I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I don't
have a circuit otherwise I might have just knocked up a new one - it's not
terribly complicated.

--
*Any connection between your reality and mine is purely coincidental

Dave Plowman London SW
To e-mail, change noise into sound.

Dichloromethane is the 'canonical' solvent. Also nitromethane - as
used in model glow engine fuel. There is also the 'hammer and chisel'
method.

here's a thread (about depotting a hifi amplifier module) from which
you might be able to scrape a bit more info.

http://www.diyaudio.com/forums/showthread/t-58618.html


HTH
J^n

jkn wrote:
Dichloromethane is the 'canonical' solvent. Also nitromethane - as
used in model glow engine fuel. There is also the 'hammer and chisel'
method.

here's a thread (about depotting a hifi amplifier module) from which
you might be able to scrape a bit more info.

http://www.diyaudio.com/forums/showthread/t-58618.html


HTH
J^n

I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.


NT

On Mon, 27 Apr 2009 14:39:09 +0100, Dave Plowman (News) wrote:

I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I don't
have a circuit otherwise I might have just knocked up a new one - it's not
terribly complicated.

Urgh, can't stand it when manufacturers do that. I've had some luck in
identifying passives in-circuit via the solder side and then grinding the
resin away to reveal details of semiconductors, but it's risky - very easy
to erase markings.

Do you know what the module's *supposed* to do - i.e. can you not ditch
it altogether and rig up an alternative that does the same job?

In article
,
wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.

Excellent - I'll give it a try.

--
*El nino made me do it

Dave Plowman London SW
To e-mail, change noise into sound.

In article . com,
Jules wrote:
On Mon, 27 Apr 2009 14:39:09 +0100, Dave Plowman (News) wrote:

I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I
don't have a circuit otherwise I might have just knocked up a new one
- it's not terribly complicated.

Urgh, can't stand it when manufacturers do that.

It is subject to - I'd say - severe impact energy.

I've had some luck in identifying passives in-circuit via the solder
side and then grinding the resin away to reveal details of
semiconductors, but it's risky - very easy to erase markings.

Yes - I'm guessing it's the output device that has failed, but would need
to identify it.

Do you know what the module's *supposed* to do - i.e. can you not ditch
it altogether and rig up an alternative that does the same job?

I can buy a new module for 60 quid - but it's not worth it. So anything
other than a small amount of work needed to fix it will mean the whole
lot's junk.

--
*Ambition is a poor excuse for not having enough sense to be lazy *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I don't
have a circuit otherwise I might have just knocked up a new one - it's not
terribly complicated.

Not a damned thing you can do. Its easier to repair a chip...

jkn wrote:
Dichloromethane is the 'canonical' solvent. Also nitromethane - as
used in model glow engine fuel. There is also the 'hammer and chisel'
method.

here's a thread (about depotting a hifi amplifier module) from which
you might be able to scrape a bit more info.

http://www.diyaudio.com/forums/showthread/t-58618.html


HTH
J^n
Nitromethane wont touch epoxy. Which is why we use it as a proofer
against nitromethane containing fuels..

Dave Plowman (News) wrote:
In article
,
wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.

Excellent - I'll give it a try.

Dont hold your breath. I've *cured* soft epoxy using a warm oven..

On 27 Apr, 14:39, "Dave Plowman (News)" wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components?

Not much. "Potting compound" is such a useful substance that it's
generally used to both pot components, and to make much of those
components in the first place. It's very difficult to extract things
in a way that leaves recognisable forensics.

Where I've done this before and known broadly "what" but not "what
value" I've usually ended up baring the solder-side enough to see the
circuit, then slicing the component side apart into anonymous black
cuboids that I could measure the values of individually. This takes
about as long as you'd expect...

If you're just replacing an output stage, then simply guess at what a
good design would be and try it. Bipolar or VFET, + or -? Hfe isn't
usually critical enough to care. Swap a whole matched pair or H-bridge
if you have to.

Nitromethane wont touch epoxy. Which is why we use it as a proofer
against nitromethane *containing fuels..

Being a (somewhat ex-) aeromodeller, I have wondered about this
myself. However I definitely read it originally in an old copy of
either aeromodeller and/or RCM&E, as well as having seen it referred
to since. You'll see that the thread I referred to also independently
mentioned using nitro. Perhaps potting epoxies are different? I would
be interested to know more...

J^n

On Mon, 27 Apr 2009 07:26:38 -0700 (PDT), jkn
wrote:


Dichloromethane is the 'canonical' solvent. Also nitromethane - as
used in model glow engine fuel. There is also the 'hammer and chisel'
method.


Nitromors or polystripper will do.

But IGWS will strip painted components if it gets to touch them.

Derek

Anything that could
dissolve it while leaving a chance of identifying the components?

No. That black stuff is a bugger. Best bet? Chisel. Been there, done that.

I
don't have a circuit otherwise I might have just knocked up a new one
- it's not terribly complicated.

