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I have rescued many retro computers from the hazards of leaky batteries, and occasionally replaced capacitors that were suspicious. Except for one still unusable Mac SE/30, all my repairs were done before the leakage created any serious damage to the traces on the motherboard.

After supporting this project to recreate the Amiga 4000 motherboard schematics and build files, I got to thinking about what other options are available for amateurs trying to repair damaged motherboards like the A4000 or my SE/30. The typical damage I'm aware of would be one of these:

  • Corrosion of traces from a leaky battery or capacitor.
  • Corrosion of traces from really bad storage conditions.
  • Lifted solder pads from attempted repairs (probably re-capping) gone bad.

There are probably other cases that an experienced tech could add to my list. For these types of repairs, what are the best ways to proceed in making a reliable repair? Also how do you know when a board is "beyond repair"?

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Restoring to an as-new look is likely not possible with the damage described. Most western PCBs used for computers use solder mask (the green stuff) over the traces - if corrosion happened UNDER the solder mask, you would probably need to remove all the solder mask before treating the traces itself. Solder mask is available as a canned product for manual application from some suppliers, it is however questionable whether an original look can be restored.

If any destructive corrosion has happened to inner layer traces in a multilayer board, it is unlikely you can do anything but replace the trace with a wire.

Once a trace is bare and clean, you could improve it by tinning it (or even soldering down a wire parallel to it). Or, you could use some chemical plating (galvanics kits) method, however, you would need to apply voltage to some spot on the trace and work very precisely so as not to cause electrical damage to anything; Also, not every plating keeps well on every metal. Unless you want to work with actual electroless plating solutions, which - even if somebody is willing to sell them to you - are sometimes extremely toxic compounds (there is raw cyanide in substantial amounts in some).

You best bet to deal with traces that are actually gone is using magnet wire, or small coaxial cables for really sensitive stuff (they can be salvaged from surplus VGA cables and the antennas in scrap laptops). If you need a stable pad to solder something to, cut out a small square of unetched PCB stock or even copper foil, roughen both the back of it and superglue it to an also roughened place on the PCB (where no traces are). Double check the mechanical stability after soldering to it, some super glues do not suffer soldering heat well. To hold things mechanically stable, kapton self-adhesive tape is a good option.

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    Am I correct in assuming not having any schematic is a serious setback? Or is decent magnification enough to sort out what went where before the damage? – Brian H Apr 12 '18 at 23:46
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    @BrianH It is. Sometimes PCB traces are so badly damaged that it is impossible to trace from the remnants what originally went where. – tofro Apr 13 '18 at 7:25
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    Component datasheets can help there too: Address lines tend to go to address pins, clocky stuff tends to go to clock inputs, etc... – rackandboneman Apr 13 '18 at 7:47

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