I do not understand what is going on here (in-circuit)...

[OpenCircuit]

I applied 15vdc to the Vcc on the riser pin as shown in the pic then traced the 15v through each SMD and found a massive drop to an erratic 3.7-4.2v reading as shown. Main IC is a CM6800TX from a power supply. Removed c24 and the electrolytic (situated on other side of board) and both give an expected reading. No ESR meter, but it is all I can do for now.

D4 failed a diode test and D2 tests fine, but diodes are almost impossible to test in-circuit I have found. These traces do not hold up well to de-soldering.

Obviously several things going on here with this riser board.  Thanks for any help analyzing this voltage drop-WHY?  Supposed to be or something likely failed.

[bob91343]

Not enough info.  What is this unit?  Do you have a schematic diagram?

[OpenCircuit]

GS800 (2013)...have not lucked across any diagrams. CM6800TX is the PFC controller I believe.

[fzabkar]

http://www.champion-micro.com/datasheet/Analog%20Device/CM6800T.pdf
http://www.champion-micro.com/datasheet/Analog%20Device/CM6800.pdf

[fzabkar]

GS800 (2013)...have not lucked across any diagrams. CM6800TX is the PFC controller I believe.

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[OpenCircuit]

"E206420 NE5000A   REV: P01 GP Corsair" are some of the markings on the PCB. Corsair GS Series GS800 80 PLUS® Bronze Certified Power. 2013..they redesign these frequently.

[OpenCircuit]

Bump

Can anyone make sense of the voltage drop?  Faulty or expected drop?

[james_s]

No idea about the voltage drop without a schematic, but I've found diodes to be very easy to test in-circuit. Sometimes other parts will interfere, but 99% of the time when diodes fail they fail short circuit. I use the diode check feature on my multimeter to test the forward drop.

[fzabkar]

Are you testing this APFC module out-of-circuit?

When it is installed on the main PCB, what voltage do you see on the output capacitor (presumably a 450V type)?

The module should drive a heavy inductor via an external power MOSFET. I would think that the problem would most likely be in that area.

I think that the Vcc supply for the module will most likely come from the rectified mains via one or two high value resistors. This supply is then augmented via a "bootstrap winding" on the DC-DC transformer or the PFC boost choke, as stated on page 20 of the datasheet. Alternatively there could be a 15V standby supply.

Another common fault is an open circuit in one of the startup resistors, or a dried out capacitor in the bootstrap supply.

[OpenCircuit]

I removed this riser board with the CM6800tx and applied 15vdc (typical) to the vcc pin on the riser board -see top image. I traced the voltage along this Vcc pin as I marked it in the top photo in my first post to show where the voltage drop is located.


I have +5vstby but no PFC boost on primary side; around 150vdc if I remember correctly. Switching FETS are fine. Applied 12vdc to secondary side and all voltages were in range. PGO was not as would be expected.

[fzabkar]

AFAICT, the point you have identified as "3.7v*" is a ground???

[OpenCircuit]

... is a ground???

the pad just to the left of C24 is the ground for the electrolytic on the opposite side (25v10uF). then off the C9 that ties directly back into the Vcc trace.