No Cross Hatch and Address Error

[adrianomartins]

Hi,
I have a MVS 4-slot board with UniBIOS 4 and "interesting" behaviour.
When I switch on without a cartridge, no cross hatch appears, but the below error message. Sometimes the picture flickers white 1-2 times and then the below error message appears.
When I insert a cartridge, the game starts normally without errors.
If I go to the test menu while the game is running, the cross hatch appears (without errors).
Battery replaced, voltages correct, cartridge contacts clean.
What does the error message mean or what could be the reason for the cross match not appearing without a cartridge?
Thanks in advance.

 

[Azathoth]

Do you get the same results using a stock bios?

 

[Neo Alec]

Or what do you get with the diagbios?

I wonder if you've got some bad traces on the cart slot or somewhere along the route from the cart, since it seems to be acting like there's a cart inserted when there isn't one. Not sure how much help the diagbios will provide there, but it would be good to check to cover all bases.

 

[city41]

I think this could happen without a cart too if the bios is faulty. When a Neo boots, first the bios runs some startup code. If that code is corrupted, it could cause the cpu to jump to a totally random place and get an address error like this. This is the unibios's address error handler, so that part of the bios seems to be intact at least.

When I insert a cartridge, the game starts normally without errors.

That could mean the bios is corrupted when it runs its "oh, no cart is inserted, show a diagnostic screen instead" code. By having a cart in, the bios won't take this path and the path for booting up a cart might not be corrupted and thus works fine.

All wild guesses. I'm much more of a software person than hardware.

I think swapping in another bios and seeing if the error goes away would be a good test to try.