Re: Computer motherboard repair soldering

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YankeeTarheel wrote: Mon Mar 01, 2021 12:34 pm
Sometimes, if you're lucky, the circuit board will have a "+" and "-" printed on it, along with other data.
It was point-to-point wiring in an old SBE Model 34 transceiver - circa 1965, neat little rig, but tightly packed components. The built-in power supply has inputs for both 110VAC and 12VDC - a trivia point about them was that Barry Goldwater had one installed in his car for mobile use.

(I need to find someone skilled in working on them - the receiver works beautifully, but the transmitter side goes into oscillation, and I'm not savvy enough to find the problem...)

Re: Computer motherboard repair soldering

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Taking a picture of the orientation is a good idea if we don't have schematics, which is probably going to be the case with computer motherboards. I do this any time I'm doing an automotive (electrical) repair that I haven't done enough times to have memorized.
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Re: Computer motherboard repair soldering

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Heretic wrote: Sun Feb 28, 2021 9:24 pm Oh, yes - a simple thing, but easy to overlook...

Don't install the new electrolytic caps backward.

I did this once on a power supply for a tube-type Ham radio transceiver; my cat was not amused by an exploding capacitor, vacating the area at high speed.
Did he leave shit stains on the way out???
""If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you." -- LBJ

Re: Computer motherboard repair soldering

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I agree with CowboyT’s suggestion of taking a photo to help with orientation of the capacitor and stuff.

Is what you are replacing a surface-mount capacitor:
Image
...or the regular kind that sits above the board on the two long legs?


For surface mount ones where you can’t easily heat the solder to disengage, I recomend grabbing the old capacitor with a needle-nose plier and twist off while pushing DOWN into the board, NOT pulling up. I’ve messed up too many contacts on circuitboards trying to pull them up and off after trying to heat up the solder underneath. I find it is simpler and safer to break both legs off the capacitors with a gentle twisting motion to protect the board when solder is still cold. Then clean the old solder and the broken capacitor “legs” off the board afterwards.

There are tricks to soldering on surface mount capacitors too. But I’ll leave that for later if in fact that is what you are replacing.

Normal capacitors are much simpler to deal with.

Also seriously consider practicing the procedure a few times on a scrap circuit board from a dead VCR or something. Don’t do your first try on the important motherboard!
"It is better to be violent, if there is violence in our hearts, than to put on the cloak of non-violence to cover impotence. There is hope for a violent man to become non-violent. There is no such hope for the impotent." -Gandhi

Re: Computer motherboard repair soldering

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It’s the regular two prong kind. It’s why I’m fairly confident I can tackle the job. I’ll be buying some old similar boards with capacitors. I may try to find new capacitors if they are available. Yes, I will practice on the sacrificial boards first.
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"Resistance is futile. You will be assimilated!" Loquacious of many. Texas Chapter Chief Cat Herder.

Re: Computer motherboard repair soldering

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sikacz wrote: Sat Apr 17, 2021 7:24 pm It’s the regular two prong kind. It’s why I’m fairly confident I can tackle the job. I’ll be buying some old similar boards with capacitors. I may try to find new capacitors if they are available. Yes, I will practice on the sacrificial boards first.
As long as the capacitance is same as the bad one and the voltage rating is at least as high, you should be fine. If you wire 2 caps in parallel each with half the capacitance, but the correct voltage, you should get the same performance, but it's better to have the right size.

I don't know if silver soldering will help, but it can't hurt. I know that sweating pipes is a very different soldering exercise than electronics, having done both.
""If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you." -- LBJ

Re: Computer motherboard repair soldering

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YankeeTarheel wrote: Sat Apr 17, 2021 7:56 pm
sikacz wrote: Sat Apr 17, 2021 7:24 pm It’s the regular two prong kind. It’s why I’m fairly confident I can tackle the job. I’ll be buying some old similar boards with capacitors. I may try to find new capacitors if they are available. Yes, I will practice on the sacrificial boards first.
As long as the capacitance is same as the bad one and the voltage rating is at least as high, you should be fine. If you wire 2 caps in parallel each with half the capacitance, but the correct voltage, you should get the same performance, but it's better to have the right size.

I don't know if silver soldering will help, but it can't hurt. I know that sweating pipes is a very different soldering exercise than electronics, having done both.
The silver solder is for my wife's jewelry repair! LoL. I have another solder for electrical.
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Image

"Resistance is futile. You will be assimilated!" Loquacious of many. Texas Chapter Chief Cat Herder.

