ASO bootleg boot issue.

[Lurch666]

Been trying to fix a bootleg ASO PCB. Like the original SNK PCBs this one is riddles with fujitsus.

Started with a blank screen but after a lot of work I've now got it booting to the CPUB checks which all says OK but it just stops on that screen.

Nothing I've done (checked roms,CPUs,all ram and replaced all faulty fujitus) can get it past this point.

Since there's no schematics for this boardset I'm hoping someone knows something about the boot sequence. Like Ikari it's supposed to do the CPUB check then go straight onto the CPUA check but since it's stopping on the CPUB I'm assuming whatever starts the CPUA check is failing.

Does anyone have any idea which parts of the circuit are checked during the CPUA check so I can narrow down my search?

 

[sukhbir]

Are the program roms being selected I.e C/S on eprom pin.

 

[Lurch666]

Just tried my ikari PCB (which only has two program roms pre CPU where ASO has three) with the second rom for CPUA removed and it still does the CPUA test but gives a rom error.

Will double check the chip selects on my ASO just to make sure though.

 

[Lurch666]

Bit more poking.

Found out that even with CPUA missing it still does the CPUB test.

I had assumed the system would start with CPUA telling CPUB to do it's self test before testing itself but no it appears CPUB is checked then maybe CPUB tells CPUA to do it's self test.

I know from experience of my ikari PCB that other components on other boards can stop the CPUA test from happening.

At one point my ikari was only doing the CPUB test and it turned out to be bad ram on the second PCB. I've socketed all the ram on this ASO but that made no difference.

The interrupt for CPUA appears to be low all the time so I'm looking around that next. It goes to an LS74 that's also connected to CPUB but the '74 check out fine.

I also looked at the eproms for both CPUs and found that are both looping code from 00 to 7F.

On my ikari when it's in demo mode it's also doing the same but jumping to other addresses on the eprom as well.

Have checked the higher address lines but can't see anything holding them low.

 

[Lurch666]

Revisiting this PCB and now it's failing on the CPU B check.
It's saying CPUB ROM0 error and just stops there. Nothing I've tried has changed it.
I checked all the roms again and they are all good,rom select is working.
All the address lines go direct to the CPU and the data lines must be good or the program wouldn't be running.
Checked continuity,swapped CPU,burned another eprom,piggybacked all the fujitsus.

It's annoying because it didn't do this before and I've changed nothing.

Yet it still stops with this error and I've no idea what to check next.