the problem. Other than the output IC's, mixer IC, and
rectifier, there ain't a whole lot on the board except caps and resistors.
Resistors all checked out OK, move on to electrolytics... No?

Do you still have a short? If so that makes things very easy- a short is
probably the easiest fault there is to diagnose. Simply trace the two PCB
tracks which are shorted and find all other components across these tracks.
One of them must be shorted out. Is the capacitor in question on the supply
rail? Check that the new IC you fitted doesn't have any solder bridges, and
if it has a mica heatsink insulator, make sure it's not damaged. I doubt
it's a shorted cap, but it is possible nonetheless.

It's possible the 470uF capacitor is part of the decoupled supply to the
preamp section, if so it may have a zener diode in parallel to give a
regulated supply. Therefore, check for shorted zeners.

The output ICs no doubt are coupled to the speakers via large electrolytic
capacitors, what is the voltage level on the IC side of this cap with
respect to ground? It should be close to half supply potential. Compare it
with the good side, but take care not to short anything out.

Are both output ICs getting a supply? Are they both getting a ground? Have
you measured voltage levels on each pin and compared them with the good
side? Have you downloaded a datasheet for the ICs, found the input pin and
injected a signal there to listen for output? Even touching a finger to the
input pin may give a buzz from the speaker, or a screwdriver may give a
click. There's ways and means, even without test equipment!

Dave
 
D

default

Jan 1, 1970
0
I've been following the electronics newsgroups for some time, and decided to
try a small repair job. I have a 20Wx2 small single-board amplifier which
has only worked on one channel since it was given to me. Due to its' small
size, I'd like to repair it. Anyway, I used a DMM to test each of the 20 or
so electrolytic capacitors on the board. I know, I know, you can't really
test them in the circuit and expect a 100% accurate result. But as it's a
two-channel amp, I figured that at least the equivilant capacitors in
Channel A and Channel B should exhibit identical behavior.

I located two 470uF caps which differed in that one of them had zero
resistance which did not rise, even on the highest resistance scape of my
DMM, 20M ohm, as did all of the other caps. So, I figured I'd swap the two
identical caps (channel A and channel B). I tried using desoldering braid
(which I've used many times with great results) and found that the solder on
this board just wouldn't melt with my 30W iron. Well, says I , I'll just
use a bigger stick. I grabbed the 45W iron and still couldn't seem to melt
the solder through the braid, although the 45W iron WOULD melt the solder
directly. I heated each lead and wiggled and jiggled it loose. When I had
both caps removed I put the desoldering braid directly over the hole in the
PCB and with a pointed tip leaned on the board until the braid cleared up
the solder. This took maybe a minute or more of continuous heat.

When I removed the brad, AAAAGGGHH, it seems to have removed all of the
metal around the hole, not just the solder. Now the trace itself to which
the cap is connected is on the other side of the board and I could put in a
cap with slightly longer leads and solder it on the top. But if there's a
way to fix what I've done that'd be even better. When I put in the original
cap the solder just won't seem to go into the hole any more, it just sticks
to the iron.

Any advice greatly appreciated, I suppose this is how folks learn.

BTW, when I got both caps out they tested identically out of the circuit so
I'm pretty sure my problem is elsewhere. The circuit consists of a simple
power supply, unregulated, a whack of tiny (mainly 10uF 50V) electrolytic
caps, some mylar caps, resistors, a bass/treble IC, two 20W TO-220 amplifier
chips. I can very very faintly hear sound in the bad channel. When I turn
the volume up and down on the bad channel it makes a sort of "thumping"
sound from the bad speaker but doesn't amplify the sound. I've replaced the
amplfier chip on the bad channel as it was cheap and simple but this did not
help. Anybody have any suggestions what to check next? I do not own an
oscilloscope. I have checked and cleaned all of the knobs (bass, treble,
balance, volume), they all work as they're supposed to.

Thanks

Dave
Well back in the "old days" we used "eyelets" - didn't have plated
through holes for circuit boards. The eyelets were just miniature one
part hollow rivets - or similar to grommets used in sails or
tarpaulins. That would be an ideal fix if you burnt the plating off.

Solder Wick for single sided boards - solder sucker for double sided
boards.

Regarding the amp. Have you checked the DC voltages between the
channels? Is this a single supply or plus and minus supplies? TO220 -
five lead power op amp? built in thermal, short circuit, and safe
operating area protection? I assume you only have one chip per
channel (or "bridged" with two chips per channel?)

