Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

[stj]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

not always fakes,
some are pull's and they dont know if they worked to begin with.
most of the eproms i buy are pull's - not an issue if you know it.

[socketa]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

Well this 2.5V standby issue has nothing to do with the supervisor chip or the PWM/PFC chip, because i removed both of them (on the other PSU) and isolated the standby circuit from everything else, and it's still 2.5V
i checked all of the resistors, and they are all within tolerance, but i can't fully test the SMD caps because they have no values printed on them, but they are not shorted.
i see that they used a zener diode in the snubber. It's not shorted but maybe it's faulty in some way?
i altered the primary side of the schematic to match the standby that's in this PSU.

[socketa]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

The standby chip is good.
And it appears that all of the primary standby components are good also.
The TL431 tests good
I see that the TL431 needs 2.5V in order for it to turn on - could that be related to why there is only 2.5V standby?
There is a thyristor and a zener, in series, connected between the standby rail and the cathode of the TL431.
What is is the function of that additional circuitry?
Should it be latching?

[socketa]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

Fixed
It was either a leaky zener, or possibly a thyristor, in the OVP in the standby feedback (the zeners both still tested correct voltage)
Looks like the 2.5V standby is what happens when the opto is continuously turned on by the latched thyristor
The other PSU was working but had low PSON, so it wouldn't turn off with the mobo power button - but i didn't figure out why because i damage the board, by heating the cm6000 are too much (the PCB separated and cracked).
Also managed to short the primary cap of the one that i fixed, with exposed meter probes, which, after a couple of days of detective work, took out an SMD resistor that was going to the cm6000, and also caused the PWM OUT to not switch, which meant that although it was outputting a good voltage, and turning on the driver transistors, no significant current was able to pass through the SMD capacitor to the initial primary mosfet.
At least it didn't take two years to figure out this time.
Was quite lucky that the third, and last chip, that i tried worked, otherwise i may have suspected that it wasn't meant to pulse straight away and that it might have being due to some other issue.

[CapLeaker]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

Awesome and interesting finds! Some stuff was a bit hard going, but the key is to keep at it.

[socketa]

Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

True
Thanks for your interest/thoughts