Help repairing Voltrex SMPSU for HP41501A

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I've a HP41501A which has a dead power supply... the PSU is a self-contained unit, manufactured by Voltrx Corp of Japan. I've not been able to find a schematic or even any details of this unit, marked 'FPS2 D2161' and dated 1993-9.

Checking the power route from the AC socket, the bridge rectifier is OK and providing +250v DC. There is a Harris HV3-2405E-5 taking mains and providing +15v to a IR2110 mosfet driver. But the inputs to this are from a vertical board (see pic) which is potted and appears to have a single IC in it, plus a few SMD components. And those gate signals are sitting at 0v all the time.

The black potted thing is marked 'Voltrx CAP-3001C' and I did try swapping it for another from another board I have, but that made no difference. I've also replaced all the electrolytics, so I'm a bit stumped.

If anyone's any knowledge of this PSU, and possible fixes, I'd be really grateful!!!

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When I posted the above today I really thought I had little hope of fixing the problem. With no documentation or info on the power supply, it was not looking good. It was sold as 'not working' on eBay and so was cheap, as was the 41501A that I had also bought cheap because it had no power supply. The odds of finding two allegedly broken parts of a unit that could be fixed and put together to make a working one (which sell for $5000 or so) was remote.

The power supply consists of 4 boards: the base unit in the pic above, a top unit and two interconnecting PCBs. One of the interconnecting PCBs, visible at the top of the picture below, runs power and a few control signals to the other. I had not disconnected it before as it was quite firmly attached to the top board. But today it came loose as I was trying to put the thing back together again. I noticed that it could go either way round! The connectors each end of it were identical. But the silk screen of the two PCBs gave the plug/socket numbers, which would, I thought, indicate the correct connection. Which was the opposite way round to what it had been all along...

Putting it back together and plugging it in and switching on, hoping it would not emit smoke... the fans started working! And when fitted into the 41501A, that powered up. And so connecting the 4155B and 41501A together I now get the HPSMU and PGU's recognised... how good is that.

Moreal of the story... check *everything* even the obvious.