MV1A Problem

My MV1A, the board a usually use just died on me. It started to show some problems a few weeks ago (taking too much time to start while making some clicking noises in the process).

Now, it simply boots to a garbage screen with a few colors making the clicking noise, so i assume it's in watchdog.

I've read a few repair logs but i'm not sure what readings i should find on the ram pins (i guess this is a starting point), that's why i'm calling for help.

I checked these pins with the following result:

Ram 1
Pin22 - Hi/Lo changing
Pin27 - Hi

Ram2
Pin22 - Hi/Lo changing
Pin27 - Hi

Ram 3
Pin22 - Hi
Pin27 - Hi


Ram 4
Pin22 - Hi
Pin27 - Hi

What should i be looking for?

Thanks in advance.

That sounds like watchdog. 27 on RAM1/2/3/4 should pulse too or the RAM is never going to be written. RAM1/2 (WRAM) is the main concern since 68k is going to crash quickly without writable WRAM on stock BIOS. Pin 22 pulsing is good since it implies 68k probably isn't dead.

MV1A uses the NeoCD chipset so I'm not 100% sure about the pinouts on a cart system. The wiki has pinouts here that covers most of the 68k traces. Check against a 68k pinout that A23~A17, AS, LDS, UDS, R/W, D0~D15 are good. The address and purple labelled pins (which should be pulsing) are the main concerns. Pin 27 on RAM1/2 probably lead to somewhere on the MGA or possibly the PALs on the far left of the board. The pinouts floating around for the BIOS/WRAM/68k connections are also useful to check.

If you have an EPROM burner and a 27c1024 you can burn the sp1.bin with a diagnostic ROM and see if that gets past watchdog and displays any error info. It might or might not depending or where the exact fault is.

Thank you for your input.

I do have an eprom burner, and i've burned more than one Unibios before, but every time i tried to burn a diagnostic ROM in the past i got stuck with an error, can't understand why.

Another to thing to check is the BIOS /OE pin which I'm 99% sure also leads to NEO-MGA. Apart from that, the pinouts posted in other threads for systems that use NEO-C1 chips instead are mostly usable but the NEO-C1 connections should lead to somewhere on the MGA instead. RAM1/2 and BIOS address + data connections would be the main things I'd check for first out of those.

_rm_ said:

Thank you for your input.

I do have an eprom burner, and i've burned more than one Unibios before, but every time i tried to burn a diagnostic ROM in the past i got stuck with an error, can't understand why.

Click to expand...

Did the EPROM not verify correctly for some reason or did something else happen? I haven't seen any weird issues on my collection of MVS/AES systems as of a few versions ago.

smkdan said:

Did the EPROM not verify correctly for some reason or did something else happen? I haven't seen any weird issues on my collection of MVS/AES systems as of a few versions ago.

Click to expand...

If i remember correctly, it gives an error right at start. I will try to burn again soon.

_rm_ said:

If i remember correctly, it gives an error right at start. I will try to burn again soon.

Click to expand...

The file will never do that. It's either the chip, the burner or the pc.

Hi There,

my MV-1A has failed in a similar way. I wanted to consolize the PCB, so after messing around with the controls while being in Service Mode (DIP1 on), i restarted it and it died. It shows a flashing screen with random symbols and coloured blocks and I'm hearing the click of death from the speakers. I already replaced the BIOS with a Unibios, replaced the 68k and removed the battery. Still stuck in watchdog.
I don't see broken traces and I doubt there are any, because it worked just a few seconds before restarting it, so I suspect turning it off and on has zapped one or more chips. Voltages are fine, I'm reading 5,01V directly on the Jamma connector. Bridging the BERR and watchdog jumpers leads to a solid blue or white screen with flickering red pixels a few seconds after turning on the power. These pixels also appear in some of the flashing blocks in watchdog mode and when touching the Bios chip.

Any suggestions?
Thanks!