VAX 4000 PSU (H7874) Schematics

[Aaron Jackson]

> On Thu, 7 Jun 2018, Aaron Jackson wrote:
>> The VAX turns on and the status LED stays on F. The DC lamp does not
>> illuminate on the PSU. 5V rail appears fine but there is nothing from
>> the 12V rail. There were some *very* dodgy looking caps which I have
>> replaced, and some *very* exploded MOSFETs, which I have also
>> replaced.
>
> If that's all that you replaced, no wonder it still doesn't work ;-)
> Usually shorted power transistors in SMPSUs also break one or more fusable 
> resistors, maybe some diodes, maybe the driver IC or transistors.
> So if you have anything that "exploded" in the power supply, be sure there 
> is more work to be invested that replacing the obious parts.
>
> Christian

Haha, okay, seems reasonable. I'll have to probe about a lot more
then. Not giving up quite yet, even though everything I have read about
this power supply has said that it is difficult to repair. So far, I
would agree with such a statement.

Thanks,
Aaron.