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sutekh

Duo 280c Re-Cap

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Hello! I recently purchased a Duo 280c, and although it works (seller tested), I'm not going to run it until its very obviously leaking caps have been replaced. I'm no stranger to a soldering station, and have my cart ready for checkout on Mouser, but have hit a snag: I cannot for the life of me make out the silkscreen on my C6 cap, even after removing it. It's the slightly smaller 8mm cap behind the serial port. I've scoured the web and this forum for pics, videos, schematics, etc. to no avail. In a few pics it's tantalizingly close to legible, but not... quite! Any chance that any of you have a 280c (or similar) logic board handy and can help solve this mystery for me? Thank you!
 

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Mystery solved! Found an old post that mentioned the 280c logic board has 4 x 35v 100uf (check), 1 x 35v 47uf (check), 1 x 25v 33uf (check), and 1 x 25v 100uf (eureka!). I had all of the above in my parts bins, so recap complete.

My new friend gave me a bit of a scare today after buttoning it up though: Hung on the initial gray screen, even after numerous power-cycles. From my research trying to track down that cap value, I read numerous horror stories about leaking caps causing exactly that behavior on Duos xx(

Gravely concerned at this point, I opened it back up and started poking around with the DMM and scope. I couldn't find a schematic anywhere and the board is a forest of vias (who knows how many layers...), but while probing around in the DC-DC circuitry, I noticed that "DZ6" was open! :O D = diode, Z = Zener I assumed. The little SOT-23 SMD had "8Y" silked across the top, and a bit of googling suggested an SOT-23 packaged Zener diode thusly marked was perhaps an MMBZ5248? That I certainly didn't have, but I contacted a tech I'm friendly with at a local electronics repair shop and he did :) Booted right up after replacement. A $0.13 part almost ruined my day.

This particular failure mode was probably specific to my board, but if any of you are hanging on to failed Duo boards, replacing DZ6 might be worth a shot...
 

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Edited by sutekh

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Nice work! Do you mind pointing where DZ6 is? (Sorry, I can’t seem to see it in the pic)

 

I have a 210 with the exact same gray screen issue right now...

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Hmm... Looks like I didn't snap a pic before I put everything back together. Its on the other side of the board. Sames side as the caps about mid-way down.

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20 hours ago, sutekh said:

Sames side as the caps about mid-way down.

Sorry, this wasn't very clear and I'm past the edit window. DZ6 is on the other side of the board than the electrolytic caps, but once flipped, you'll find it on the "same side as the caps" meaning it's situated on that same half of the board roughly under them, not over by the RAM.

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