Mortal Kombat Y-Unit - No Video

xodaraP

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Donor 2015
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Hi guys,

I have a MK Y-Unit that isn't producing any video and looking at the reset line of the CPU suggests is in watchdog.

I have looked over the board and found no obvious trace damage, I've verified the ROMs and power is fine as this same setup as run another MK Y-Unit flawlessly. The CPU is getting clock and seems to be trying to boot.

I have noticed that both HSYNC and VSYNC are generated by the CPU and both are completely non existent (floating) - but I'm unsure as to whether this is normal when the board is in watchdog.

I tried replacing the PAL at U42 - pin 12 of this IC connects to the clock pin of U74 as MISC_SEL and then a pin comes from here called WD_CLK (which I assume means watchdog clock, a clock signal designed to let the watchdog know that clock is present?) and I noticed that this pin is not pulsing at all, replacing it with a GAL16V8 I burned did not help so I replaced it with the original PAL

Hoping someone who knows more than me about these might be able to help :)
 
Bump

I've done some searching around and nothing else stands out as being potentially at fault, I am tempted to reflow the U99 since I know this can cause issues, but I don't think that would prevent a picture at startup.

Does anyone know if the TMS34010 CPU will fail to produce a sync signal if watchdog is enabled? Or if there are any circumstances other than a failed CPU where the sync lines would be completely inactive?
 
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