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