If you can identify the chip and its input(S), you might try using a
capacitor to bridge signal from the working channel's input into the
input of the dead channel. (observing polarity if using an
electrolytic). Unplug the input to the dead channel while testing if
possible. The cap size will be 10 uf or less for a high impedance
audio stage input. That should localize the problem between the input
or output of the power amp chip.

If it is like the TO220's I'm using, there's a differential input
(inverting and non-inverting) inputs - make sure you drive the correct
one).

One assumes you switched speakers at some point.
 
D

Dave

Jan 1, 1970
0
Well back in the "old days" we used "eyelets" - didn't have plated
through holes for circuit boards. The eyelets were just miniature one
part hollow rivets - or similar to grommets used in sails or
tarpaulins. That would be an ideal fix if you burnt the plating off.
I think I'll solder to the trace on the other side of the board, just means
that the cap won't sit flush anymore but that's okay, lots of room in the
enclosure.
Solder Wick for single sided boards - solder sucker for double sided
boards.

Yes, must buy solder sucker. It's on my list now.
Regarding the amp. Have you checked the DC voltages between the
channels?

No. Do you mean between the channel A and channel B signal outputs with no
signal applied to the inputs? If there WAS a DC voltage differential what
might this tell me? Failed coupling cap? There are no output caps, the amp
output pin (see below) goes straight to the center pin of the RCA jack on
the back.
Is this a single supply or plus and minus supplies?

Both the amp and bass/treble/volume/balance IC's run off +Vcc.


TO220 -
five lead power op amp? built in thermal, short circuit, and safe
operating area protection? I assume you only have one chip per
channel (or "bridged" with two chips per channel?)
One chip per channel. They're LM1875T's, yes they have built-in thermal,
short circuit, etc. As I noted I have already replaced the one on the bad
channel (they are a TO-220 package).
If you can identify the chip and its input(S), you might try using a
capacitor to bridge signal from the working channel's input into the
input of the dead channel. (observing polarity if using an
electrolytic). Unplug the input to the dead channel while testing if
possible. The cap size will be 10 uf or less for a high impedance
audio stage input. That should localize the problem between the input
or output of the power amp chip.
Does it matter if I use an electrolytic or not? See pinout below, but I'd
connect pin 1 of channel A (working) to pin 1 of channel B (dead). If I do
use electrolytics, which end is positive, A or B? Why do I need to use a
capacitor to bridge as opposed to a wire?
If it is like the TO220's I'm using, there's a differential input
(inverting and non-inverting) inputs - make sure you drive the correct
one).
Here's the pinout:

1 +IN
2 -IN
3 -V(EE)
4 OUTPUT
5 V(CC)

From what I can see, pin 1 is signal in, pin 2 is used as the negative
feedback loop, being connected to pin 4 via a 20K resistor. There are no
coupling caps on the outputs.
One assumes you switched speakers at some point.
--

Yes, first thing I tried.
 
D

Dave

Jan 1, 1970
0
Dave D said:
Do you still have a short? If so that makes things very easy- a short is
probably the easiest fault there is to diagnose. Simply trace the two PCB
tracks which are shorted and find all other components across these tracks.
One of them must be shorted out. Is the capacitor in question on the supply
rail? Check that the new IC you fitted doesn't have any solder bridges, and
if it has a mica heatsink insulator, make sure it's not damaged. I doubt
it's a shorted cap, but it is possible nonetheless.
I checked for solder bridges on the new IC VERY carefully when I put it in,
as I did also inspect the mica insulator.
It's possible the 470uF capacitor is part of the decoupled supply to the
preamp section, if so it may have a zener diode in parallel to give a
regulated supply. Therefore, check for shorted zeners.
The balance/tone/volume IC (which is basically my entiere 'pre-amp section')
has a zener internally, BUT I see that it also uses an external decoupling
cap on the internally regulated voltage supply... must check which cap
performs this function.
The output ICs no doubt are coupled to the speakers via large electrolytic
capacitors, what is the voltage level on the IC side of this cap with
respect to ground? It should be close to half supply potential. Compare it
with the good side, but take care not to short anything out.
No, no output caps at all. Output pin of amp IC goes directly to RCA plug
via large trace.
 
A

Arfa Daily

Jan 1, 1970
0
Dave said:
I think I'll solder to the trace on the other side of the board, just
means
that the cap won't sit flush anymore but that's okay, lots of room in the
enclosure.


Yes, must buy solder sucker. It's on my list now.

No. Do you mean between the channel A and channel B signal outputs with
no
signal applied to the inputs? If there WAS a DC voltage differential what
might this tell me? Failed coupling cap? There are no output caps, the
amp
output pin (see below) goes straight to the center pin of the RCA jack on
the back.


