I have to replace two capacitors in an automotive circuit board. The board is for the ADS (Adaptive Damping System) for a 1999 Mercedes SL600. The board is shown below with the two caps circled. For reference these are 220uF 25V capacitors. The problem I am having is the board is covered with some kind of thick varnish on both sides. The varnish seems to be acting as an insulator and I cant get the solder to melt. I believe I need to clean that off in the area of the caps. Dose anyone know what that coating might be and what is the best way to remove it in the area of the capacitors?. I am using a Hakko FX888D soldering station, They are fairly heavy caps but I think it should handle it.

 

Its a 'conformal coating' intended to prevent moisture attacking the board. My experience is that mechanical removal is the only effective way allow desoldering and maintenance.

 

Maybe you could cut the leads and solder the replacement capacitors to the remaining leads. You should probably fix the new caps to the board with silicone for mechanical support.

 

these things are in a terrible environment for electronics .
electronics hate hot, cold and moisture , all of which car parts are susceptible too.

as per @boostbuck , thats a conformal coating , sprayed or dipped onto the board.

standard old school solvents such as iPa might clean it

companies such as rs components used to, I've not checked recently, sell sprays of conformal coating and removers.

but , a quarter century ago, these things were a little less common, and the thing could have been dipped in yatch varnish !

Just a word on safety.
if this part fails in operation, is it safety critical, what happens to the car then? if the cars doing 90 , overtaking and the damping goes wrong , either over or under effect, what happens ?
if you prepare this , its operation is on your insurance / head.

cutting the capacitors off, and using the existing leads is possible way forward. but be aware as mentioned , that is not mechanical robust , so they will need extra support,

your probably going to have to scrape the leads you cut to get a good connection,

remember to clean the board very well, and re apply conformal

 

Thanks for all the quick replies. A assume iPa is Isoproply Alcohol. I have that as well as Acetone available. This company offers conformal coatings. Look like pretty expensive stuff at about $45 a spray can. They also offer a conformal coating stripper at about $90 a gallon. Hope the alcohol works. I noticed acrylic bases coatings show a picture of a car, There silicone based show a picture of a helicopter.

https://miller-stephenson.com/chemi...dG2n4kgr-WGaVkCOMB3zon9sBBC9YIyAaAoQMEALw_wcB

Digikey offers a conformal coating cleaner and remover at a more reasonable price.

https://www.digikey.com/en/products...MYHsB2AzBAnAtgQwDYAJFsAXASyQHNDcBTbJG9EAXQF8g

https://www.digikey.com/en/products...EkuXhD-MNGlAdo_5X9qqRCsLuEmo1ZRsaAj8iEALw_wcB

As far as safety is concerned. Typical failures of this system will not allow the car to raise or lower in accordance with programed speed or user commands. In the event of a worst case hard over situation (which I never heard of) the car would either rise or fall to max or min height but it would do so only as fast as the pump will allow, which is about 30 second from low to high, possibly on one axle only. It also might make the car run with more or less damping. Nothing remotely comparable to a flat tire.

Good information on these conformal coatings. I should probably use them on my other circuit boards. Most recently I completed a fan controller.

 

Why are you replacing them?

 

Why are you replacing them?

Its a known failure mode, especially on 25+ year old electrolytic caps. I did some limited testing with them installed. Not sure what its worth testing them installed but the fact they are both different results for similar circuits is a clue. Might explain why the front responds but the back does not.

Cap #1 7uF ESR 1.1Ω Vloss 8.8%
Cap #2 135uf ESR 1.3Ω Vloss 7%

 

Good luck.

 

Clip the leads close to the capacitor body, then use the leads to connect the new caps.

Removing the conformal coating will compromise the environmental protection of the board.

 

Success today. Caps are in and tested. I found IPA would not do anything to this coating. I have no idea what it is but it seams like a Bosch proprietary ceramic coating. So what I did was just scrape away the end of the protruding lead with a razor blade until base metal was exposed. Once that base metal was exposed I could just press down on the protruding lead with a chisel tip tinned soldering iron until it was flush with the board. Then I could use my needle tip to push it right through. I cleaned up the holes with a 1.5mm drill bit using my fingers and cleaned the pads with a 3mm drill bit.

Now I can just apply some conformal coating with a brush at the solder pads.

Thank You for everyone help.

 

thanks for getting back , been wondering how it went.