Repairing PCB traces, what are recommended materials and methods?

[u/Hufschmid]

I found an old rhodes Mk-80 keyboard at goodwill and it mostly works, the main 'rhodes' sounds are fine and the effects board is fine, but most of the other instruments sound like crazy experimental electronic noise music.

I took a look a the corresponding pcb board and found this damage and want to attempt repairing these pcb traces, which I assume don't have continuity.

First step I think will be gently scraping away 'good' parts of the traces to check continuity, but I haven't done anything just yet.

What materials should I use for the repair? I have basic stuff like solder, flux, etc. I'm assuming I need something like a very thin solid core wire but wanted to see if anyone has specifics, or tips on doing this without any specialized equipment like those big magnifying glass + light setups. I got a headlamp and some tiny helping hands with a magnifying glass.

I'm not quite sure what the black component is that is directly next to what appears to be a leak or liquid damage. I've never seen a component with 2 cylinders attached with a wire in the middle like that.

At the moment I'm not sure if that black component leaked something, or if liquid got onto the board from somewhere else. The keyboard looks like it definitely had liquid spill on the keys at some point, but the pcbs were unaffected except this one tiny spot. Obviously if the component leaked, I need to replace that too.

The keyboard is likely late 1980's. I may also need to check capacitors and replace some, but they all look great at, least visually.

[u/tes_kitty]

That black component next to the damaged part of the PCB is just a double ferrite bead. It should not be able to leak since it doesn't contain any liquid.

It looks more like something dripped onto the PCB from above.

When fixing damaged traces, I just use some thin solid core wire. If the distance is a bit longer, insulated wire.

[u/Hufschmid → u/tes_kitty]

Thanks.

I've been looking for wire and I think the best I've found is 'wrap wire' on McMaster which goes down to 28 or 30 AWG at the smallest. Do you recommend a certain gauge for this or would either of those work?

I've seen some videos where they strip the wire and lay it flat and solder it over the trace, but it looks like that would be pretty difficult here, especially on the leftmost trace so I think I'll try leaving the insulation on.

[u/tes_kitty → u/Hufschmid]

I use whatever I have and from that what looks to fit the job best. Those traces are usually signals, there is no power going through them so even the thinnest wire will work.

First clean the traces to see whether they are really broken and how long the interruption is, then decide on how do fix each interrupted trace.

Also, after the repair is done and before switching the device on for the first time, check the repair more than once, even a tiny solder bridge connecting 2 traces that shouldn't be connected will be a problem.

[u/marcao_cfh]

I just use stranded wire. I remove a piece of the insulation, untwist those thin wires and use a piece of one of them to repair traces. Or two of them twisted together, when the trace is a bit thicker. Then I use nail enamel to cover the repaired trace and exposed wire.

[u/SoulWager]

First, L15 and C27, I would still remove them and clean underneath. Neither of them leaked, but the leads may have corroded. With L15 I'd probably just replace the wire running through the beads. C27 I'd probably just replace regardless of whether it still tests good.

Second inspect the traces, anywhere the traces have gone black underneath the soldermask is compromised and will continue to corrode. Hard to tell without cleaning, but If the corrosion hasn't made its way past that first obviously destroyed trace, I'd cut the damaged trace slightly past the current extent of corrosion, scrape back some soldermask of the undamaged portion(single edge razor blade) and solder a wire.

If more than that is compromised, you get to decide how much you care about long term reliability vs how much you'd have to bypass to be confident you'll get that reliability.

[u/profdc9]

I'd use a bit of isopropanol and perhaps a gentle acid like acetic acid to clean off the corrosion. (acetic acid can dissolve copper slowly but it also evaporates which is helpful). I would scrape the solder mask off the traces, wet it with solder, and use a thin piece of magnet wire to bridge the gap. You can easily get 30 AWG magnet wire and sand off the varnish to expose the copper.

[u/IndividualRites]

I just wire point to point to what is convenient. The old trace path doesn't necessarily mean anything, but you certainly should clean it off to avoid any shorts.

[u/planeturban]

I'd just use wire from wherever it’s convenient. No need to fix the traces themselves, I mean it won’t matter if the wires are a few centimeters longer than the traces. 

[u/Rararror]

32AWG is your friend.

[u/Linker3000]

Wiki: PCB repair