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Sega Outrun Video Fault


Guy

Question

My Sega Outrun has a curious video fault.

Background symbols are displayed incorrectly - i.e. ASCII characters rather than blocks.

Background buildings look very strange - see attached.

 

When I run a memory test, IC65 fails.

I've replaced IC65, but the fault persists.

I suspect that it's either an address or data bus fault, rather than the RAM itself.

Time to get the scope out if I can figure out how to physically get to the bus - the video board is the bottom board in the stack.

 

If anyone else has come across this please let me know.

 

Regards.

background.JPG

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Hard to tell from that photo but I suspect it isn't the background at fault, as that isn't built of letter sized blocks, faults there usually are much larger (tiles), you probably have a character (i.e. text overlay) plane fault. Plus the gfx ROMs wouldn't have a character set in them, but the character plane would.

 

How sure are you that you didn't cause any damage to the track and plate through holes when you replaced that RAM, you could now have a working RAM chip that is not correctly wired up.

 

To work on the back board you just work on it in mirror image, you can get one of the high res photos of the board and flip it on the X axis, then you can overlay the solder side image and use that as a map. Or just reverse the chip pinouts in your head.

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Hi Womble,

 

Thanks very much for coming back to me.

We have a Pace SMT rework station at work so I was able to remove the RAM without too much damage.

I then double checked under a microscope and fixed any issues that were apparent.

 

I also buzzed every pin on the device to make sure it was connected to bus / control line.

 

Also the fault symptom and IC Failure code did not change when I swapped the RAM.

 

You are right about flipping the board over - the looms are just long enough.

Tonight I'll check each bus line with a scope to see if I can find the culprit.

 

Regards,

- Guy.

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