OK, I posted it here: https://robs-old-computers.com/2020/03/29/h7874-power-supply/
> -----Original Message----- > From: Robert Armstrong <b...@jfcl.com> > Sent: 29 March 2020 15:44 > To: r...@jarratt.me.uk; 'General Discussion: On-Topic Posts' > <cct...@classiccmp.org> > Subject: RE: H7874 power supply > > > Rob Jarratt >robert.jarr...@ntlworld.com> wrote: > > I reverse engineered the schematic of the 12V output board. I don't > >know if that would be of any use? How correct it is I don't know. > > Sure, if you don't mind sharing. Everything helps. > > Looks like there are five separate PCBs in there. There's one long, skinny one > that's obviously the AC input and rectifier board, which probably produces > something like 300VDC for the regulator boards. There are two similar but not > identical boards with huge heat sinks that are obviously the output regulators. I > think this PS has +5, +3.3, +12 and -12 volt outputs, but I've no idea which board > does which. > > And then there's a giant PCB, almost 11" square, covered with opamps, 74LS > logic and discrete parts. There are filter caps, a transformer, and switching > transistors on this board too so it obviously produces yet another power output > for something. Oh, and I think this cabinet has variable speed fans, right? SO > there's probably a fan speed controller on here as well. > > You'd think that will all this logic it could at least have some LEDs or > something to tell me which output has failed, but it doesn't seem like it. > > Thanks > Bob