D'oh! That's why they encased it in epoxy ;-)

Cripes, many years ago went down this path. Basically destroyed dozens of
"ranson holding" items to extract the underlying circuit. Hacksaws and
chisels worked best.

Oh, the ransom holding company had gone bust, taking a couple of million
quids worth of IP with them. Fair game. Sorted.

Al.

On Apr 28, 1:39 am, "Dave Plowman (News)"
wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components?

40 years ago we used a product to dissolve potted epoxy. We mainly
used it to take apart epoxy potted transformers so that we could
rewind them. It would dissolve fingers etc and had to have a layer of
water over the top in its container. It would dissolve almost anything
except for metal and glass, and of course it took the paint off the
components. We were able identify the components and test them and
manufacture our own circuits, which we potted in epoxy.

I can't remember the name of the product but this site may help:
http://www.best-chemical.com/ind_elect2.htm

The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.

Excellent - I'll give it a try.

Dont hold your breath. I've *cured* soft epoxy using a warm oven..

Indeed, and last year I used boiling water to set some quickly. Its
one apparent contradiction I've never gotten to the bottom of. All I
can say is it worked. This was in the 90s when I knew little about the
stuff. If anyone can explain, please do!


NT

In article
,
Andy Dingley wrote:
On 27 Apr, 14:39, "Dave Plowman (News)" wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components?

Not much. "Potting compound" is such a useful substance that it's
generally used to both pot components, and to make much of those
components in the first place. It's very difficult to extract things
in a way that leaves recognisable forensics.

Oh dear. But I'm not surprised.

Where I've done this before and known broadly "what" but not "what
value" I've usually ended up baring the solder-side enough to see the
circuit, then slicing the component side apart into anonymous black
cuboids that I could measure the values of individually. This takes
about as long as you'd expect...

The solder side is clear, and there are only a handful of components. But
I'm not going to waste much time on it.

If you're just replacing an output stage, then simply guess at what a
good design would be and try it. Bipolar or VFET, + or -? Hfe isn't
usually critical enough to care. Swap a whole matched pair or H-bridge
if you have to.

I'd guess it's an Triac.

--
*No sentence fragments *

Dave Plowman London SW
To e-mail, change noise into sound.

To make you feel happier many modern car common rail turbo diesel
engine management computers are potted... and I'll let you figure out
how much the dealers want to charge for a recent model replacement. It
isn't pretty.

Try comp.sci.electronics... or one of the military forums... A10 is
good for frustration relief... weeds... energy salesmen...

On Apr 27, 2:39*pm, "Dave Plowman (News)"
wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I don't
have a circuit otherwise I might have just knocked up a new one - it's not
terribly complicated.

Google "potting compound removal". First hit has tips for mechanical
removal and links to chemicals used for removal.

MBQ

On Apr 27, 11:24*pm, wrote:
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article
,
* wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.

Excellent - I'll give it a try.

Dont hold your breath. I've *cured* soft epoxy using a warm oven..

Indeed, and last year I used boiling water to set some quickly. Its
one apparent contradiction I've never gotten to the bottom of. All I
can say is it worked. This was in the 90s when I knew little about the
stuff. If anyone can explain, please do!

A short exposure to heat will set epoxy quickly.

Prolonged exposure to dry heat will not do anything to set epoxy.

Prolonged exposure to heat+moisture will destroy set epoxy
(particularly the rapid-set type).

So simmering overnight would probably solve Dave's problem (but I
wouldn't want to bet on the functionality of the PCB afterwards).

Man at B&Q coughed up some electrons that declared:

On Apr 27, 2:39*pm, "Dave Plowman (News)"
wrote:
I have a PCB I'd like to repair - but the whole thing on the component
side is potted in what appears to be epoxy resin. Anything that could
dissolve it while leaving a chance of identifying the components? I don't
have a circuit otherwise I might have just knocked up a new one - it's
not terribly complicated.

Google "potting compound removal". First hit has tips for mechanical
removal and links to chemicals used for removal.

MBQ

The firm I used to work for had to do a bit of depotting (on their own kit,
to check for manufacturing quality etc).

There is a specific depotting chemical, but it does tend to turn the
compound rubbery rather than wash it of. So the use of a sharp scalpel will
still be required, though it is easier.

On 28 Apr, 12:57, Tim S wrote:

The firm I used to work for had to do a bit of depotting (on their own kit,
to check for manufacturing quality etc).

When I used to do that, we potted the "test" units up with a removable
potting compound (silicone rather than filled epoxy, AFAIR). Although
the units were sealed well enough to survive in service (chemical
splash more than impact), it was still possible to re-open them
afterwards with a scalpel and peel them out. Then they'd often have
small changes made (hybrid circuits manually de-soldered, swapped and
re-soldered), potted up again and would go back into service.

