No display of HP/Agilent 6812 AC power source

[heize0]

I have an HP/Agilent 6812 AC power source.
There is no display and only shift can sometimes be displayed if the shift key is pressed.
I have seen the service manual. I checked the signals followed the instruction and found that there was no UART signal from the DSP. I tried to switch on and off many times and there was only one time the display segments were all lit up. More situations were either the shift could light up or the keyboard had no response.
I tried to replace all 4 pcs of SRAM but it did not work.
I suspect the program is corrupted. Did anyone back-up the firmware in EPROMs? I'd like to try it.
My one is an original HP 6812A whose main oscillator is 54MHz.

[heize0]

Finaly it did work. I found two pins of the DSP were short after my re-soldering. Stuppy!
Yet there are some errors related to the DAC12 1A & 1B. But it's better to have a display then I can debug it more directly.