I've just done a teardown, clean, checkout, repair, modify and test of the H777 power supply from the PDP-11/04.
The H777 PSU
The main +5v @25A regulator PCB
The "MOS" regulator PCB, providing +/-15V @1A (and a smaller +5V @4A supply for use by a battery backup system)
At over an hour, the video is quite long, (and that's been distilled down from over 3 hours of recording).
But I think that anyone who is very interested in this topic, and especially anyone planning a similar exercise, would want to see as much detail as possible. Hence the long video.
For those not so inclined, the executive summary is:-
* Teardown and clean of the PSU.
* Reform the 3 large electrolytic capacitors.
* The 3900uF/6V cap on the 5V supply output is bad (which might be a chronic failure point for these units).
* A salvaged replacement cap is bodged into service.
* Testing reveals that the +/- 15V, and +5VB supplies (from the MOS regulator board) are good,
* But the +5V supply from the main regulator is producing no output.
* The +5V supply is found to be in current limit mode.
* When investigated out of the case, the +5V supply comes good.
* No obvious cause is found, but it's suspected that the replacement capacitor, and/or regulator module were reinstalled incorrectly.
Further suspicion falls on the interference fit of the PCB modules inside the unit.
Theory of failure is that this tightness is causing mechanical stress that may be affecting some components or solder joints.
* The two tall 560uF/20V capacitors on the MOS regulator PCB were replaced with modern 1000uF/25V caps that are much shorter, and so eliminate the interference between the PCBs.
* Unit is reassembled and all voltages are good.
* A connector and cable harness are made to attach the PSU to a set of dummy loads.
* All supplies operate satisfactorly at near rated load (but only at about 19A on the +5v supply).
The need for a better dummy load for the +5V supply is clear.
The video:-
https://youtu.be/MpV6pyaxZ6MLinks:-
Mattis Lind's (DatorMuseum in Sweden) PDP-11/04 restoration, with similar H777 PSU issues:-
http://www.datormuseum.se/computers/digital-equipment-corporation/pdp-11-04 Documentation resources at BitSavers:-
861B Power controller:-
http://www.bitsavers.org/pdf/dec/powerSupply/EK-861AB-OP-001_861-A_B_C_D_E_F_Power_Controller_Users_Manual_Nov76.pdfBA11-L mounting box (used for both 11/04 & 11/34, contains extensive H777 theory of operation)
http://bitsavers.trailing-edge.com/pdf/dec/unibus/EK-BA11L-TM-001_Oct77.pdfhttp://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-11-HBKEF-A-D%20BA11-K%20Mounting%20Box%20Manual.pdfPDP-11/04 Engineering drawings (H777 PSU starts at P104):-
http://bitsavers.org/pdf/dec/pdp11/1104/MP00019_1104_EngrDrws_Feb78.pdfPDP-11/34 Engineering drawings (H777 PSU starts at P183. Component overlay is more legible):-
http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1134/MP00082_1134_Vol2_Sep76.pdf