Bestec ATX-250-12E Rev F1 - Its.... A L I V E !

[JEWilson]

Hi

Pulled this from an Advent 3316 D1 Case
This PSU is good - tested (at least) with a PSU tester.

I have another Advent 3117 D1 Case - same PSU.
I found this PSU dead as well as the mobo.
Have seen comments in the forums here indicating 5VSB
problems with these PSUs (going to 12V) and killing
the mobo in the process.

So far...
I have tested for any shorts to ground, visual inspection
for bad caps - anything physically loose and the like.
Result - nothing immediately apparent.

Have replaced the PSU in failing 3117, no start up
Suspect - start up logic and/or VID logic in the CPU VRM
consistent with fault described in the forums.
The regulator is a Intersil ISL6556CBC. Replace reg?

Any other help, insight and advice greatly appreciated

[999999999]

Re: Bestec ATX-250-12E Rev F1 - Its.... A L I V E !

Clear CMOS
Check Battery voltage

What exactly happens when there's "no start up"? Does PSU remain running? Do all PSU voltage levels seem acceptible? If so, Check voltage at the output from the VRM, so long as the board is receiving live 12V power (assuming 12V input based VRM), and the processor is installed, it should be outputting reasonably near the target voltage regardless of whether the system posts or not. IE- system initialization, bios, nor chip logic (outside the controller itself) are not (normally) prerequisites for the VRM controller to output to CPU so long as a processor is installed to give it the initial pin input to set a voltage (and produce it).

I doubt the regulator (controller IC) failed, at least not all by itself. Supposing it might be the 5VSB problem you mentioned, that would not effect the VRM controller either as it has no 5VSB supply.

[JEWilson]

Re: Bestec ATX-250-12E Rev F1 - Its.... A L I V E !

Hi

Y - concur

However, the PSU and the mobo remain dead.

I have the mobo on a bench and attempt to short the
PS start pins on the board. As such there is no power
to the board and have tested this to be the case with
a diagnostics card. No voltage readings whatsoever.

So... replaced the PSU with known good.
Problem persists.

Checked CPU regulator - getting no supply
as well as no VID being present.

Suspect soft-start in the regulator at fault or reg
failed entirely. As no shorts to gnd - suspect power
devices such as MOSFETs ok.

Any thoughts, insight and advice appreciated
Thanks

[999999999]

Re: Bestec ATX-250-12E Rev F1 - Its.... A L I V E !

The board not starting doesn't necessarily have anything to do with VRM subcircuit. If you completely desoldered the entire VRM subcircuit and removed it, shorting the motherboard power-on pins together would still turn the PSU on.

With a known good PSU plugged into the board, use thin wire/paperclip/etc to short the PS-On pin to ground at the ATX connector. See if PSu stays on without keeping that shorted, or with it shorted. Measure voltages from PSU if it stays running either way (the PSU, nevermind if the board is posting yet). Next measure voltage at VRM output (leg of last inductor will suffice if it's accessible above-board so you don't have to be flipping the board over).