glitch
Veteran Member
full writeup here: http://www.glitchwrks.com/2019/06/05/pdp1110-psu-repair
A bit over a year ago, I finally repaired a RX211 controller while working on a friend's PDP-11/34a. The RX211 was destined to live in my PDP-11/10S. After getting the RX211 tested and running, I started bringing up the 11/10; naturally, something let go in the power supply and smoked, taking the machine down. Well, I finally got around to fixing it! The problem turned out to be a shorted bridge rectifier in the 5411086 board, which provides +15 VDC, LTC, and AC LO/DC LO. It shorted hard enough that it blew traces off the edge connector:
Ouch! I repaired the regulator, went ahead and replaced the +15 V output filter cap with a new low ESR type (the original smelled like leaking electrolyte), and patched up the burned connector. I ended up cutting the edge connector contacts off and soldering on a wire pigtail: as luck would have it, there's a Mate-n-Lok on the short pigtail between the AC transformer and the 5411086 edge connector socket.
I also took the opportunity to put a 15 A fuse inline with the AC supply to the 5411086. If your 5411086 is still working fine, you might want to do this before traces get burned away! It'd be easy to make up a pigtail with the fuse holder and two Mate-n-Lok connectors on each end, so that the wiring harness isn't permanently modified. The required connectors are still readily available (mine came from Mouser). The other regulator modules in the H765 power system could also suffer from a shorted rectifier blowing traces out, but they all use Mate-n-Lok connectors instead of edge connectors, so the damage would be easily repaired.
With the supply repaired and bench tested, I fully cleaned the rest of the 11/10 and put it back together. Success! Everything still works, the shorted rectifier didn't harm the rest of the system! Here's a few pictures:
From the front, powered off.
Minimal board set: CPU, bootstrap/terminator, console connector, core subsystem, and grant cards.
The M9312 console emulator, running on a VT220.
A bit over a year ago, I finally repaired a RX211 controller while working on a friend's PDP-11/34a. The RX211 was destined to live in my PDP-11/10S. After getting the RX211 tested and running, I started bringing up the 11/10; naturally, something let go in the power supply and smoked, taking the machine down. Well, I finally got around to fixing it! The problem turned out to be a shorted bridge rectifier in the 5411086 board, which provides +15 VDC, LTC, and AC LO/DC LO. It shorted hard enough that it blew traces off the edge connector:
Ouch! I repaired the regulator, went ahead and replaced the +15 V output filter cap with a new low ESR type (the original smelled like leaking electrolyte), and patched up the burned connector. I ended up cutting the edge connector contacts off and soldering on a wire pigtail: as luck would have it, there's a Mate-n-Lok on the short pigtail between the AC transformer and the 5411086 edge connector socket.
I also took the opportunity to put a 15 A fuse inline with the AC supply to the 5411086. If your 5411086 is still working fine, you might want to do this before traces get burned away! It'd be easy to make up a pigtail with the fuse holder and two Mate-n-Lok connectors on each end, so that the wiring harness isn't permanently modified. The required connectors are still readily available (mine came from Mouser). The other regulator modules in the H765 power system could also suffer from a shorted rectifier blowing traces out, but they all use Mate-n-Lok connectors instead of edge connectors, so the damage would be easily repaired.
With the supply repaired and bench tested, I fully cleaned the rest of the 11/10 and put it back together. Success! Everything still works, the shorted rectifier didn't harm the rest of the system! Here's a few pictures:
From the front, powered off.
Minimal board set: CPU, bootstrap/terminator, console connector, core subsystem, and grant cards.
The M9312 console emulator, running on a VT220.
