Hi folks,
These PSUs seemed to be a default go-to for anyone back in the 80s who needed a +5/+12/-12 ~2A supply for anything from a computer (Osborne), disk drive (TRS80, Memotech FDX) or video terminal (Falco), and there's a good schematic and parts list available, even a servicing guide. But! Nothing I've found says what the main chopper transistor is other than 'Q2' - 'Power transistor'.
I have one here out of an STC Executel 3910 'executive telephone' that's producing little to no output even with a load attached and I've run out of things to check so I'm looking for ideas. Some caps on it had burst when I first uncovered it, as had its RIFA .1uF mains filtering cap so I replaced them all with modern and reasonably similar sized equivalents. Ohmmeter across the outputs with it disconnected doesn't show any shorts and because I can I've removed all the major components to test them, they all look OK. The only things I've not looked at fully yet are the small resistors, major transformer and coils.
Anyone? I know the Executel itself powers up since I've got another 8151 PSU that works but I don't want to start pulling that to bits. Yet :)
These PSUs seemed to be a default go-to for anyone back in the 80s who needed a +5/+12/-12 ~2A supply for anything from a computer (Osborne), disk drive (TRS80, Memotech FDX) or video terminal (Falco), and there's a good schematic and parts list available, even a servicing guide. But! Nothing I've found says what the main chopper transistor is other than 'Q2' - 'Power transistor'.
I have one here out of an STC Executel 3910 'executive telephone' that's producing little to no output even with a load attached and I've run out of things to check so I'm looking for ideas. Some caps on it had burst when I first uncovered it, as had its RIFA .1uF mains filtering cap so I replaced them all with modern and reasonably similar sized equivalents. Ohmmeter across the outputs with it disconnected doesn't show any shorts and because I can I've removed all the major components to test them, they all look OK. The only things I've not looked at fully yet are the small resistors, major transformer and coils.
Anyone? I know the Executel itself powers up since I've got another 8151 PSU that works but I don't want to start pulling that to bits. Yet :)