On Tue, 28 Apr 2009 04:35:29 -0700 (PDT), Martin Bonner
wrote:


Prolonged exposure to heat+moisture will destroy set epoxy
(particularly the rapid-set type).

Thanks - that explains my failure at repairng the kettle spout seam.

--
Geo

On Tue, 28 Apr 2009 04:35:29 -0700 (PDT), Martin Bonner
wrote:

On Apr 27, 11:24*pm, wrote:
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article
,
* wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.

Excellent - I'll give it a try.

Dont hold your breath. I've *cured* soft epoxy using a warm oven..

Indeed, and last year I used boiling water to set some quickly. Its
one apparent contradiction I've never gotten to the bottom of. All I
can say is it worked. This was in the 90s when I knew little about the
stuff. If anyone can explain, please do!

A short exposure to heat will set epoxy quickly.

It might, but it also might not, it might destroy it.

Prolonged exposure to dry heat will not do anything to set epoxy.

It will in many cases raise the Tg - the glass transition temperature.
Post cure controlled heat is often used in high end applications of
epoxy (aerospace/motorsport) to ensure long term stability under high
temperature conditions.

Prolonged exposure to heat+moisture will destroy set epoxy
(particularly the rapid-set type).

Depends on the temperature and there is nothing particularly special
about heat and moisture, heat and no moisture can also degrade epoxy.


--

The Natural Philosopher wrote:
Martin Bonner wrote:
On Apr 27, 11:24 pm, wrote:
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.
Excellent - I'll give it a try.
Dont hold your breath. I've *cured* soft epoxy using a warm oven..
Indeed, and last year I used boiling water to set some quickly. Its
one apparent contradiction I've never gotten to the bottom of. All I
can say is it worked. This was in the 90s when I knew little about the
stuff. If anyone can explain, please do!

A short exposure to heat will set epoxy quickly.

Prolonged exposure to dry heat will not do anything to set epoxy.

Prolonged exposure to heat+moisture will destroy set epoxy
(particularly the rapid-set type).

So simmering overnight would probably solve Dave's problem (but I
wouldn't want to bet on the functionality of the PCB afterwards).

Most electronics are guaranteed to a storage temp of about 125C.

70C operational is typical commercial.

So simmering might well work.

its a definite risk though, any component less than perfectly sealed
will saturate. I'd want to give it a long hot dry out time, a week or
so.


NT

wrote:
The Natural Philosopher wrote:
Martin Bonner wrote:
On Apr 27, 11:24 pm, wrote:
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
I once turned epoxy to soft putty using steam. Almost all components
would survive that ok, given a long dry out afterwards.
Excellent - I'll give it a try.
Dont hold your breath. I've *cured* soft epoxy using a warm oven..
Indeed, and last year I used boiling water to set some quickly. Its
one apparent contradiction I've never gotten to the bottom of. All I
can say is it worked. This was in the 90s when I knew little about the
stuff. If anyone can explain, please do!
A short exposure to heat will set epoxy quickly.

Prolonged exposure to dry heat will not do anything to set epoxy.

Prolonged exposure to heat+moisture will destroy set epoxy
(particularly the rapid-set type).

So simmering overnight would probably solve Dave's problem (but I
wouldn't want to bet on the functionality of the PCB afterwards).

Most electronics are guaranteed to a storage temp of about 125C.

70C operational is typical commercial.

So simmering might well work.

its a definite risk though, any component less than perfectly sealed
will saturate. I'd want to give it a long hot dry out time, a week or
so.


hehe. Story of the day. We have several Sony set top boxes for digital TV..


One in teh lving room, one in my 'den' and one in the bedroom.

"Darling, wheres the ***ing controller fr the bedroom"

"Cant find it. I am sure it was on the bedspread and diuvet"

"Well where is that, the bed is stripped"
"In the ashing machine"....

Yup she had WASHED the controller.

So I took the Den one and took the batteries out of the other one and
shoved it in the airing cupboard - a shot to nothing - and forgot about
it..till I had occasion about 3 weeks later to go to the cupboard again.

By golly, fresh set of batteries, and it worked!

..






NT

In message , The Natural Philosopher
writes
its a definite risk though, any component less than perfectly sealed
will saturate. I'd want to give it a long hot dry out time, a week or
so.


hehe. Story of the day. We have several Sony set top boxes for digital TV..


One in teh lving room, one in my 'den' and one in the bedroom.

"Darling, wheres the ***ing controller fr the bedroom"

"Cant find it. I am sure it was on the bedspread and diuvet"

"Well where is that, the bed is stripped"
"In the ashing machine"....

Yup she had WASHED the controller.

So I took the Den one and took the batteries out of the other one and
shoved it in the airing cupboard - a shot to nothing - and forgot about
it..till I had occasion about 3 weeks later to go to the cupboard again.

By golly, fresh set of batteries, and it worked!

When my wife washed her mobile, some of the legs on the ICs hadn't just
corroded, they had dissolved away


--
geoff