Sprint 2 troubleshooting

weirdal1968

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A friend said it was probably something easy. Yeah I've heard that more times than I care to remember...

When you turn it on, the game boots up and you can see the cars zipping along the track without a care in the world for a few seconds. Then I hear a screech-ish noise and the bottom 2/3rds of the screen suddenly fills with the letter A or the letter B and the game locks up. Switching to the self test mode doesn't give any useful info aside from one letter in the mess of As and Bs counting up from A to G and sometimes E7 appears in the lower left corner. The self test doesn't display anything like what is described in the manual. Sometimes it displays 2/3rds of the screen full of the character G that slowly works down to the lower right corner but it never fails in the same spot twice. The top line of text often turns to garbage. I'll try and take a picture next time I'm there.

Replaced the two 16v 8000uf caps (leaking fluid!) and the LM323 regulator with one from my Night Driver PCB. The 5v line had been hovering around 4.89v but is now a rock solid 5.03v. Unfortunately the power supply repair has not fixed the problem.

Cleaned the pins on the 6502 but that didn't fix it. Obviously the CPU is running fine for a few seconds before it faceplants. The display looks fine as far as sync or text so it probably isn't in the display circuitry.
 
There are mainly two reasons when my Sprint2 isn't running properly.
The first one is that one the coin switches is stuck, so I have to move it back to a neutral position again.
The other seems to be corroding connectors. So I wiggle the main board connector a little bit and it runs fine for a while again.

Maybe not the problem for you at this point, but the coin switch issue is pretty common I heard, so it might be good to remember.
 
This problem is a weird one. The connector looks a little fugly - its the cheap kind with the push-through pin fingers and a few look funky. Figured if the power supply was good, it would at least run and have good video. The NC coin switch bug apparently says otherwise.

I'll test the CPU in another game just to rule it out - not that it was really a suspect - and then hardwire the coin switches closed to see if it runs reliably.
 
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