03-MAR-2024
Time to pull out the power supply unit, model H7883-YA, for visual inspection.
The very helpful DEC 3000 Models 600/600S AXP and 800/800S AXP Service Information guide describes the procedure thus:
(For some reason, the top two screws are T15 Torx, and the bottom ones are Phillips.)
(2)
There are signs of leakage and slight corrosion on the bottom of the power supply, which means it will now have to be taken apart for a closer look.
The power cord goes into this electromagnetic interference filter, a Delta Electronics part 15DRIW2A; Digital P/N 12-37780-01 B01.
The PSU comprises three boards connected together with a wiring harness. The first board takes AC input from the EMI filter via the power switch. The picture below shows the PSU from the top with the FCC screen removed so that the boards and the harness are visible.
This harness, P/N 70-30004-01, was subject to Field Change Order no. KN15-AA-O003 regarding possible emanation of smoke and soot. The FCO called for replacing the harness, which would bump the PSU revision to C01. I noted the C01 sticker on top of the original label on the front of the power supply, which meant that the harness had been previously upgraded and my unit should be smoke and soot free. At least as long as I don’t do anything daft, that is.
I pulled two boards out to check for leakage or any other damage. The third one was a bit of a faff to remove, so I went with inspection in situ. Since my ESD mat was fairly small, I extended it with a sheet of kitchen foil to have enough space for multiple boards.
Note how all these boards are single layer and entirely through-hole with not a single SMD component in sight.
The first board in the cage is the power input board MC1368B. Some nice-looking capacitors there from Nippon Chemi-Con; Dave Jones of EEVblog fame would have approved.
The top left section hosts three power and monitoring channels for the three system fans, which plug into the bottom-facing connector J7. Behind the heat sinks are circuits that supply the 3.45V regulator and SCSI devices through connectors J3 and J2, located at the rear of the power supply.
The third board, shown here inside the PSU cage, supplies the main board and SCSI devices via three rear-facing connectors.
Everything looks neat and tidy, no blown caps or anything. So what was that leak at the bottom of the unit, then? Must’ve been condensation.
With these checks out of the way, I can now put everything back together and gently turn it on…