Neo Geo MVS - Z80 Error

Sorry, I'm losing track of you here.

From what I have read, if I just replace the bios with the diagnostic bios I can test the main MVS board apart from the Z80 if I have no cart inserted. But if I want to test the Z80 chip then I need a CHA board from an old game with an eeprom on it that has the second part of the disgnostic bios on it, not a standard game board.

 

I don't know about that test bios, was just basing on what I know of the Neo Geo system. You don't need that test bios at all. It's almost certain you have a corroded/broken trace or a faulty sound CPU, because that's what breaks 90% of the time. The REAL way you save yourself hassle with that is pop that Z80 out and test it on any known good Z80 based device or system. for example you could use a Master System machine as test for your Z80 chip.

Edit: is something else is broken or blown and it's holding the bus down or you have a broken trace, that Z80 test on the test bios will not help you at all as it will be unable to start, by itself.

Same as what happens with the SNK own Z80 test ROM (SM1).

 

You change the BIOS in the system to run the diagnostics. However, if you actually want to know WHAT the "Z80 error" is (the built-in diagnostic is bloody useless in that respect), you have to sacrifice a cart to build a diagnostic cart.

You put a second chip in the CHA board programmed with m1.bin, leaving the S1 ROM on the board. You can leave the PROG board in there, but try fitting it all back into the cart if it's socketed! There's no need for the PROG board, hence you can take it out. And don't forget to hold down the relevant button when you power up!

 

Ah right,

I've been testing the traces from the Z80 to the other chips, I've managed to confirm that half of them are working, however it's a long process since I have to manually follow the trace across the board until I find where it's meant to go. Is there a technical document anywhere that you know of please that will tell me where each pin is meant to go? I haven't managed to find anything through google.

Thanks for the advice

 

I imagine the author of the diagnostic bios didnt want people to have to spider wire in a replacement SM1 chip on systems that use a SMD chip there. Carts is DIP - easy to fit a socket and update/replace.

 

Actually the last gen chipset (that tiny board with upright cart slot) has no means of testing the sound hardware (no SM1, no Z80 handshake test). Which is probably why he developed that method of testing.

 

The MV1AX has a small SOP chip for the SM1 too. Which there is no direct programmable replacement.

 

MV-1C was the one I was talking about. It has a sort of a "cosmetic issue" with UNIVERSE BIOS because of that. It's own original BIOS (a revised BIOS specific for it) doesn't perform Z80 tests at all. There's no "loose Z80 chip" on that board as it's integrated inside the "NEO-YSA" chip along with the Jamma I/O stuff, FM synth and assorted/related stuff.