Fixing pcb boards with epoxied connections

I was going to reply to myself in 'life goes on" but I will never find the post again, and the information might be useful to others maybe with expoxied boards on generators. It is fairly common to have a resin applied to boards for waterproofing. Capacitors do go bad.


This is from a zoro actuator valve which is common in heat pumps and other water control applications. the part itself is like 110 dollars or 130 with the actual valve.

In this picture you see the two tall tank(cans) capacitors, the one on the left is clearly bulging, and the one on the right doesn’t look quite even. about 90% of the time, a cap will bulge when it goes bad, and if one fails, the next one especially from the same batch will have a similar failure shortly. The board is clearly epoxied in and the epoxy appears to be holding the board in the case.

Before doing -anything- it is an electrolytic capacitor there is a positive and negative lead so document what side is what before doing anything. Even if you can see the markings on the board, they may be wrong. In this case there is just a stripe down the side of the capacitor. And also note the voltage and capacitance of the capacitor which is marked on the side of it. So you can find a replacement. It can be a higher voltage, but not a lower voltage, and for capacitance there is some wiggle room, but get as close as you can typically err on the side of larger.

There are several strategies you can take.
The first is the easiest,
-Cut the tops off of the caps and remove the ‘can’ portion you just cut off. Note the value & polarity. Remove all the layers of dielectric etc from the center of the caps until you can access the two leads in the bottom of each can and solder to the leads. Attach your new capacitors to your newly soldered leads and secure the newly installed capacitors in a safe place within the housing with hot glue, silicone etc.
It won’t be pretty, but it does work! —alternatively-- you don’t actually need the leads, you can just use the new capacitor wires, but it gets tight trying to solder.

-Chemicals typically don’t work. If the chemicals works, they can also eat through the board and components on the board. They work slow and can be very harsh. Apparently you can also apply the chemical to soften the layer and scrape away at it a little bit at a time.

-The last viable option is a heat gun, dremel and other hand tools like a knife, dentist pick, etc. to very carefully, sand, grind or chip away at the epoxy layer. There is a commercial product called Pace LapFlo Handpiece that will sometimes work. :slight_smile:

Sometimes heat can loosen it a bit to make it easier to pry, but not too hot.

-then there is this:
Epoxy resin will usually soften in boiling water, then you can pick away at it with a screwdriver although the relay there won’t like the water! If you can warm up the PCB in an oven to about 120C, then use soldering iron set to about 130C, you can use it as a chisel. Whether or not the PCB will be reusable is a different story, but this approach works for reverse engineering!