Sega Naomi 2 sudden power off

[MrSandman]

Hi,
I powered up my Naomi Universal together with my Naomi 2 on the weekend. At the beginning, the fan is quite loud but becomes more quiet after a while and then remains nearly silent. After about 30 mins or so, no picture, no sound, no fan noise and it won't power up again immediately when I toggle the main switch, only after some pause.

I did some research and I have come to the hypothesis, that the fan isn't cooling enough and the CPU overheats, as sudden shut-downs are among the symptoms.
Is this reasonable? What else could be the cause? And how should I go about testing?

Thanks in advance for your help.

[thomj]

Have you been running it with the lid on the base? If so what happens if you run it without that on?

[MrSandman]

Thanks for the suggestion. I will try out on the weekend.

[MrSandman]

okay, seems like I have a problem with my GD Rom setup. When before I would sometimes get s communication error, or the boot process would freeze at system initialisation, now the Naomi 2 would not boot or freeze at system initialisation. Will try with my cart again when I have time to see if it is really only the GD Rom setup or something with the mobo.
What a hobby.

[MrSandman]

Tried some combinations to narrow down the possible fault.
I first swapped the Dimm board for my VS3 cartridge to see if I still got stuck at boot. My VS3 cartridge gave me the expected game-not-supported-by-main-board message (Japanese. BIOS, eur. game).
Then I swapped the cartridge for the Dimm board, made sure that the board was seated properly and all components were connected. My combinations I tried were as follows:
When the GD-Rom cover is not closed, I get an error message (as expected).
When the GD-Rom drive is not connected to power, I get an error message (as expected).
When the SCSI cable is not connected, I get an error message (as expected).
Tried the Dimm board test menu, but it timed out (not expected) .

At this stage I suspect that the SCSI cable or the connectors might be at fault or the Dimm board is dead. Or can the Dimm board battery also be the cause?