My HP 54200A has intermittently started to display a hardware failure error on power up. The built in diagnostics report no problems so I decided to read through the calibration and repair document. The entire document is all about the CRT and nothing more. I wondered if maybe an internal battery was starting to fail. There is absolutely no mention of a battery anywhere in any related document or google search. Finially I watched a tear down video and there actually is a battery soldered to one of the boards. It's some oddball 3.9v lithium battery and a replacement is $40! Does this sound like a battery failure or something else?
*quick edit
It now fails on power up every time and also fails every trigger/input test. Given the gradual decline and massive fail I'm going to look at the power supply caps.