Electronics > Manufacturing & Assembly

Probing old, corroded, conformal coated units when fault finding?


I had to probe nodes on a 4kW PSU while fault finding. The conformal coating seemed to have got on the soldered thru hole pins so it was hard to probe them. Also the unit had been in use for years and so the exposed metal pins and pads were kind  of a bit corroded.
Eg a fuse was good, but I couldn’t get contact whilst probing between its metal holders.

I tried to probe the primary rail. The only way I could do this was to melt solder up on the pins of the bus capacitor…...and  only then I could sucessfully probe it.

How can you fault find boards like this? Do you literally have to just go round the pins with a hot soldering iron and re-wet the solder joints? Kind of melting off the conformal coat and busting through the corrosion. You cant seem to find those sharp-point probes anywhere.

I have soldered sewing needles to .080" pin jacks that fit over the ends of the voltmeter probes.  The needle points make good contact through wire insulation, most conformal coatings and corrosion.  Getting the solder to wet to the needles is tricky.


Sharp point probes are commonly available:


I once ran into this issue. Finally ended up cleaning up the coating using IPA and a brush.


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