Weird video issue on JAMMA PCB (update: suicided game?)

PCB problems and fixes
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Sumez
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Weird video issue on JAMMA PCB (update: suicided game?)

Post by Sumez »

I recently bought this game on eBay - I still have the time to file for a refund, but if possible I'd prefer to just solve the issue. So I'm hoping someone here has seen something similar and have a suggestion.

The game in question is the relatively obscure Alligator Hunt, and the issue is best demonstrated by a video:


It seems like action on the screen (in particular moving sprites??) causes the horizontal orientation of the picture to semi-randomly offset. This looks like the kind of issue you'd occasionally see on a monitor, but it's definitely an error on the PCB, and I've tested it on both a New Astro City cab as well as a supergun connected to a Sony PVM, and both see the same thing happening (it moves around a bit more on the NAC which I assume is due to some kind of stabilizing function on the PVM)

Any suggestions?
Last edited by Sumez on October 29th, 2018, 2:02 pm, edited 2 times in total.
Sumez
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Re: Weird video (hsync?) issue on JAMMA PCB

Post by Sumez »

Wow, for some reason my Google skills missed this post from another forum: http://www.ukvac.com/forum/alligator-hu ... 65319.html

It seems that it's a suicide battery issue, and can be fixed by switching out two ROMs on the board. The thread is inconclusive about wether this was actually the issue though.

So if anyone has experience with this issue, maybe via any of Gaelco's other games, I'd love to hear people's experiences.
Last edited by Sumez on October 29th, 2018, 2:04 pm, edited 1 time in total.
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yosai
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by yosai »

Is video ground connected?
Sumez
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by Sumez »

yosai wrote:
October 29th, 2018, 2:04 pm
Is video ground connected?
Good suggestion that I somehow didn't think of. I recall my TGM2 board requires video ground, but it might be connected to the common ground rather than video ground. I'll measure and check back later today.

Where is video ground supposed to go on a NAC chassis?
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yosai
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by yosai »

Get a piece of wire and carefully connect the video ground to ground and the issue should resolve.

If that works you could make a JAMMA pass through with the grounds connected.
Sumez
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by Sumez »

Already using a jamma passthrough for a bunch of these purposes (such as measuring voltage, capture breakout and a negatron for -5V)

If just connecting video ground to common fixes the problem, that's cool. But couldn't the issue be caused by the cab sharing those two in the first place?
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by Sumez »

Alright, connecting video ground to ground didn't change anything at all.
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nem
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Re: Weird video (hsync?) issue on JAMMA PCB

Post by nem »

Sumez wrote:
October 29th, 2018, 2:01 pm
It seems that it's a suicide battery issue, and can be fixed by switching out two ROMs on the board. The thread is inconclusive about wether this was actually the issue though.
Sounds weird, but it is very explicitly stated on the Dead Battery Society site. I would definitely try it.
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Re: Weird video issue on JAMMA PCB (update: suicided game?)

Post by yosai »

If you can change the ROMs its definitely with a try. If that fails, check the traces on the board around the video circuitry and the video ground.
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