Both the amp and bass/treble/volume/balance IC's run off +Vcc.


TO220 -
One chip per channel. They're LM1875T's, yes they have built-in thermal,
short circuit, etc. As I noted I have already replaced the one on the bad
channel (they are a TO-220 package).

Does it matter if I use an electrolytic or not? See pinout below, but I'd
connect pin 1 of channel A (working) to pin 1 of channel B (dead). If I
do
use electrolytics, which end is positive, A or B? Why do I need to use a
capacitor to bridge as opposed to a wire?

Here's the pinout:

1 +IN
2 -IN
3 -V(EE)
4 OUTPUT
5 V(CC)

From what I can see, pin 1 is signal in, pin 2 is used as the negative
feedback loop, being connected to pin 4 via a 20K resistor. There are no
coupling caps on the outputs.


Yes, first thing I tried.
All of the advice given so far regarding the fault, is good stuff. As far as
solder wick / solder sucker / desoldering stations go, it's horses for
courses. Contrary to what one of the posters said about solder wick "
sucking " ( or not ... ), in my experience, this is only the case when you
either buy cheap, or use the wrong size for the job. Buying cheap at radio
rallies, will just get you old stock, where the flux has gone off, and then,
it doesn't suck. Using a solder wick with too big a size, with an iron
that's too small tip wise, or power wise, results in insufficient heat
transfer to the joint, and then it doesn't suck.

A solder sucker is very good for medium sized joints, but there is a real
technique to using one well, and if you use it on a ' poor ' quality board,
it will readily suck the print off as well as the solder. There is a real
balance between getting enough heat into the joint to melt the solder to a
point where it will stay molten enough to be sucked cleanly off the board,
and not destroying the bonding between the copper and the substrate.

If you do get yourself a solder sucker, get a good one for which all parts
are available - nozzle, neoprene suction washer, circlip ( you'll lose it
! ) etc. Practice a lot on a scrap board to get the heat / time thing right.
Clean it out regularly, and don't buy cheap !!

Arfa
 
D

Dave

Jan 1, 1970
0
Arfa Daily said:
All of the advice given so far regarding the fault, is good stuff. As far as
solder wick / solder sucker / desoldering stations go, it's horses for
courses. Contrary to what one of the posters said about solder wick "
sucking " ( or not ... ), in my experience, this is only the case when you
either buy cheap, or use the wrong size for the job. Buying cheap at radio
rallies, will just get you old stock, where the flux has gone off, and then,
it doesn't suck. Using a solder wick with too big a size, with an iron
that's too small tip wise, or power wise, results in insufficient heat
transfer to the joint, and then it doesn't suck.

Well, my desolder braid is cheap and old, and PERHAPS a bit too thick for
the job, but it's worked well recently on similar-sized joints using the
same iron.
A solder sucker is very good for medium sized joints, but there is a real
technique to using one well, and if you use it on a ' poor ' quality board,
it will readily suck the print off as well as the solder. There is a real
balance between getting enough heat into the joint to melt the solder to a
point where it will stay molten enough to be sucked cleanly off the board,
and not destroying the bonding between the copper and the substrate.

If you do get yourself a solder sucker, get a good one for which all parts
are available - nozzle, neoprene suction washer, circlip ( you'll lose it
! ) etc. Practice a lot on a scrap board to get the heat / time thing right.
Clean it out regularly, and don't buy cheap !!
Thanks for the advice, have not used one before. Unfortunately where I live
there are very few stores which sell electronic parts and buying one off of
the internet generally costs twice as much when you get done with shipping
and taxes and the like.
 
A

Arfa Daily

Jan 1, 1970
0
Dave said:
Well, my desolder braid is cheap and old, and PERHAPS a bit too thick for
the job, but it's worked well recently on similar-sized joints using the
same iron.

Thanks for the advice, have not used one before. Unfortunately where I
live
there are very few stores which sell electronic parts and buying one off
of
the internet generally costs twice as much when you get done with shipping
and taxes and the like.
This is true. I used to use solder wick years ago, and it wasn't very good,
so I stuck to a solder sucker. Then, a few years ago, huge amounts started
appearing at rallies for like 1 UKP per reel, so I bought loads, as did
friends. It was crap. I then read an article in my national ham radio
journal about this, and it said that the reason that the stuff didn't work
was because even though it was housed in a basically airtight container,
over several years of storage, the oxygen in the atmosphere reacted with the
powder flux that it's impregnated with, and destroyed its fluxing
characteristics. Hence the reason that it had been dumped cheap on the
amateur market, as it was of no commercial value at all.

