Removing Potting

[Andy1845c]

Has anyone ever had any luck de-potting a circuit? I bought 5 strobe light power supplys in need of repair off ebay. Of the 5, the three that were not pictured are fricken potted!

Will it re-melt at a temp that won't melt the rest of the circuit?

 

[Nigel Goodwin]

Potting is usually either epoxy resin or silicon rubber, I don't think you can melt either of those?. Depending on the material you 'may' be able to use a solvent - but it's likely to be very difficult to source?.

However, it's certainly a dishonest sale to sell potted ones and not tell you!.

 

[blueroomelectronics]

A heat shrink type blowdryer will soften it up, then just peel away.

 

[Nigel Goodwin]

A heat shrink type blowdryer will soften it up, then just peel away.

Epoxy resin?.

He hasn't actually mentioned the type of potting, but most I ever see are epoxy.

 

[Andy1845c]

I don't really know what type of potting it is Its green and I can poke into it a little with a screwdriver, so its not super hard.

 

[Stellarcore]

The stuff we use at my work is really difficult to remove. It is really neat stuff.

It hardens by some chemical reaction that generates heat, heat also makes the reaction go faster. The end result is that the larger the volume of potting material you're using the faster it hardens.

The only way I've seen it removed for debugging purposes around here is to physically (and very carefully) cut it out with a dremel or sharp knife.

 

[HarveyH42]

I removed some green stuff a few weeks ago. It was kind of gelatinous, messy stuff. Cut and scoop out as much as I could with a knife and a spoon, until the board came free. Took it outside and used a light wire brush to get most of it clean, a little acetone on the solder side. One power lead was broken off, easy fix.

 

[Shax]

If you have a pcb with the soft silicone based potting compound, then take a quick trip to the local diy store to pick up some silicone sealant remover.. Works for me every time..

Don't be tempted to use standard acetoxy silicone for repotting. The Acetic Acid given off during curing will eat your carefully repaired pcb!!

 

[mvs sarma]

Has anyone ever had any luck de-potting a circuit? I bought 5 strobe light power supplys in need of repair off ebay. Of the 5, the three that were not pictured are fricken potted!

Will it re-melt at a temp that won't melt the rest of the circuit?

I had similar need 3 years back and a friend of mine in Bangalore (India) helpedme out. after seeing your post i had interacted with him .
as per him, soaking the item in Di Methile Chloride (forbid spell mistakes-(not a chemistry person) the potting compound will slowly soften. at room temp he says, it took a week. at say 80 deg celcious he hoped that this time will come down to 2.5days. peroidically we have to remove the softend portion. the plastic mould was not effected.

you may perhaps try out a small device first and then go for bigger ones.
however, we may have to wear gloves and protect our hand,which need not be told. I had got three dc-dc converters that are found in the ISDN CPEs unglued like this.

let us see.

Ps: Nigel -I too have seen epoxy used for potting in the units referred in my above experience.

 

[jpanhalt]

soaking the item in Di Methile Chloride (forbid spell mistakes-(not a chemistry person) the potting compound will slowly soften. at room temp he says, it took a week. at say 80 deg celcious

In the USA, it's known as dichloromethane, methylene chloride (not methyl choride), and methylene dichloride. It boils at about 40 C or so. I would not suggest trying to heat it to 80 degrees C. Most important, it is one of the active ingredients in solvent-based paint strippers, which are still available in the US (maybe not in California). Major toxic effects are neurological, hepatic, and of course, cancer.

One advantage of using a paint stripper is that they also contain methanol, which stabilizes the methylene chloride. Pure methylene chloride can also decompose to phosgene, which was used as a chemical weapon in WW I. John

 

[mvs sarma]

In the USA, it's known as dichloromethane, methylene chloride (not methyl choride), and methylene dichloride. It boils at about 40 C or so. I would not suggest trying to heat it to 80 degrees C. Most important, it is one of the active ingredients in solvent-based paint strippers, which are still available in the US (maybe not in California). Major toxic effects are neurological, hepatic, and of course, cancer.

One advantage of using a paint stripper is that they also contain methanol, which stabilizes the methylene chloride. Pure methylene chloride can also decompose to phosgene, which was used as a chemical weapon in WW I. John

Thanks John for the moderation and updation.

 

[Andy1845c]

The thing I worry about with soaking these with anything is the they are 12v strobe light supplys and have several transformers on the board. Couldn't soaking them in chemicals dissolve the insulation on the windings?

 

[mvs sarma]

The thing I worry about with soaking these with anything is the they are 12v strobe light supplys and have several transformers on the board. Couldn't soaking them in chemicals dissolve the insulation on the windings?

i get your point. we had torroid chokes in the modules we handled.

 

[jpanhalt]

The thing I worry about with soaking these with anything is the they are 12v strobe light supplys and have several transformers on the board. Couldn't soaking them in chemicals dissolve the insulation on the windings?

The insulation on the wire is probably safe. What will be affected are adhesives, tapes, and any soft plastics (not IC chips). I have tried to remove enamel from transformer wire with methylene choride and even more aggressive solvent mixtures. It doesn't work. John

 

[Andy1845c]

Hmm, well, if I get some time tomarrow I might try the heat and see what that does. If that dosn't work I will look into the solvent. I don't really have anything to lose I guess.

 

[mvs sarma]

Hmm, well, if I get some time tomarrow I might try the heat and see what that does. If that dosn't work I will look into the solvent. I don't really have anything to lose I guess.

I tried earlier scapping the potted surface with tip of a large 120w soldering iron.
it doesn't melt. scles might come but at that temp other components get burnt., i fear

 

[Andy1845c]

Well, I tried about 45 minutes at 250 degrees. It dosn't soften at all, but rather gets kind of brittle. You can then scrape it off with a knife. Wouldn't be so bad if these things wern't so darn big. Problem is I can't see whats under the potting, so I end up stabbing components and getting the kinfe point caught under 1/4 watt resistors and the like. I would certinly do far more damage then good removing it this way.

I do have some paint stripper around. Not sure whats in it though. I guess I could try that. Like I say, nothing really to loose.

 

[mvs sarma]

Well, I tried about 45 minutes at 250 degrees. It dosn't soften at all, but rather gets kind of brittle. You can then scrape it off with a knife. Wouldn't be so bad if these things wern't so darn big. Problem is I can't see whats under the potting, so I end up stabbing components and getting the kinfe point caught under 1/4 watt resistors and the like. I would certinly do far more damage then good removing it this way.

I do have some paint stripper around. Not sure whats in it though. I guess I could try that. Like I say, nothing really to loose.

yes, I understand your anxiety and need or urge to reach the circuit. i had this situation earlier. if the resistors and other things , can ofcourse be replaced, as long as the legend is ok. shorted diodes like, and if legend is also gone - reverse engg would be taxing the mind.

 

[Andy1845c]

Well, I tried the paint stripper I have, and it didn't do anything after several hours of soaking. It says it contains methylene choride: 79-09-2 I don't know what the numbers mean though?

Can you get just methylene choride? Or is paint stripper the closest I will come with out being a chemist?

 

[mvs sarma]

Well, I tried the paint stripper I have, and it didn't do anything after several hours of soaking. It says it contains methylene choride: 79-09-2 I don't know what the numbers mean though?

Can you get just methylene choride? Or is paint stripper the closest I will come with out being a chemist?

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