Centipede High Score Resetting

[jasonsmith]

I need your help again fellas.

Anyone with a Centipede or variant knows that the high score can be reset while in the test mode and while pressing all 3 buttons (p1, p2 and fire). For some reason my Centipede is stuck in this reset mode. Here's what I know.

- It will let you log your high scores.
- If the game is turned off the score revert back to factory defaults.
- If I enter test mode the scores are instantly reset going back to factory defaults.
- The "4 FF" is always displayed on the test mode screen, which should only appear after all 3 buttons have been pressed and the score is wiped.

Rather than throw parts at it I thought I would seek some help.



https://dl.dropboxusercontent.com/u/85675826/Screenshot%20from%202014-04-16%2009%3A15%3A51.jpg

[lordkahless214]

Sounds like it could be the 555 timer. I Found this page on KLOV, sounds like the same issue you have, has a couple of other fixes you can try

http://forums.arcade-museum.com/showthread.php?t=42462

[jasonsmith]

Awesome man, thanks for the link. I had a strange ceramic cap attached to the triple 5 so it could totally be possible. Thankfully I have all the parts, will give it a go in the morning.

[jasonsmith]

Well swapped out the 555 timer and the cap (C84) no change

Maybe it's actually the EAROM, I dunno. This is above my pay grade so I think it may be time to just start throwing parts at it.

[John's Arcade]

Well swapped out the 555 timer and the cap (C84) no change

Maybe it's actually the EAROM, I dunno. This is above my pay grade so I think it may be time to just start throwing parts at it.

that NVRAM could be bad.

[jasonsmith]

I just noticed that I have a NI NC7055 chip installed in that spot. As per JROK's website that could be a replacement?? Idunno but maybe that's the issue? Nothing in my manual or schematics shows that p/n.

[lordkahless214]

Well the NI7055 was sometimes used from the factory in place of the ER2055, which was the more common EAROM, I believe that my Millipede also has a NI7055 in it.
If your voltages all check out, and you have tried resetting your high scores after you replaced the 555, the next thing I would do is like John suggested and replace the NVRAM/EAROM chip.
For that you have a couple of choices, you can replace the EAROM with a direct replacement,Mike's Arcade has those http://www.mikesarcade.com/cgi-bin/store.pl (just look up earom), or you can order one of JROK's adapter with a more modern EEPROM http://www.jrok.com/hardware/earom/ . If it were me I would probably go with the JROK board because it's about the same price, doesn't need the odd voltages and is probably more reliable.

[jasonsmith]

If the jrok board will work on a stock setup I'll probably go with that. Arcade chips seems to have the stock ER2055’s in stock as well for only 4 bucks. I wish I had one just to test in case its not the ram.

[lordkahless214]

I think it does work on stock, but I would drop Jrok an email and ask to be sure, but maybe someone who lives close could let you borrow a EAROM to test in your game?

[jasonsmith]

I'm at the beginning of my arcade hobby so I may as well just suck it up and get a few to keep on hand.

When I swapped out the cap I checked it and it was still quite healthy. Not really thinking it could be any of the IC's in the high score circuit but you never know I guess.

[jasonsmith]

Well I got my ER2055 in the mail today, swapped it out and sadly that didn't fix this issue. There's something else going on, have no idea what right now. Man this Centipede is testing my patience.

[jasonsmith]

I fired up an old thread on KLOV and got my high score issue fixed. It ended up being VR1 outputting a positive voltage when it should have been a negative.

If anyone has this issue test all the voltage test points, if you have +15v at the -15 test point just change out VR1 (7915).