Desoldering SOIC Chips

[Madness]

I've got an Apex 660 DVD player that I'm trying to repair. It's has very
low analog sound output (that is, you have to turn the TV all the way up
just to hear the sound). There's a separate circuit board that contains
the A/V outputs and associated circuitry.

I'm pretty sure that the two little JRC4580 op-amps on the board are the
problem. Trouble is: They're these little 4x4 SOIC chips soldered to the
BOTTOM of the board (whereas everything else on the top are conventional
through-board components). I found out via Mouser that the LM833 is an
equivelent that can replace the 4580.

My question is: How exactly does one desolder these things? Should I put
the board in the oven like that dude about a dozen posts up did w/ a
video card (I did get a bit of a laugh out of that)? Currently, I've
replaced all the electrolytics and a few transistors (S8050, 9014,
9015), but the problem still remains, which leads me to suspect the chips.

 

[jay]

I've got an Apex 660 DVD player that I'm trying to repair. It's has very
low analog sound output (that is, you have to turn the TV all the way up
just to hear the sound). There's a separate circuit board that contains
the A/V outputs and associated circuitry.

I'm pretty sure that the two little JRC4580 op-amps on the board are the
problem. Trouble is: They're these little 4x4 SOIC chips soldered to the
BOTTOM of the board (whereas everything else on the top are conventional
through-board components). I found out via Mouser that the LM833 is an
equivelent that can replace the 4580.

My question is: How exactly does one desolder these things? Should I put
the board in the oven like that dude about a dozen posts up did w/ a
video card (I did get a bit of a laugh out of that)? Currently, I've
replaced all the electrolytics and a few transistors (S8050, 9014,
9015), but the problem still remains, which leads me to suspect the chips.

Use a fine tip soldering iron, desolder 1 pin at a time and then lift
the pin up using a sharp needle or something similar, work on all the
pins and this way you will free the IC without damaging any of the
traces, of course your IC can no longer be used so if you still want to
reuse it you will probably need to heat the area with a heat gun.

If you want to go the heat gun route protect the surrounding areas with
a thick cardboard/plastic mask and then let the IC fall off once heated.

 

[Madness]

Use a fine tip soldering iron, desolder 1 pin at a time and then lift
the pin up using a sharp needle or something similar, work on all the
pins and this way you will free the IC without damaging any of the
traces, of course your IC can no longer be used so if you still want to
reuse it you will probably need to heat the area with a heat gun.

If you want to go the heat gun route protect the surrounding areas with
a thick cardboard/plastic mask and then let the IC fall off once heated.

What type of iron would you recommend? I don't think my $12 RatShack one
is going to work since it has a wide conical tip. One w/ a needle tip? I
don't need to worry about reusing the old chips since I ordered and
received the replacements from Mouser. Just that I get them off without
taking the solder pads w/ them.

 

[James Sweet]

What type of iron would you recommend? I don't think my $12 RatShack one
is going to work since it has a wide conical tip. One w/ a needle tip? I
don't need to worry about reusing the old chips since I ordered and
received the replacements from Mouser. Just that I get them off without
taking the solder pads w/ them.

That iron should work fine, it's not so much the tools but the skill and
patience of the person using them that matters. I've used a heat gun to
desolder chips too.

 

[Arfa Daily]

That iron should work fine, it's not so much the tools but the skill and
patience of the person using them that matters. I've used a heat gun to
desolder chips too.

If you take a piece of thin single strand wire, such as rework wire, thread
it through behind the pins, and tack solder its end to any convenient solder
point nearby, you can then pull the long end outwards away from the pins,
keeping it as flat to the board as you can. Then touch the first pin that's
holding the wire from moving, with the tip of your iron. So if you're right
handed, with the row of pins that you are desoldering facing away from you,
you will have threaded the wire through from left to right, and tacked its
right end down. You will now have the free left end in your left hand, and
the soldering iron in your right hand. As the joint melts, and wait a second
or two so that it has *thoroughly* melted, pull a little harder on the wire.
It will slide out from under the pin, taking any solder with it, and will
also lift the pin very slightly clear of the pad. Repeat for each pin until
the wire comes free from under the last pin, then repeat for the other side.
If the IC looks like it's on the move as you unsolder the other side, stop
when you get to the last pin, and just heat that one whilst lifting the
device off the board with tweezers. If the chip remains fixed to the board
by glue, then unsolder all of the pins with the wire, then use an old
scalpel to get in under the chip, and twist to break the glue seal.

