Overvoltage warning: calibration issue or device failure? SUA1000RM2

[BillP]

I have two APC SUA1000RM2U units that are ancient 1999 models that keep going and going. Both of these units are plugged into the same power circuit, and even the same receptacle.

The other night, one of the units briefly switched to backup power, then lit the 'overvoltage' light.

I measured the wall outlet voltage with a Fluke RMS DMM and the wall voltage is correct at approx 121v (and no other UPS units show the warning).

Within the AP9617 web interface, the unit shows the input voltage as being 138 volts. The same values show up via telnet, or even at the serial interface of the UPS, via SmartCable serial. I have the latest firmware that's available, and I re-flashed the firmware for both the UPS and the 9617 card (with the same version) but that made no difference. The site wiring lite is not lit and I did a full shutdown/restart several times. All other voltages are normal.

I am familiar with using the SM command line, and was curious if the input voltage measurement reading is simply a calibration issue caused by corrupted firmware?

At the command line, I could not get it to goto PROG mode, despite giving the correct inputs of 1 and 1 two seconds apart. Is there is something different for this specific model??

I am assuming that this sudden change was caused by a component failure. I do electronics repair and found the schematic for the unit, so my plan is to dig into it. But if it's just a calibration issue, that would be somewhat easier, as it's no picnic to have to remove one of these units from the rack for service.

An interesting thing I noticed is that if I do a self-test, the overvoltage light goes off, the test passes, and then the light comes back on after the test.

[BillP · Accepted solution]

Thanks. Obviously you want to check for a simple firmware fix before desoldering components.

This unit is so old it should be fairly easy to work on, as components were a lot bigger in 1997 when this beast was made.