Hello TheSteve.
This is a tough one as it fails before it can gives any true error codes.
Have you tried communicating with the unit via GPIB?
Do any components get unusually warm/hot?
I know ram failures aren't uncommon in the 33120A so if you decide to just try replacing parts you might want to start there. It would be much more ideal to have a second unit so you can swap parts to narrow the failure down between the front display and the main board.
GPIB Card, not here right now the week next, the week after next I could do
Close by FAN LM2940CT(U1004 ) is Hot but OK(Temeprature Sensor is My finger)
There are four SRAM,
U105(256K-BIT SRAM 70ns) Floating Logic
U205(256K-BIT SRAM 25ns) Digital Waveform Data Synthesis
U404,405(256K-BIT SRAM 15ns) Waveform DAC
if RAM failure, It's U105(256K-BIT SRAM 70-NS) because U105 Control by SCX6206AK0(U103) IC-Gate Ary ASIC(Agilent Part# 1820-8907), What do you think?
I use 33120A a long intervals. Second Unit, humm, It's too hard to me
Anyway, It hasn't been long since Reading Schematic
I still want more time to consider opinions.
Thanx TheSteve.
coldframe.