managed to fix a white screen / no boot error on an 34465A by swapping the Spear (U201).
As received, unit did power up, but no fan/USB/LAN, white display.
Upon initial optical inspection of the front panel module, I saw that the Spear had shorted solder balls, and the power management IC (TPS650701) got very hot.
Replaced the Spear, short circuits were gone. Unit powered on, fan spun up. B/W Keysight logo on the display with a progress bar running, but halting.
Two reboots and the progress bar made it to 100%, device seems to power up normally and functions.
Last instrument error displayed is "+822 Controller and measurement board serial numbers do not match", which went away after a factory reset (Edit: seems to persist, error queue was just emptied).
The Spear is quite warm to the touch, I think I am going to place one of those sticky heat sinks on it.
Is it worthwhile dumping the EEPROM?