Karate Champ scrambled image

tandrews_ny

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I have a Karate Champ with a scrambled image when it boots. It's not the monitor but appears to be the PCB. I have verified all eproms as working with my writer. I have attached a picture of the issue.

This scrambled image does move but no activity from the game can be seen (coining, etc).
 

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I have a Karate Champ with a scrambled image when it boots. It's not the monitor but appears to be the PCB. I have verified all eproms as working with my writer. I have attached a picture of the issue.

This scrambled image does move but no activity from the game can be seen (coining, etc).

Did you check the voltages at the PCB? Start there. If you're not getting a good +5VDC then checking anything else will be a waste of time.
 
Getting 5vdc bang on.

Next steps I would take are:

1) Check for a Clock Signal.

2) If you do, then check to see if the reset on the CPU is pulsing.

3) Check the Address Lines and the Data Lines on the CPU for activity.

If you have all of those, then check the ROM's. Check the Chip Select lines, and the Address/Data Lines on the ROMS.
 
If you own a logic probe then follow Arcadenut's suggestion to check reset line on cpu which should be high then interupt lines, address and data lines. It's likely to be a TTL close to the cpu with floating or bad outputs.
 
If you own a logic probe then follow Arcadenut's suggestion to check reset line on cpu which should be high then interupt lines, address and data lines. It's likely to be a TTL close to the cpu with floating or bad outputs.

Sadly I don't and I figured it is probably a TTL issue. I do own a Oscope though, so I'll need to put this on a bench and measure it.
Anyone got some useful guides?

do you do repairs Arcadenut? if so, how much? I have a commando doing the exact same thing so i need to investigate that too. I'd love to fix this myself, but time is precious and we have many other games we're looking at. I also don't have a workbench to test this on as it's not JAMMA.
 
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Sadly I don't and I figured it is probably a TTL issue. I do own a Oscope though, so I'll need to put this on a bench and measure it.
Anyone got some useful guides?

do you do repairs Arcadenut? if so, how much? I have a commando doing the exact same thing so i need to investigate that too. I'd love to fix this myself, but time is precious and we have many other games we're looking at. I also don't have a workbench to test this on as it's not JAMMA.

Sorry I do not. There are several really good people on here who might though. There should be a thread (might even be a sticky thread) on who fixes what.
 
...because maybe this board is magical and can have perfect sync on the monitor but no clocks!.

Here's a learning opportunity for you Mark, it's not magic as the CPU clock on that board is additionally buffered from the video counters. So it's possible to have perfect video sync AND have no clock to the CPU.

That's not even magic !

It's also often a very good idea to check a CPU isn't stuck in reset.

Weak trolling man, you need to work at it.
 
Here's a learning opportunity for you Mark, it's not magic as the CPU clock on that board is additionally buffered from the video counters. So it's possible to have perfect video sync AND have no clock to the CPU.

...and inverters are *such* a common failure...
 
What weird trolling.. on KC the cpu clock comes from the other board in the stack - so as well as potential for TTL failures, it could also be the interconnect. So checking CPU clock is very much one of the first steps you should do regardless if the video clocks are working.
 
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