VAX 4000 PSU (H7874) Schematics

I have one or two mostly new 4000 supplies here, plus two working 4000's. Did not know until recently this was an issue, I guess I have been lucky. b On Fri, Jun 8, 2018 at 9:04 AM, Holm Tiffe via cctalk <cctalk at classiccmp.org > Aaron Jackson via cctalk wrote: > > > > 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. > > Difficult to repair? Probably since it is the worst switching PSU Desing > I ever meet, at least from seriveability and the mechanical point of view. > > I own an 4000/300 with an working again PSU (after some capacitor > changes) and I habe an PSU from a friend here..its works sometimes, > mostly not. > > Regards, > > Holm > > -- > Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe, > Freiberger Stra?e 42, 09600 Obersch?na, USt-Id: DE253710583 > info at tsht.de Fax +49 3731 74200 Tel +49 3731 74222 Mobil: 0172 8790 741 > >