Before fitting the new chip, you must remove any glue fragments from the
board, and you must carefully remove as much as possible of the original
solder from the pads, using a good quality de-solder braid. Place the new IC
as accurately as you can, then tack one corner pin, using as little solder
as you can. Now carefully examine your positioning to make sure that *all*
legs line up correctly with their pads. Adjust if necessary. It is now
pretty much essential to run some liquid flux in around all the pins, before
soldering them with a clean fine tipped iron, and fine gauge solder. After
doing this, I would strongly recommend cleaning the whole area with a
defluxing agent, and then examining your work with a strong magnifier, or
better, a jeweller's loupe.

For what it's worth, I actually think that replacing the ICs is highly
unlikely to cure your problem. Before going down this route, have you
checked *very* carefully that there is not a menu setting that disables the
PCM audio analogue mixdown ? Such a setting may be several layers down in
audio or system setup. Failing this, have you checked that the IC's have
both a positive and negative supply on them ( pins 4 and 7 from memory, but
check this ) ? There are several makes and models that suffer from the
symptoms that you have described, and the problem is that one or other of
the rails to the output buffer opamps, is missing. It is usually caused by a
short circuit rail decoupling capacitor, and the only aspect of operation of
the machine that's affected, is the analogue audio. If one of the rails is
missing, look for a couple of caps, probably something like 47uF or 100uF,
nearby the IC's.

Arfa

 

[Arfa Daily]

If you take a piece of thin single strand wire, such as rework wire,
thread it through behind the pins, and tack solder its end to any
convenient solder point nearby, you can then pull the long end outwards
away from the pins, keeping it as flat to the board as you can. Then touch
the first pin that's holding the wire from moving, with the tip of your
iron. So if you're right handed, with the row of pins that you are
desoldering facing away from you, you will have threaded the wire through
from left to right, and tacked its right end down. You will now have the
free left end in your left hand, and the soldering iron in your right
hand. As the joint melts, and wait a second or two so that it has
*thoroughly* melted, pull a little harder on the wire. It will slide out
from under the pin, taking any solder with it, and will also lift the pin
very slightly clear of the pad. Repeat for each pin until the wire comes
free from under the last pin, then repeat for the other side. If the IC
looks like it's on the move as you unsolder the other side, stop when you
get to the last pin, and just heat that one whilst lifting the device off
the board with tweezers. If the chip remains fixed to the board by glue,
then unsolder all of the pins with the wire, then use an old scalpel to
get in under the chip, and twist to break the glue seal.

Before fitting the new chip, you must remove any glue fragments from the
board, and you must carefully remove as much as possible of the original
solder from the pads, using a good quality de-solder braid. Place the new
IC as accurately as you can, then tack one corner pin, using as little
solder as you can. Now carefully examine your positioning to make sure
that *all* legs line up correctly with their pads. Adjust if necessary. It
is now pretty much essential to run some liquid flux in around all the
pins, before soldering them with a clean fine tipped iron, and fine gauge
solder. After doing this, I would strongly recommend cleaning the whole
area with a defluxing agent, and then examining your work with a strong
magnifier, or better, a jeweller's loupe.

For what it's worth, I actually think that replacing the ICs is highly
unlikely to cure your problem. Before going down this route, have you
checked *very* carefully that there is not a menu setting that disables
the PCM audio analogue mixdown ? Such a setting may be several layers down
in audio or system setup. Failing this, have you checked that the IC's
have both a positive and negative supply on them ( pins 4 and 7 from
memory, but check this ) ? There are several makes and models that suffer
from the symptoms that you have described, and the problem is that one or
other of the rails to the output buffer opamps, is missing. It is usually
caused by a short circuit rail decoupling capacitor, and the only aspect
of operation of the machine that's affected, is the analogue audio. If one
of the rails is missing, look for a couple of caps, probably something
like 47uF or 100uF, nearby the IC's.

Arfa

Senior moment !! Make that pins 4 and 8 ...

