Need desoldering advice

hears fine, but

Those were/are common failure points. Any recent lightning in your area that may relate to the time of failure? I replaced a lot of 1488 and 1489 (receiver) after lightning storms in another life. Quite often you can just measure the voltage on the suspect port (pin) and compare it to a known good one. The bad one will quite often have a much different value. While powered up of course and a scope in DC mode works best. Expect to see negative (less than zero) voltages too.

A Soldapullit works well and no need to clip leads off. If you aren't careful clipping leads can mess up the circuit board too. Sockets can sometimes be helpful, sometimes not. Judgment call IMO.

Soldapullit:

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You can get these in lots of places. Get the deluxe/big model. The smaller ones don't work as well.

If you were closer by I would give you a new IC. Still have some stashed somewhere in my piles of stuff :)

Reply to
Leon Fisk
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That is a excellent link for more than just desoldering.

Thanks,

Wes

Reply to
clutch

That depends on several things.

1) Quality of socket. (A socket with machined pins grips better than any of the sockets with pins bent up from flat metal, and some of the bent ones grip better than others.) 2) Number of pins. The more pins, the better the grip of the socket on the chip. 3) The amount of vibration to which the board is subjected. If there is a lot of vibration, there is a greater chance of the chip walking out of the socket. Examples of poor places to use sockets would include control logic boards for CNC machines, automotive boards (especially racecar boards), and pinball machines with real pinballs and flippers. The ones which are purely logic and displays are a different matter, as long as the users don't keep trying to "tilt" them anyway. :-) 4) The mass of the chip. An example would be the old TRW 16x16 bit multiply chip with an integral heat sink -- this would be more likely to walk out of a socket than say a Motorola MC68000 CPU chip, which does not have the extra mass of the heatsink.

I forget what the board came from -- if it was even mentioned at the beginning of the thread.

I would probably make a tradeoff decision based on how likely subsequent failures of the chip were compared to the amount of vibration to which it would be subjected. It is possible to include clamp-down hardware to overcome the vibration walk-out problem.

Another factor would be the cost to replace the board -- because having to unsolder and replace chips multiple times in a single location on a board increases the chances of damaging the board -- and lacking a diagram showing which pins connect to where (thus allowing external jumpers to replace a failed internal trace -- if the speed is not too high for this to be practical) would tilt my choices towards the socket.

Enjoy, DoN.

Reply to
DoN. Nichols

Ive found that a tiny drop of Super Glue on an opposed set of leads tends to keep chips from walking, and is easily removed with a touch from a soldering pencil

gunner

Reply to
Gunner Asch

Reply to
Bob in Phx

Hmm ... an interesting idea. Thanks.

Enjoy, DoN.

Reply to
DoN. Nichols

I was desperate to keep MC-2 card socketed chips in their nests on Omniturns running bar feeders with no liners.

Been working pretty good now for about 8 yrs since I first tried it.

Gunner

Reply to
Gunner Asch

I've used RTV style silicone, hot glue (just a dab) and the way some sockets area made you can slip a small wire tie through underneath.

The bigger problem I've had with sockets is just poor connections that occur over time. Equipment develops a strange intermittent problem. Pull/rock the chip in its socket (chip was still fully seated) and the problem goes away for awhile. Those problems where always a lot of fun to troubleshoot/fix :(

Reply to
Leon Fisk

Bullshit! SMD devices are much easier to rework than through hole. I have removed & replaced 288 pin MPU chips with solder wick, a couple drops of Kester 1544 RMA liquid rosin flux, and an common Edsyn Loner soldering iron. The chip was installed 90 degrees off, so I removed most of the solder from the leads, then used a small curved pick and the edge of the soldering iron's tip to heat each pin, near the body. When it was hot enough it would pop loose from the pad. By the time you removed the iron and pick, it had cooled, so I moved to the next pin. All it takes is good eyesight, and steady hands. Soldering it back was even faster. A drop of the flux down each side, and tack opposite corners, then run a drop of solder down each row. Any excess was still on the tip when each row was finished. For bad SMD resistors and capacitors, a pair of irons made quick work of removal, and replacement. You work fast, to eliminate heat damage, and a pair of irons makes the surface tension properly center the new part on the pads.

The only 'Special tool'' I used was a stereo microscope, since my vision is so poor. I would have needed it for a lot of through hole rework, as well.

Reply to
Michael A. Terrell

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