Evening all,

I just got done with my first time using circuit board epoxy and I’m really stoked how it all turned out. Not perfect, but damn close!

For starters, I bought some flame retardant circuit board epoxy because I wanted a more modern and safer choice to the old tar from 49yrs ago. Nothing like an accelerant hanging just above your fuel rail in the event of a fire am I right?!

Here’s the product I chose:
https://www.amazon.com/MG-Chemicals-Black-R...d/dp/B07B3Z8CLY

Regarding the removal of the tar, there’s no way around it, it is a tedious task. My method of choice was to use a box knife to slice up the tar and then used a flat screw driver to remove the bulk until I got down to the base. From there I took a full assortment of tiny screw drivers and used an appropriate size to clear the channels where the copper strips run… like a tar shovel. Then at each wedge location, I use a pick to clear out those areas. An air hose is handy to blow away the shavings as you work.

Once I hit the limit of productivity there, I took some citrus based bug and tar remover as well as a wire brush to remove the stuck on bits. This step again is tedious because you have to rinse with soap and water to check your progress before reapplying more citrus remover and going again.

When the tar was gone, I then took my favorite phosphoric acid based rust remover to deoxidize the copper strips. I had some corrosion even under bits that were still covered in tar. After a very thorough soap and water rinse to remove the acid gel. I went after it with an air hose to dry it off and bake it in the oven for an hour on the lowest setting (170F for mine).

After it cools, it’s time to start sealing the holes. I used high temp gasket maker. With a small tip, you need to fill the holes:
-where the voltage regulator connects
-where the alternator connects
-where the cable hold down clips (used to go)
-where the two tabs are on the end
-where the VR screws go… actually it’s best to install the screws so you can get molded thread holes

Be sure to get that RTV all the way up in there! This was my one mistake, but it was recoverable thankfully.

For the air channel under the voltage regulator, use a polymer eraser cut to fit and jam it in there till it’s flush with the top side.

Now it’s time to set up for the pour.

As you can see above, I used a box as a pour platform and catch basin if I had spillage.
You need to perfectly level your platform regardless of what you set it on.

Follow the instructions on the epoxy and if you can, degas the mix before pouring. My board surprised me by taking the entire 375ml of epoxy.

I tried to tap on it as much as I could without disturbing it so I could free the trapped air under the strips, but that was a challenging task. I also let it sit periodically so they could rise naturally. In the end I wasn’t able to get them all, but I got the vast majority.

After I let the epoxy sit for an hour at room temp, it was off to the oven for baking. This epoxy wanted 1hr at 175F.

My rig here was pretty fancy as you can see

After an hour she was fully cured with only a couple bubbles that didn’t catch the train. None of them too deep though.

This is the point where the polymer eraser makes it’s money. When the part is cool enough to touch, you can pry the eraser out and it only leaves a thin skin of eraser behind.

And with that, I now have a freshly epoxied, flame retardant relay board that will outlive me!

hope you are not going to bake cakes in that oven for a week or two!

nice work.
better unbolt mine and see how bad it is.

Lol… it will be spending the morning in self cleaning mode. But the temp is so low that this is not even the same category as baking off powder coating. Very low fumes by comparison.

Huzzah! Awesome job, pal.

Nice write up!

Thanks guys. Since I'd never done anything like this before, I was apprehensive. But once I got it all mapped out and understood the objectives and requirements, I got my confidence back.
When it was all done, I was so pleased with how smoothly it went I thought it was worth sharing.
Further, I think it's a reasonable statement when I say that everyone of us needs to do this to our 50yr old relay boards!

nicely done sir!

Great.

Now I have another project

Nice job