Arfa

 

[3T39]

Hello, Madness!
You wrote on Fri, 22 Sep 2006 22:29:13 GMT:

What type of iron would you recommend? I don't think my $12 RatShack one
is going to work since it has a wide conical tip. One w/ a needle tip? I
don't need to worry about reusing the old chips since I ordered and
received the replacements from Mouser. Just that I get them off without
taking the solder pads w/ them.


What I sometimes do is take a few inches of solid copper, fairly heavy guage
wire, and wind it around the element and tip of my old weller 25W soldering
iron. Wind it around about half a dozen times leaving a short length
extending from the tip. Cut the end into a chisel point and clean and tin it
with solder. I find this a useful tool for fine work if you don't do enough
SM stuf to justify a proper station. You can use finer wire of course to
make an even smaller point but on the smaller scales the surface tension of
the molten solder becomes a problem.


With best regards, 3T39. E-mail: [email protected]

 

[David Nebenzahl]

3T39 spake thus:

Hello, Madness!
You wrote on Fri, 22 Sep 2006 22:29:13 GMT:

What type of iron would you recommend? I don't think my $12 RatShack one
is going to work since it has a wide conical tip. One w/ a needle tip?

*Any* soldering iron will work. I get mine at those Chinese dollar
stores for, yep, $1. You know, you can file the tip to any shape you
like. You're not stuck with shape of the tip as sold.


--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.

- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)

 

[Arfa Daily]

3T39 spake thus:


*Any* soldering iron will work. I get mine at those Chinese dollar stores
for, yep, $1. You know, you can file the tip to any shape you like. You're
not stuck with shape of the tip as sold.

Hi David

That used to be a lot truer in the old days when the tips were made of
copper, but now that they are all iron clad or nickel plated, I find that
taking a file to them results in their rapid demise, especially with the
more aggressive fluxes that they are having to put in the lead-free crap
solder to make it stick to anything ...

Probably not so much of a problem if you are a hobbyist who takes his iron
out once a month, uses it for 5 minutes, and shuts it off again, but
definitely is if your irons are on 12 or more hours a day, as mine are.

Arfa

 

[David Nebenzahl]

Arfa Daily spake thus:

That used to be a lot truer in the old days when the tips were made of
copper, but now that they are all iron clad or nickel plated, I find that
taking a file to them results in their rapid demise, especially with the
more aggressive fluxes that they are having to put in the lead-free crap
solder to make it stick to anything ...

So, what a guy would want to do, maybe, is replace his tip with a piece
of copper bus bar or ground rod, say? Would that be better?

Probably not so much of a problem if you are a hobbyist who takes his iron
out once a month, uses it for 5 minutes, and shuts it off again, but
definitely is if your irons are on 12 or more hours a day, as mine are.

I'm definitely in the first category. Maybe once-three times a week.


--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.

- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)

 

[Arfa Daily]

Arfa Daily spake thus:


So, what a guy would want to do, maybe, is replace his tip with a piece of
copper bus bar or ground rod, say? Would that be better?


I'm definitely in the first category. Maybe once-three times a week.

You're probably OK then. I doubt that filing down would have much impact on
your tip life that you were bothered about. I used to prefer tips when they
were all copper, as when they did oxidise up, you could indeed just file 'em
up to a new tip shape, and re-tin. I used to use an old Adcola years ago,
that employed pure copper tips, and you used to be able to use and file
until you were down to like a half inch long, before you had to replace.

These days, I keep replacement tips for all of my irons in stock. I suppose
that I shouldn't imply that there's anything wrong with iron clad tips per
se. Initially, they definitely provide a ready-tinnable tip for much longer
than the all-copper ones did. But once they start to go, and stop tinning,
for sure you can get them back by lightly filing, but you'll then find that
inside a couple of days ( of 12 hours a piece ) you've got a dirty great
crater in the tip, and there's no option but to replace. Most of the irons
that I use are thermostatically controlled, so I would guess that the tip
design and materials, are carefully selected by the manufacturers to produce
a good tight control loop, and subbing for copper rod or whatever, would
probably not do the performance any favours. In fact, it might be quite hard
to do these days anyway, because most tips have particular shaped bodies to
fit their intended irons, but if you are just an occasional user, with an
iron that uses the sqeeze up collar type of tip mount, then you might well
find that you prefer a home-made all copper tip to the one originally
fitted.

Arfa