HP 9872T Trouble Shooting

[cruff]

I have two 9872C plotters, which are very similar, as you probably know. One of mine was stored where one or more mice took up residence, chewing one of the multi-conductor cables which carried the signals from the limit switches. On power up, the initialization sequence would cause the carriage to run to the extreme +Y direction and made a horrible noise until powered off.

If you haven't opened it up to check, you should do so to verify lack of cable damage, that there are no obviously bad capacitors. If you have the service manual, verify all supply voltages are correct.