Not sure if this belongs in repair or here, but recently I obtained a second Agilent 54831M scope.
Long story short, it was working, and I disassembled it to replace an encoder, and, while at it, fan upgrade on the AC/DC along with planning to replace the hard drive with a SSD in the near future.
After reassembling the unit, I couldn't get the unit to power at all. Assuming I forgot to connect a connector or crushed a wire, I removed the AC/DC supply to look for pinched wires. As expected, nothing is pinched, so I began disconnecting (assumed) unnecessary connectors to simplify the problem.
From what I'm seeing, disconnecting a five pin connector on the AC/DC seems to get the unit to power. This connector is marked: INH+, INH-, +5v AUX, DC OK, and AUX RTN.
Doing some research, INH is 'inhibit', but I'm uncertain what this means. Since it lists DC OK and AUX return, I'm assuming under normal conditions it's getting some sort of feedback that things are okay and to power the unit.
Also, if I measure the +5v AUX with this connector connected (and the unit doesn't power), I measure 5v. With it disconnected, and the unit powered, it measures a decreasing voltage (maybe 2 or 3 volts).
Now for some confusion: first off, the power button isn't working (but was when the unit was working prior to disassembling it). When the unit powers (with this five-pin connector disconnected), it powers immediately after inserting the power cable (fans come on) but doesn't actually boot; including the motherboard doesn't beep. After wiggling some wires around the fan control board, suddenly the unit booted normally (but still turned on by way of connecting power and the power button didn't do anything), the motherboard beeped, and I got a display. I recycled power several times and the unit worked every time (except the power button still didn't control anything nor did it light).
Figuring the problem would return and wanting to find the cause, Wanting to replicate the problem to find the root cause, I played around with the connectors on the fan control board, the Acquisition Board, etc... and now the unit is back to not powering unless I remove that five-pin connector.
Seeing how I managed to get the unit to boot with the motherboard beeping, it seems nothing is actually damaged.
My question is does anyone have experience with this type of power supply to know whether this five-pin connector is the brains to turning on the AC/DC? It seems the AC/DC is in complete shutdown because I don't get voltages anywhere. Once I disconnect the five-pin connector, all the voltages (5, 12, and -12) are present.