Replacing potting material - washing machine controller PCB repair

[RobertHolcombe]

Hey,

I have a Simpson washing machine that has touch-sensitive buttons for selecting wash settings, as well as the start/pause button. The start/pause button has become intermittent and sometimes the machine pauses itself in the middle of a cycle. I pulled it apart and found one of the two 400V 4.7uF mains filter caps was bulging, it reads 3.6uF and nothing on my ESR meter, the healthy looking cap measured in spec and around 6.5 ohms ESR. I replaced both caps and am going to test it tonight.

As per the title, I'm curious what people would use as a replacement potting/encapsulation material. The original material is soft and was actually quite easy to remove, the consistency is like that of gummi candy. It didn't seem to have bonded all that well to the board or components like most silicone I have used, I removed it easily with a greenwood stick. Ideally I'd like to use something similar just in case I do have to rework it again, rather than something more permanent.

Does anyone have any suggestions?

[tautech]

The thick conformal coating is only there to protect the PCB from the sauna like climate in a washing machine so most anything that provides protection against water vapor and provides insulation should do.
What about good old candle wax on just your rework area.

Or Jaycar PCB lacquer.....CAT NA-1002

[xavier60]

Hey,

I have a Simpson washing machine that has touch-sensitive buttons for selecting wash settings, as well as the start/pause button. The start/pause button has become intermittent and sometimes the machine pauses itself in the middle of a cycle. I pulled it apart and found one of the two 400V 4.7uF mains filter caps was bulging, it reads 3.6uF and nothing on my ESR meter, the healthy looking cap measured in spec and around 6.5 ohms ESR. I replaced both caps and am going to test it tonight.

As per the title, I'm curious what people would use as a replacement potting/encapsulation material. The original material is soft and was actually quite easy to remove, the consistency is like that of gummi candy. It didn't seem to have bonded all that well to the board or components like most silicone I have used, I removed it easily with a greenwood stick. Ideally I'd like to use something similar just in case I do have to rework it again, rather than something more permanent.

Does anyone have any suggestions?

Flowable neutral cure silicone is my first choice but too expensive for a one off repair.
Just about any neutral cure silicone or MS sealant should do. Let us know what you have handy.
Beware of fake LNK306 from ebay.

https://www.amazon.com.au/Permatex-81730-Flowable-Silicone-Windshield/dp/B000BKEBO0/ref=asc_df_B000BKEBO0/?tag=googleshopdsk-22&linkCode=df0&hvadid=341743346373&hvpos=&hvnetw=g&hvrand=7845969249577986718&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9068976&hvtargid=pla-406644581015&psc=1

[BillyD]

The thick conformal coating is only there to protect the PCB from the sauna like climate in a washing machine so most anything that provides protection against water vapor and provides insulation should do.
What about good old candle wax on just your rework area.

Or Jaycar PCB lacquer.....CAT NA-1002

Interesting, hadn't heard of using candle wax like this before. Is it much good? I can imagine it might start cracking and flaking if there's much movement or vibration.

[RobertHolcombe]

The only thing I have on hand is permatex ultra grey and ultra black, if I were to use silicone I'd want it to be clear, but I think I'll go with spray lacquer anyway, I like the idea of a thin coating

The start/pause button seems to be working as normal now so I'm hopeful its a permanent fix, its in the middle of a cycle now and I haven't heard it stop yet 

Thanks lads

[pbarton]

Search for, "Crocell hot dip strippable coating"
Typically used on machine tools, to stop them rusting.
Designed to keep moisture out.

[tautech]

The only thing I have on hand is permatex ultra grey and ultra black, if I were to use silicone I'd want it to be clear, but I think I'll go with spray lacquer anyway, I like the idea of a thin coating

The start/pause button seems to be working as normal now so I'm hopeful its a permanent fix, its in the middle of a cycle now and I haven't heard it stop yet 

Thanks lads

I use the Jaycar lacquer on many repairs where moisture might be an issue and for general PCB protection in NZ's damp climate. That you can also solder through it is immensely useful. 
If I etch a PCB and not to use it straight away, it gets a light squirt for protection then goes into a ziploc bag where I know it will stay perfect for years.

There are many similar ones available from the big suppliers however in Oz or NZ and if you have a Jaycar shop close by it's pretty convenient stuff to have near the bench.

[cozza]

https://www.jaycar.co.nz/liquid-electrical-tape-tube-black/p/NM2836

This sets up like latex and you can peel it off to remove it, unlike neutral cure silicone.

It is solvent based, you may want to check compatibility with the components underneath.

It'd be good for providing some mechanical strength to the electrolytic caps, there's a lot of vibration in a washing machine.