Data I/O Unisite PSU Issue (It don't work)

[martinator]

Hi,
I've got a Data I/O Unisite that has a power supply problem.

It will try to kick out some voltage for about 2 seconds and will then shut down.

The initial power-on whine sounds normal like it's trying to get going (no screeching or anything before it shuts down)

There's no visible damage or strange smells.

There's no discernible shorts between the supply outputs and the circuit boards in the Unisite itself don't seem to have any shorts or visible damage.

I'm slowly trying to isolate parts in the supply from each other so I can test them. I haven't yet found any dead shorts with the transistors/diodes.

My guess is shorted transformer windings or maybe a hybrid board problem but maybe someone else knows more or maybe even has a schematic or knows what I should check first?
Could the MOV's cause a problem without exploding like they usually do when bad?

I had planned on replacing the electrolytic capacitors and the metallised paper caps as they crack with age anyway but I found no faulty ones amongst the old.
There's more photos here http://s1200.photobucket.com/user/apprenticemart2/library/Unisite

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[helius]

Is CR20 supposed to be missing?

[martinator]

Yes. I've started to remove/lift one end of some parts so I can measure things/test them.

The 2 and 3 legged devices on the periphery are

CR17 - PHS2402
CR20 - MBB2045CT
CR21, CR22 - BYW29
CR36 - MCB69-3
Q11 -IRF533
CR24, CR25 - BYV73
Q1 - BUP22C
Q2 - TIP50

[helius]

There's a Data I/O yahoo (ugh) group: https://beta.groups.yahoo.com/neo/groups/Data_IO_EPROM/
You might be able to search for PSU issues there. I think the Unisite shares its design with the 2900/3900/3980, so it may have the same PSU.

[martinator]

Yep, already joined the group and asked there.
I will check the documentation for the 2900/3900/3980.Thanks.