Naomi 2 -15/31khz signal weird issue

[ravepants]

Hi All,

I have a Naomi 2 that was recently recapped it was working fine up until recently when it started booting to a black screen (with a cart or NetDimm/Pi)

I read in one of Tylers posts on AP that it could possibly be a corrupt BIOS, so I got a new one (The New 2020 version patched for Atomiswave) and i still got the black screen.

I did the usual voltage tests (all spot on) re-seated the bios chip, made sure the on board battery is still good but still nothing.
in a fit of desperation i tried flipping the 15k/31k switch on the filter board to 15k, and when i booted up it sprang into life!
To test it i booted it again in 15k and it still worked, then i flipped it back to 31k and rebooted and it came to life again in 31k.

This seems to be intermittent though, as i left it on to soak test for about 2/3 hours in 31k and when i returned to it I had a black screen again, but when i flipped it back to 15k and soak tested it was still on about 2/3 hours later.

Any one have any idea where i can even begin to look at what might be causing this?
My instinct says maybe the video encoder or whatever part of the circuit deals with the 15/31k switch, maybe one of the GPU's? i'm stumped!