AMS DMX board corrosion issue and bodged repair - advice sought

leadpoisoning · Sep 9, 2018

I just posted the other day about this delay i'm working on and while going through the other boards to check for seating problems and/or possible shorts or other issues i found this on the 77.4 card (DAC 3)!

Two big issues. Someone had 'built up' some thick solder pads on the edge connectors to force it to mate better with the backplane connector presumably due to a contact issue. the second issue is some severe corrosion (either from cap juice - more likely?) or else battery electrolyte which mysteriously migrated across the chassis ... the board resides about as far away from the board containing the battery as you can possibly get .. it seems to resemble battery electrolyte corrosion however.

the easier one first. the corrosion. I'm assuming the correct procedure would be to remove all the components in the region - scrub scrub scrub with mild acid (if it's battery alkali) and/or isopropanol etc - then replace any affected components with NEW (in case the existing ones are affected). Correct? And leave no stone unturned?

as for this 'pad' business ... i figure the two main options are to 1. leave it alone and hope the interloper who did this had good reason or 2. remove all traces of solder from the connector and then try to pry up or otherwise adjust the pins on the backplane connector to get things connecting better ... or ... option 3??

Thanks for your time and help

radardoug · Sep 10, 2018

That board looks to be cut short by the factory, and in fact should never have got past QC, but I suspect AMS QC wasn't the greatest. If you are having problems with it, then talk to David about a new board, or possibly replace the socket it fits in. David has those. As to the corrosion, I suspect someone has replaced the electro caps. AMS mostly used tantalums. Those electros can leak.

leadpoisoning · Sep 10, 2018

radardoug said:
That board looks to be cut short by the factory, and in fact should never have got past QC, but I suspect AMS QC wasn't the greatest. If you are having problems with it, then talk to David about a new board, or possibly replace the socket it fits in. David has those. As to the corrosion, I suspect someone has replaced the electro caps. AMS mostly used tantalums. Those electros can leak.

ok thanks for the info - all the previous repairs were done by him so i'm not sure i would want to go that route ... not to mention the USD 1400 required just to talk ... do you know what the 'cap juice' actually IS, chemically speaking? so i can have a better chance of cleaning it up properly??

i wonder if bending the backplane connectors out (somehow ... carefully) might yield a good result (i guess someone did this for a reason though)

leadpoisoning · Sep 10, 2018

under the caps ... yuck what a mess ...

i'm putting new tantalums in ... i hate it when people replace tantalums with electrolytics! They are there for a reason - people just don't want to pay out for the tants though i guess. However there wasnt' much sign of leakage under the electrolytics ... how to clean this mess up???

David Kulka · Sep 12, 2018

leadpoisoning said:
ok thanks for the info - all the previous repairs were done by him so i'm not sure i would want to go that route ... not to mention the USD 1400 required just to talk ... do you know what the 'cap juice' actually IS, chemically speaking? so i can have a better chance of cleaning it up properly??

i wonder if bending the backplane connectors out (somehow ... carefully) might yield a good result (i guess someone did this for a reason though)

I'm usually glad to talk with people for free. If we did a full refurb to that unit at some point in the past we wouldn't need to do the whole thing all over again, we could probably just work on the specific issues. In cases like this we can often do board swaps or repairs for people without having the whole unit sent over. And I think we have 1 or 2 spares in stock. But this is not to say it looks like a small or inexpensive repair. It could be very time consuming, and there might be other issues going on.

From your photos, it looks like at least some of the connections are in parallel, in which case a missing contact or two may not matter much. But if "solo" contacts are bad that's a different story and there may be no elegant fix. One workaround may be to find a spare or unused contact on the board, jumper to that one, and then modify the motherboard to match. Another way is to run hookup wire(s) with small connector (maybe a 3-pin EDAC) in line to allow removal, and route the problem connections to the motherboard that way.

In any case the socket on the motherboard should probably be replaced. We sell spares. You can probably find one elsewhere but make sure the leads are small enough gauge to pass through the PCB holes. This is a very tricky repair job — you need to be very careful and it would be smart to ohm out all the connections after replacement, before the first power up.

And clean up anything suspect looking on that board as well as you possibly can.

It’s very odd for that problem to appear on that board. I wonder how it happened. I’m sure the board wouldn’t have left our shop in that kind of condition. It may be beyond reasonable repair, but with a little luck you'll be able to get it going again.

leadpoisoning · Sep 12, 2018

David Kulka said:
I'm usually glad to talk with people for free. If we did a full refurb to that unit at some point in the past we wouldn't need to do the whole thing all over again, we could probably just work on the specific issues. In cases like this we can often do board swaps or repairs for people without having the whole unit sent over. And I think we have 1 or 2 spares in stock. But this is not to say it looks like a small or inexpensive repair. It could be very time consuming, and there might be other issues going on.

From your photos, it looks like at least some of the connections are in parallel, in which case a missing contact or two may not matter much. But if "solo" contacts are bad that's a different story and there may be no elegant fix. One workaround may be to find a spare or unused contact on the board, jumper to that one, and then modify the motherboard to match. Another way is to run hookup wire(s) with small connector (maybe a 3-pin EDAC) in line to allow removal, and route the problem connections to the motherboard that way.

In any case the socket on the motherboard should probably be replaced. We sell spares. You can probably find one elsewhere but make sure the leads are small enough gauge to pass through the PCB holes. This is a very tricky repair job — you need to be very careful and it would be smart to ohm out all the connections after replacement, before the first power up.

And clean up anything suspect looking on that board as well as you possibly can.

It’s very odd for that problem to appear on that board. I wonder how it happened. I’m sure the board wouldn’t have left our shop in that kind of condition. It may be beyond reasonable repair, but with a little luck you'll be able to get it going again.

ohhh thanks David - that's a pleasant surprise ... i had given up on you since none of my direct e-mails to studio electronics inquiring about repair were ever returned - and when i asked about the resistor value on GS you said you would help but never replied ... nice to know you're alive though - and thanks for your input ... and yes - it's got studio electronics stickers on the back of it

though maybe someone else was in it since. I'm going to do my best for now though - if you DO want to open communications on this I wouldn't say no ...

David Kulka · Sep 12, 2018

Sorry about the miscommunications, it wasn't intentional and I have no idea what happened. I changed personal and tech support email addresses a while back due to spam, and that might have been part of the problem. Emails to our support@ address go to both myself and our shipping gal and in the rare cases that I miss one or forget to reply to somebody, she usually reminds me or follows up herself. We really do try to get back to people promptly so I assure you and others here that this was just a fluke situation and not our usual mode at all.

I'll PM you with my current email address. If you still need info about the resistor run the question by me again and I'll get you an answer. Let me know the S/N and date of servicing so I can look it up. I'm overseas right now so it may take a day or two though.

AMS DMX board corrosion issue and bodged repair - advice sought

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