Prepare to qualify (almost)

MrGorf

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After a long battle, I fired up my Pole Position II today. It comes up and plays, but the colors seem to be wrong. The sky is almost white instead of blue, and you cant read the text very well. I have a new vision pro monitor in it that I tested with other boards, so I know it's not the monitor. Any ideas what to look for when I bring out the scope?

Thanks
Don
 

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Update

Before I dragged out the scope, I thought I would clean all of the chips, as whenever I moved the boards around, I would get different problems. I pulled and cleaned all of the chip legs and re-installed them, but still have the same symptoms. I will say the inter-connect board is a piece of crap, as I have to keep re-seating it to get the game to come up. I'm tempted to just get some replacement connectors from Bob Roberts and jumper them together. I'll pull out the scope tonight and check the parts Dick recommended.
 
Update 2

I hooked the boards up on my bench using an arcade shop RGB to NTSC converter and get the same problem, so I know it's not a monitor issue. The car looks OK - nice bright blue on the back, but the sky looks washed out. Also, the track should have the red and white blocks along the edge. The red is there but not the white - however, the text is white. If I go into test mode and display the crosshatch pattern, it is white with a tan background. I don't think that is the correct background color. If one of the PROMS was bad, wouldn't that show up when it checks the RAM and ROMS?

There is an unworking video board on ebay I'm bidding on, so at least I'll have some spare parts to swap. That ends in 4 days, so I guess I have some time to kill.
 
No.

PROMs can only be tested if the memory can be read by the CPU. If the PROM is used to select other chips or to drive the outputs to the monitor (like on Pac Man) then you can't read it by the CPU.

RJ
 
Fixed

Turns out the 74LS174 at location 10C had a bad output, which screwed up the address lines going to the three color PROMS. Replaced the chip and all the colors are correct.

I will be posting the complete restoration pictures once I cut a new back door and button everything up.
 
am i the only one who thought it looked kinda neat with the wrong colors?
 
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