Re: Computer motherboard repair soldering

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sikacz wrote: Sat Apr 17, 2021 8:05 pm
YankeeTarheel wrote: Sat Apr 17, 2021 7:56 pm
sikacz wrote: Sat Apr 17, 2021 7:24 pm It’s the regular two prong kind. It’s why I’m fairly confident I can tackle the job. I’ll be buying some old similar boards with capacitors. I may try to find new capacitors if they are available. Yes, I will practice on the sacrificial boards first.
As long as the capacitance is same as the bad one and the voltage rating is at least as high, you should be fine. If you wire 2 caps in parallel each with half the capacitance, but the correct voltage, you should get the same performance, but it's better to have the right size.

I don't know if silver soldering will help, but it can't hurt. I know that sweating pipes is a very different soldering exercise than electronics, having done both.
The silver solder is for my wife's jewelry repair! LoL. I have another solder for electrical.
Oh, I understand. It's not the solder, it's the technique, and, frankly, I know little about silver soldering. Plumbing solder must be leadless, and uses one kind of flux and LOTS of heat from gas. Electronics uses leaded solder and a non acidic flux, with surgically applied heat.
""If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you." -- LBJ

Re: Computer motherboard repair soldering

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YankeeTarheel wrote: Sat Apr 17, 2021 5:10 pm
Heretic wrote: Sun Feb 28, 2021 9:24 pm Oh, yes - a simple thing, but easy to overlook...

Don't install the new electrolytic caps backward.

I did this once on a power supply for a tube-type Ham radio transceiver; my cat was not amused by an exploding capacitor, vacating the area at high speed.
Did he leave shit stains on the way out???
He went from "Zen Nap" to "War Emergency Power" in milliseconds, went 3 feet straight up, changed direction 90 degrees in mid-air, launched off the wall through the door, and showed some rather high-G acceleration the instant his paws touched the carpet en route to the other end of the house.

From then on, whenever he smelled the soldering iron heating up, he'd leave the room.

Re: Computer motherboard repair soldering

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Heretic wrote: Sat Apr 17, 2021 9:55 pm
YankeeTarheel wrote: Sat Apr 17, 2021 5:10 pm
Heretic wrote: Sun Feb 28, 2021 9:24 pm Oh, yes - a simple thing, but easy to overlook...

Don't install the new electrolytic caps backward.

I did this once on a power supply for a tube-type Ham radio transceiver; my cat was not amused by an exploding capacitor, vacating the area at high speed.
Did he leave shit stains on the way out???
He went from "Zen Nap" to "War Emergency Power" in milliseconds, went 3 feet straight up, changed direction 90 degrees in mid-air, launched off the wall through the door, and showed some rather high-G acceleration the instant his paws touched the carpet en route to the other end of the house.

From then on, whenever he smelled the soldering iron heating up, he'd leave the room.
:roflmao:

Like Mark Twain's cat who once sat on a hot stove: "He never sat on a hot stove again. Of course, he never sat on a cold one either!"
Sometimes I wonder why we have these useless critters. Then I'll crawl into bed and one (or two) will curl up with me, soft and warm, just wanting to be close, and safe.
""If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you." -- LBJ

Re: Computer motherboard repair soldering

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This is a picture of the blown capacitor. I found an identical old board which I put an offer on.
IMG_3615.JPG
It's the one of the two with the popped cap and orange stuff spilling out. I actually pushed it back, removed the crud and it made an effort to start when I confirmed my diagnosis.
Image
Image

"Resistance is futile. You will be assimilated!" Loquacious of many. Texas Chapter Chief Cat Herder.

Re: Computer motherboard repair soldering

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sikacz, it should be an easy repair, but, I would, if you can, leave the new one with longer leads. It also allows you to heat sink between the soldering point and the cap. Also if something else caused the failure it will be easier to replace it again.
""If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you." -- LBJ

Re: Computer motherboard repair soldering

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YankeeTarheel wrote: Mon Apr 19, 2021 3:22 pm sikacz, it should be an easy repair, but, I would, if you can, leave the new one with longer leads. It also allows you to heat sink between the soldering point and the cap. Also if something else caused the failure it will be easier to replace it again.
Good to know, thanks!
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Image

"Resistance is futile. You will be assimilated!" Loquacious of many. Texas Chapter Chief Cat Herder.

Re: Computer motherboard repair soldering

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He longer leads also bend well. You can solder the new capacitor leaning over to give you space to work and then gently bend it back up straight when done... you know for aesthetics.
"It is better to be violent, if there is violence in our hearts, than to put on the cloak of non-violence to cover impotence. There is hope for a violent man to become non-violent. There is no such hope for the impotent." -Gandhi

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