Circuit board repair?

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CalebJ

CalebJ

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I picked up a '94 Camry as a beater car for work miles last week. Mechanically it's pretty solid, but I did discover some quirky transmission and electronics issues that quickly lead down a rabbit trail that ended with blown capacitors on the computer (see thumbnails below). I've done some soldering as needed in the past, but it's generally to put things together rather than take them apart... I found suggestions to clip the caps off and scrub the affected areas with isopropyl alcohol and rinse with distilled water. That's done, but now I'm struggling with removing the remaining bits of solder to clear the through holes for installing the replacement caps. Heating it with an iron and using a cheap desoldering pump didn't do much, and a bit of solder wick didn't seem to do much either.

If anybody has experience in this area, I'd love to hear feedback. I don't have any solder flux, but just ordered a bit on Amazon that should be here on Sunday.

Thanks for whatever advice you have to offer!

1637345608478.jpegC115, C120 failure.jpg
 
Solder, flux, and a solder sucker....and maybe some solder wick....and a whole lot of patients. Do not over heat the board or you'll lift runs and burn out eyelets.. We do this sort of thing at work all the time, and sometimes the only thing that works is putting solder BACK into the affected spot enough to wet/melt the stubborn bits....and suck or wick it out.

But never, ever do any of that without flux to aid in heat transfer and keep from oxidizing the rest of it.
 
Thanks! Is the flux I'd need for this available off the shelf at typical local stores? I didn't know exactly what I was looking for so I wandered around Amazon for something specifically indicating electronics use. But if I can grab it this evening and cancel that order it would be preferable.
 
Solder wick and a flux pen. Use the flux pen on the solder wick and then use that on the spots you want to desolder on the board. The wick will suck up the melted solder and leave clean, tinned pads. Some of the newer lead-free solders don't reflow well so you can add just a touch of leaded solder to them before trying to desolder them to help it melt at a lower temp and cleanly.
 
Pretty much any electrical flux. It's non-corrosive. Should be available from any electronics supply place locally, if you have one (my locality is 1.8M people, 1 electronics supply place.....and it closed this year). I had to resort to Hobby Town once in a pinch earlier this year, their Radio Shack line had a small tub for cheap and it's served well.
 
I whacked a trace on an EggTimer GPS board way in the past. I messed it up during soldering and did a "wire" bridge. Still works to this day actually. Kurt Savegnago
 
A kit should be good if it's from a reputable source.

Looking up the mfr/series at Mouser, DigiKey etc will help you identify what they're intended for, and have data sheets if you want to check.
 
This is what came in the kit (multiples of each, but these are all the types):
1637354770093.png1637354802086.png

I'll see what sort of info I can scrounge up on them. Looks like the blue ones are jb, the 15 and 47 uF black ones are Kemet, and the 100 and 220 uF black ones are Chenxing. Thanks for the tip.
 
Any names/numbers and the vent pattern on top will help you ID them.

Clip from a post in the Club Lexus Forum made by a Toyota ECU engineer (Yamae) from the 90's:

"Those who want to replace Nichicon's type PF(M) capacitors to avoid future problems, be sure to use low ESR type capacitors. Never select capacitors just seeing the voltage and the capacitance. I recommend you to use Rubycon's type ZLH or Nippon Chemicon's type KZH. These do not contain infamous "quaternary ammonium compounds" but their ESR is low enough. You also have to pay good attentions against electric static discharge when doing the replacing job. A wrist strap is definitely needed to use. Without it you might damage the ECU. "

The first post in this thread has some good information about the issues and links to replacement caps. Yamae's first reply is in post #8:

https://www.clublexus.com/forums/ls...ved-ecu-leaking-capacitor.html?ispreloading=1
 
That thread is a great source. I was going to use it to order replacement caps based on their recommendations, but even with multiple suggested part numbers there are some totally unavailable. I may go ahead and use what I've got for today and stick a reminder in my calendar to check again in a couple of months to see if I can get a complete set.
 
Are you holding the circuit board in some sort of fixture? You can heat the solder pad from one side, and try to push a needle or other sharp, thin probe through from the other side. When the solder is melted, you should be able to push the small piece of capacitor lead out of the circuit board. Next time, don't cut the part off so close to the board, leave some wire sticking out to grab onto.
 
There's a tiny bit to grab. The caps were installed very close to the board so i couldn't leave much more there (at least with any tools in my collection).
 
CalebJ said:
There's a tiny bit to grab. The caps were installed very close to the board so i couldn't leave much more there (at least with any tools in my collection).
Click to expand...

Might require two steps: heat and melt solder - push bit of wire through circuit board with a needle, then flip circuit board, heat again to melt solder and pull wire out. I've had problems like this, too. Sometimes you can suck the errant bit out, sometimes you can *blow* it out (when solder is melted). Another tip - you've already determined the component is bad, it won't get any worse. I'd cut the cap apart with some heavy wire cutters, leaving the wires below the component intact. NOW you have something to grab onto!