Soon after this disappointing experience, I had occasion to be in a fellow
professional's workshop, and saw him using some solder wick made by "
Multicore ", and was amazed at its efficacy, so I immediately ordered a
reel, and now always have some at the ready. It's not cheap at 30 UKP for a
30m reel ( about $48 ) but it lasts a long time. I also use a Weller vacuum
desoldering station, but that's too expensive for amateur use, unless one
can be picked up cheap on e-Bay.

Arfa
 
S

Smitty Two

Jan 1, 1970
0
Dave said:
I located two 470uF caps which differed in that one of them had zero
resistance which did not rise, even on the highest resistance scape of my
DMM, 20M ohm, as did all of the other caps. So, I figured I'd swap the two
identical caps (channel A and channel B). I tried using desoldering braid
(which I've used many times with great results) and found that the solder on
this board just wouldn't melt with my 30W iron. Well, says I , I'll just
use a bigger stick. I grabbed the 45W iron and still couldn't seem to melt
the solder through the braid, although the 45W iron WOULD melt the solder
directly. I heated each lead and wiggled and jiggled it loose. When I had
both caps removed I put the desoldering braid directly over the hole in the
PCB and with a pointed tip leaned on the board until the braid cleared up
the solder. This took maybe a minute or more of continuous heat.
Thanks

Dave

Liquid flux. If you solder, you need it. Liquid flux. If you desolder,
you need it. Liquid flux. Good solder braid is better than any sucker
I've ever used, with the exception of the heated, power suckers, which
are a tad pricy for the casual hobbyist. Liquid flux.

Did I mention liquid flux?

A minute of continuous heat? I'd recommend a better quality soldering
iron. You shouldn't be taking any longer than a second or two to solder,
and two or three to desolder, small components like that.

Also, get some liquid flux.
 
L

larry moe 'n curly

Jan 1, 1970
0
Dave said:
Well, my desolder braid is cheap and old, and PERHAPS a bit too thick for
the job, but it's worked well recently on similar-sized joints using the
same iron.

My experience with solder sucking bulbs and plungers has been a lot
worse than with braid, except when the joint had a huge amount of
solder, and even then I sometimes had to remove the final traces of
solder by using braid

I once used braid that was over 1/8" wide, and it was terrible because
it absorbed too much heat. 0.06" - 0.08" works best for me. I also
avoid braid that's tarnished (won't stick to solder) or coarse (not
enough surface area, probably low quality as well), and I keep the
soldering iron tip really clean and cut off used braid right away
because dangling braid just draws heat away from the joint. I cut it
even if it isn't full of solder because its flux has been ruined by the
heat, keeping it from stick to solder.

When solder won't melt into the braid, I add more solder to the joint
because it seems that factory solder has a higher melting point or some
kind of film over it.

I don't understand why 45W isn't enough heat, but some irons seem to
deliver more heat to their tips than others of the same watt rating do,
or they get weak with age. 35W has been enough for me with
single-layer boards, except on large copper areas, and 45W should be
able to do 2-layer boards or even the smaller components on multilayer
boards, even when the lead connects to the internal ground or voltage
plane (I normally use 50W).
 
R

Ray L. Volts

Jan 1, 1970
0
Dave said:
... I tried using desoldering braid
(which I've used many times with great results) and found that the solder
on
this board just wouldn't melt with my 30W iron. Well, says I , I'll just
use a bigger stick. I grabbed the 45W iron and still couldn't seem to
melt
the solder through the braid, although the 45W iron WOULD melt the solder
directly. I heated each lead and wiggled and jiggled it loose. When I
had
both caps removed I put the desoldering braid directly over the hole in
the
PCB and with a pointed tip leaned on the board until the braid cleared up
the solder. This took maybe a minute or more of continuous heat.

That's far too long to hold an iron to a joint.
Aside from using functional (i.e. quality) wicks, something you need to keep
in mind is tip cleaning and tinning.

http://www.inlandcraft.com/Uguides/tipcare.htm

As for wicks, I've tried lots of different brands and from my experience
Tech-Spray's Pro Wicks and Easy Braid's Quick Braids give the best bang for
the buck. I've never had a spool of Pro Wick fail me, even after many years
in storage. Quick Braid is a little less expensive, though both are priced
very reasonably. Pro Wick performs better, with a little quicker heating
and a faster solder draw. Avoid Pro's Tool wicks like the plague.

A good compromise between an expensive professional desoldering station and
a cheap solder sucker is one of the powered solder suckers. These have a
heated barrel like the desoldering station guns and a simple vacuum chamber
like the inexpensive solder suckers. The wattage of these irons is
typically 30-45W. They can be had for around $20-$30US.
 
