Dealing with battery damage

Any pointers/advice on dealing with PCB battery damage on a synth PCB? I get cleaning it up and testing the parts around it. What I would like more substance on is neutralizing the acid and repairing traces.


This sort of repair is very tedious - which makes it all the more rewarding when you finally bring it back to life!

I’ve done this on several Korg Polysix boards, and here is the procedure.

(1) Remove the old, leaky battery, of course. And at this point, you might want to consider changing the type of battery. On the Polysix, for instance, the original rechargeable NiCad battery is leak-prone when sitting unused for a long time. We sell a kit to change this to a non-rechargeable Lithium ion battery, which will not leak. But you CANNOT change from a rechargeable battery to a non-rechargeable one without changing the circuit (hence the kit).

(2) Wash the circuit board as thoroughly as possible. Unless there are moving parts, like switches, pots or trim pots, I just put the entire circuit board in a sink of warm water and dish soap, and go after it with an old toothbrush. Then let it dry. People often think that electronics + water don’t mix; it’s actually electricity + water that is a bad combo. Most circuit boards don’t care if they get wet (again, it’s just things with moving parts that you don’t want to get water into).

(3) Now it’s time to examine the board very closely and start repairing. You will want to have a multimeter with a ‘beeper’, a strong magnifier and an X-acto knife. You will also want to have a print-out of the board layout, showing a picture of the PCB traces (most service manuals have this). The plan of action is to test every single trace on the board in the affected area, and repair as you go. You can see what an unaffected trace looks like - it’s a shiny copper path, usually with a layer of greenish varnish over it. You can also probably see that the affected traces have turned black underneath the varnish - they look blotchy and corroded. Find two solder points along a single clean trace, and you should be able to beep between them (by placing a lead from your meter on each solder point). When you do the same thing on a corroded path, you may or may not get a beep. Beep = electrical continuity.

(4) On a corroded path, whether it beeps or not, you will want to scrape off the varnish coating with the knife, then continue scraping to remove any corrosion, leaving just shiny copper. The reason you are doing this, even on traces that test ok, is that the corrosion will continue to spread unless it is removed. And this is a good time to say that I have even seen that corrosion travel through wired connections to an adjacent circuit board!

(5) Once your trace is free of corrosion, test it again with the meter. If you still get a beep, you should be okay to leave it as is. If it looks like there is barely a copper path left, though, you might want to repair it, by soldering a thin wire bridge over the damaged area. You can use a piece of insulated PCB repair wire, or you can use a strand from a piece of braided wire. In any case, you won’t be able to solder to the PCB trace unless it has been scraped clean. And if you are using bare wire, keep the wire flat against the trace so that it can’t touch anything else.

(6) After testing each trace, and repairing when necessary, ‘trace’ that trace with a colored highlighter on the printed PCB layout to show that it is good.

(7) Continue in this fashion until all traces in the affected area are colored.

Some things to remember: You may need to replace components as well, such as ICs that have corrosion leading up to them. Also, you are probably working with a double-sided circuit board, so you need to do this procedure for each side of the board. If a trace moves from one side of the circuit board to the other, test with your meter to make sure that you have continuity at the hole where it passes through. And once you are finished, if the keyboard acts strangely, you have probably missed a bit that needs repairing (or perhaps you have shorted two traces together).

This is likely to be a long and tedious project - but it’s a great feeling when you’ve brought your synthesizer back to life! Good luck!

1 Like

OMG!! That is a FANTASTIC explanation!!! Thank you so much! It seems straight-forward but having somebody with your knowledge to give some pointers is extremely helpful.

A couple of other questions…I’ve seen some references to neutralizing the leakage. I’m a bit confused with this. I would think that the leakage is an acid, so it would need to be neutralized with some sort of base. But then I’ve seen reference to the leakage being a base and needs to be neutralized with an acid (vinegar). Any comment on this?

I also bought an ultrasonic cleaner (not the jewelry kind…better) with the expectation of cleaning circuit boards. It is big enough to fit a decent sized board and it has both the Degas and the alternating frequency feature. As long as there are no sliders, pots, tuners on a board, should that be a good option for cleaning?

Thank you so much for your time and help! I LOVE this forum!!!

Add this to cleaning battery acid off PC bds to your list, my first cleaning procedure is to apply baking soda and white vinegar to the affected area which should neutralize any acid residue. Then I proceed to a good strong detergent [I use Greased Lightning] a thorough rinsing and into an oven @ 200* for an hour. The board is now ready to troubleshoot trace quality and any residue should come off very easily.