MV1AX MVS motherboard with watchdog click of death

[BILLSLEY]

Hi all, I have a MV1ax motherboard that has the watchdog click of death, this has come directly from a arcade breakers and looks like its in relitivly good condition (bought as a job lot). This board has no discernable corrosion or broken traces. But it does have a lot of the small smd capacitors missing on the rear of the board. PC9, PC11, PC13, PC14, PC22 and PC33. would this cause the watchdog as I have another MV1C that also has 3 missing PC capacitors and that works fine? also what value of the said capacitors or am i looking in the wrong place.
What would I start with as diagnostics for this board? im just a begginer and bought 3 boards, one that worked and two broken ones so I could learn, one of the orther broken ones I got to work, so im looking for help for this next one.
Thanks guys

 

[Ryoandr]

Capacitors labelled PC are Power Capacitors, 100nF ceramic. They are typically used near every IC to filter their switching noise. However they are not critical.

Watchdog loop is CPU not getting program to execute right in one way or another basically (please all experts here correct me if I'm wrong :p ). I can be, among other things :
dead bios
faulty address / data traces to the bios
faulty chip corrupting these address / data lines.

MV1A has several NEO-BUF connected to the 68k in one way or another and these love to fail. SNK1A/B PALs can also fail.

Start with the first 2 possible causes, but also keep in mind you might be in for a lot of NEO-BUF changing (if you even have working spares or clones).

 

[ragefan]

Hi,

I would suggest the following :
- check continuity between 68k, sp1 rom and ram 1/2.
- if ok, change bios with diag bios
- check ram 1/2 with a Logic analyser to see Bad behaviour on WE, CS pins.

If all ok, likely disable the Watchdog by shorting jp2 to see other pin status.

Then, would check neo-buf and continuity between neo-mga and 68k.

Happy to help