G

GregS

Jan 1, 1970
0
Liquid flux. If you solder, you need it. Liquid flux. If you desolder,
you need it. Liquid flux. Good solder braid is better than any sucker
I've ever used, with the exception of the heated, power suckers, which
are a tad pricy for the casual hobbyist. Liquid flux.

Did I mention liquid flux?

A minute of continuous heat? I'd recommend a better quality soldering
iron. You shouldn't be taking any longer than a second or two to solder,
and two or three to desolder, small components like that.

Also, get some liquid flux.

I would not be without my flux pen.

I never tried to make some. Just alcohol and regular
flux.

greg
 
J

jakdedert

Jan 1, 1970
0
GregS said:
I would not be without my flux pen.

I never tried to make some. Just alcohol and regular
flux.

greg
BTW, one use for the flux--I use the paste stuff, must try the
liquid--is to 'activate' old desoldering braid. When doing a lot of
work on old boards, I keep the tin of flux open, heat the braid and dip
the end into the flux between uses. It activates the braid and makes
for much easier desoldering.

Is that also the way to use the liquid stuff? It would probably be a
less messy than my procedure.....

jak
 
G

GregS

Jan 1, 1970
0
BTW, one use for the flux--I use the paste stuff, must try the
liquid--is to 'activate' old desoldering braid. When doing a lot of
work on old boards, I keep the tin of flux open, heat the braid and dip
the end into the flux between uses. It activates the braid and makes
for much easier desoldering.

Is that also the way to use the liquid stuff? It would probably be a
less messy than my procedure.....

jak

right!
 
M

Mr. Land

Jan 1, 1970
0
So, Dave...

This topic seems to have drifted off of the subject of helping you
troubleshoot your amp and onto desoldering techniques and tools...(not
that that isn't great content).

So have you fixed it?

If not, what's this 10-year-old mixer IC you mention? Do you have a
pinout of it? How do the DC voltages on all the pins of the output IC
compare? If you have a meter-based meter (was that redundant?), can
you see any DC fluctuation on the input or output pins of the output
IC's when you spin the volume control? Check both channels and compare
them.

I've seen speaker "thumping" occur when DC was getting to an input it
shouldn't be.
 
D

Dave

Jan 1, 1970
0
So have you fixed it?

Um, not yet. As you noted below, I also thought about DC getting to the
speakers being the cause of the thumping. That's what started me on my
capacitor-testing adventure in the first place. Which led to my frying the
PCB traces trying to remove the caps and associated solder with solder
braid. So I've got to procure a new pair of 470uF caps (with nice long
leads) that I can solder onto the other side of the board. After (hmm,
maybe at the same time) I procure a solder sucker and some new
decent-quality solder braid and some liquid flux (from other posters) to
clean up the mess I've made. I see that there is quite a bit of technique
involved with this de-soldering stuff... I'll get there.

The IC in question is an LM1036N, combo volume/tone/balance control. It's
available from Digikey for <$5, maybe I'll just order one for the price of a
Big Mac and fries, get my caps and assorted tools too. When I get the caps
back in I'll bridge one amp IC's input to the other one (via a 10uF cap
according to another poster perhaps to limit any DC voltage from getting
from the "bad" channel to the "good" and wreaking havoc there). This should
at least tell me if the output stage is working correctly. I guess I should
check input voltages at both op-amp IC's to make sure the bad channel is
being powered first. As I noted I've already replaced the bad channel's
output stage (LM1875T 20W amp TO-220). I've already tested all of the
diodes and resistors and (to the extent that they can be tested in-circuit)
caps with a DMM (not the best test but will show if a cap is open circuit or
shorted).

If not, what's this 10-year-old mixer IC you mention? Do you have a
pinout of it? How do the DC voltages on all the pins of the output IC
compare? If you have a meter-based meter (was that redundant?), can
you see any DC fluctuation on the input or output pins of the output
IC's when you spin the volume control? Check both channels and compare
them.
I didn't think of using an analog meter, that's a good way to roughly
compare outputs... I'll make up a CD with continuous tones to feed a signal
via the unit's RCA inputs and test the signal at various points moving
backwards from the output stage. I have a feeling it's the combo
volume/tone/balance IC but then I had a feeling it was the amp too and it
ain't.... I think I suffer from "jump to unsubstantiated conclusion"
syndrome and I just have to slow down and think things through before
running off to the store to replace another part.

I'll keep folks updated (a retain-my-pride way of saying "I'll likely have
more questions") via this thread.

Thanks for your help so far...

Dave
 
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