DuoDock power supply issue

[elemenoh]

This DuoDock just clicks and spins the fan briefly when powered on. 5v measures okay but 12v only comes up to about 2.5v before coming back down to 0.

I've replaced the 100uf caps at C24 and C28 and (since one was bulging) the 330uf caps at C12 and C19. The other caps at least appear okay, but haven't been tested or swapped. 

Should I just replace all remaining caps or focus triage somewhere in particular?



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View attachment IMG_1753.mov

 

[elemenoh]

I swapped in a known-good MLB and had the same symptom.

Since I had them on hand I also replaced the 470µF/25v and 1,200µF 10v caps, but the issue remained.

The smaller caps are a PITA to get out. It was hard to get the channels clear even with solder wick and lots of flux.

Here's a cap map in case it's useful to anyone else.

 

[techknight]

One thing: You missed 3 other caps in the primary side of the power supply. This will cause your issue too. Especially the one to the left of the heatsink below the power transformer. 

Otherwise, power supplies that fail to start, or start and then shut down, take a look at the 6-pin opto-coupler in the center of your picture there. 

if there are no other bad caps or detected shorts on the secondary side of the PCB (like rectifiers, etc) then change out that optoisolator. 

Common problem with the TAM anyways. that, and the 3-pin standby switcher.