Glad the 23 PSU seems to be working again. My H7861 had a fault a couple of years ago where the 12V rail stopped working. It turned out to be a dead 555 timer, totally flat-lined. Perhaps it would be worth checking that in your H7861 if it is the MJE15030 that is blowing. At least it's a nice power supply to work on. :)
Aaron Charles via cctalk writes: > Update: I removed the H786 from the chassis, and set it up on the workbench > with loads on the +5 and +12. > No output. 320V across the half-bridge, but no +12 Startup. Found I had > forgotten to put a cliplead to the primary of the startup transformer. > Turned it on and it works... 5 and 12 volts into 1 ohm and 4.7 ohm > respectively. WTF. > > So I disconnected the PC supply, put the H786 back in, and it fired right up > (including the real-time clock) and I ran it for half an hour. > Go figure. Ain’t classic computers fun sometimes... > > > From: Paul Anderson > Sent: Saturday, March 30, 2019 3:26 PM > To: Charles ; General Discussion: On-Topic and Off-Topic Posts > Subject: Re: H786 power supply help wanted > > > Hi Charles, > > The H786 was standard for the 11/23, BA11-N. The H7861 was for the 11/23+, > BA11-S and had afrw more amps of +5 volts. > > I would start by looking at the electronic caps. > > I have a few extras here but am pretty busy for the next week or so. > > Paul > > On Sat, Mar 30, 2019 at 2:25 PM Charles via cctalk <cctalk@classiccmp.org> > wrote: > > I have a PDP-11/23+ and the power supply (H786) "last ran when parked" a > year or so ago. But there's no DC output at all today, and the fans are > running so there is AC power... > I also have the original H7861 that came with it, which had a blown chopper > transistor. I couldn't find anything else bad, so I replaced the transistor > and within a few seconds of running, it blew again. :( > > So I need some help - I've never been good at fixing switching supplies, not > to mention the high-side hazards. > The simplest solution would be just to replace it with a working unit. > Anyone got one to sell, hopefully cheap? :) > If not, can anyone fix one or both of mine? > > thanks! > Charles -- Aaron Jackson - M6PIU http://aaronsplace.co.uk/