Also - good desoldering pumps aren't very expensive. You want a piston-type pump, not a bulb-type. Sometimes you *really* need a good quality single-purpose tool.
 
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If the caps have been clipped out and you have short lengths of lead remaining in the holes, I would hold the board in a clamp so that it is vertical. Apply flux from a flux pen to both sides of the board over each hole.

Using a primed piston solder sucker held onto one side of the hole, heat the solder and lead wire from the other side. When the solder melts, trigger the solder sucker to remove the lead.

Don’t waste too much time with the iron otherwise you’ll damage the pads. The flux aids in distribution of the heat as it boils. You need to use the sucker while the solder is fluid, not while it’s already cooling.

If you’ve used sharp wire cutters, then the lead will have a clean cut that hopefully won’t jam in the hole. If the lead has been bent when installed, then you will have to be more careful.

Better still, use a proper desoldering station!
 
Often board damage happens because a person uses too small of a tip or not enough heat and has to linger a long time. Heat transfer takes time. You want to melt the solder quickly so you can get done quickly before the board is damaged. I definitely agree that it’s key to cut through-hole component leads close to the component so you have something to grab to pull the lead out. Lots of flux (not all fluxes are compatible even within a subgroup) but “Radio-TV solder” or rosin core solder (and separate rosin flux) is usually appropriate for older through-hole boards.

I’ve gleaned from Cris Erving’s eggcellent instructions not to use rosin flux or solder for surface mount boards because it’s possibly not compatible with the no-clean 247 or 291 solders and associated fluxes.
 
heada said:
Solder wick and a flux pen. Use the flux pen on the solder wick and then use that on the spots you want to desolder on the board. The wick will suck up the melted solder and leave clean, tinned pads. Some of the newer lead-free solders don't reflow well so you can add just a touch of leaded solder to them before trying to desolder them to help it melt at a lower temp and cleanly.
Click to expand...
One small warning: Absotively, posilutely do not use plumber's soldering flux. It is highly acidic and will very likely result in the eventual failure of the board!!!

I would go further on the subject of solder - if at all possible, try to find some leaded solder. Although I have no personal experience with the lead-free (ROHS compliant) solders, I have heard of a lot of difficulty with them on electronics...
 
Sooner Boomer said:
Also - good desoldering pumps aren't very expensive. You want a piston-type pump, not a bulb-type. Sometimes you *really* need a good quality single-purpose tool.
Click to expand...
EDSYN DS017 The Original Deluxe Solder Sucker SOLDAPULLT https://www.amazon.com/dp/B006GOKVKI/ref=cm_sw_r_cp_api_glt_fabc_AFV5NG65KDHTESHXCDM6

I’d recommend one of these. Back when I was the QA/repair guy at a guitar pedal company (and removing and replacing components on everything all day) I went through a few of the cheaper ones, and while they typically worked well enough, they’d all clog frequently and eventually fail. The few others I tried didn’t have the same suction of the Edsyn ones. I’ve probably sucked up about a pound of solder through the one I’ve got now.:)
 
Thanks - I added that one to my cart. Looks like the flux I ordered was just delivered. If I can't finish the project this afternoon with what I've got, I'll get that ordered.
 
KC3KNM said:
EDSYN DS017 The Original Deluxe Solder Sucker SOLDAPULLT https://www.amazon.com/dp/B006GOKVKI/ref=cm_sw_r_cp_api_glt_fabc_AFV5NG65KDHTESHXCDM6

I’d recommend one of these. Back when I was the QA/repair guy at a guitar pedal company (and removing and replacing components on everything all day) I went through a few of the cheaper ones, and while they typically worked well enough, they’d all clog frequently and eventually fail. The few others I tried didn’t have the same suction of the Edsyn ones. I’ve probably sucked up about a pound of solder through the one I’ve got now.:)
Click to expand...
I also highly recommend this type of sucker. I still have one that I was given back in the late '70s and it gets used regularly. Plenty of volume which helps clearing the holes. Don't buy the smaller ones as they don't have the volume and can be more damaging to the PCB when used. Air volume is important as it sucks the solder out but also cools the legs and stops them binding to the sides of the pad hole barrel. Adding solder to the hole (helps heat conduction) as mentioned upthread is useful, and cutting the legs flush with the top of the board can help too, but don't discount the utility of having a bit of wire poking out to grab onto too early ;).

FYI if the board has internal power and ground planes they suck the heat away and make removal of parts difficult. If you preheat the board to about 120degC in the general area around the part to be extracted then the part removal is much more successful (heat flow away from the pin is reduced). We have backheaters specifically for this purpose and they work wonderfully. You might be able to carefully use a hair dryer or hot air gun to assist. Be very cautious if using a hot air gun and don't get too close or too hot.
 

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