Cleaning products for use on old PCBs

[jamesmafyew]

I've got an Ampeg V4B on the bench that was "eating tubes". Turned out, there was solder crust/flux/whatever on the PCB causing leakage between one of the screen resistor pads and one of the grid stopper pads, pulling up the -DC bias on one of the power tubes. The PCB in this thing is a mess, all sorts of black stuff, dirt, solder flux, etc. Can't tell if it might have had a fire in it, it's so nasty. Seems to work though, now that I removed the crud from between those two PCB pads.

What kind of product would be safe for me to use to clean this thing? IPA? Blue Shower? I don't want to ruin the PCB, but the dirt in here seems to me to be a serious reliability problem.

[J M Fahey]

To clean rosin(flux) related stuff, use a toothbrush and some kind of alcohol.
Soak>brush>absorb with clean cotton balls or tissue paper, then repeat.
For harder to remove stuff, soak in more alcohol , cover with a plastic trash bag simply so solvent does not evaporate so quickly and let it rest for 1/2 hour, then repeat cleaning.
For carbonized residue, use a hard nylon or bristle brush in your Dremel.
*Only* if you have a very old board with exposed copper (no solder mask) which has turned green or something, use *lightly* a brass bristle brush in your Dremel until copper is shiny and solder is dull, then paint visible copper and solder with 1 ounce rosin in 4 ounces alcohol flux.
They will be protected and easy to solder.
Do everything with good ventilation, use a mask if cleaning green copper salts, which are very nasty.
I have reclaimed old PCBs in pityful state.
Worst enemy is dampness.

[jamesmafyew]

Thanks, very helpful.

One other thing: any issues with carbon comp resistors soaking up the alcohol? I've heard they're pretty susceptible to moisture penetration.

[J M Fahey]

Thanks, very helpful.

One other thing: any issues with carbon comp resistors soaking up the alcohol? I've heard they're pretty susceptible to moisture penetration.

Maybe, but alcohol evaporates easily and in full, and in the process carries moisture away so in fact it will dehydrate your resistors.
After cleaning I would leave the amp in the Sun a couple hours to be certain, or in Winter, blow some hot dry air towards it.

[olddawg]

Denatured alcohol for sure. Do not use rubbing alcohol with a high water content. A blow dryer helps but be careful, alcohol is very flammable. I used to use a sonic cleaning bath in the shop. Made boards look like new. You can fake one with a driver, a metal tray, an amp, and a signal generator. But you have to remove the board of course, which may be cost prohibitive.