ANDO AQ6330 repair (optical spectrum analyzer)

[tititoto]

Hi,
we own an old ANDO AQ6330 that most of the time did'nt start up and sometimes startup.
When it does'nt start, even the bios doesn't show up, no beep are heard.
PSU boad was checked and all power rails looks good (I may miss one as I did'nt have a schematic...).
IR camera doesn't reveal a component failure so far.

This device use a EPSON 486-CARD running a windows OS, a kind of old school Raspberry pi!
Bios, PROC, RAM are on board. There is a ISA port, PS/2, MOUSE, VGA, SERIAL, PARALELLE ports.
Here's the manual of this CARD: https://download.epson-europe.com/pub/electronics-de/card-pc/486/486hm-e.pdf

I did following measure:
-check lithium batt: 3V OK
-SCLK:8.XMHz OK (means POWERGOOD)
-SUSSTAT#: 5V
-BATLOW: 5V
-PWRGOOD: 4.8V
-VBK: 5V
-EXTSMI: 5V
-SRBTN: 5V
-RESETDRV:  alternance low/high: cyclic reset of bus.

Any idea to test??

Sincerely,