6820 vrs 6821

firepowerplayer

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I am working on a -17 bally mpu. When I went to reseat the socketed chips I broke a leg on the 6820 chip at U11. I used a 6821, but the board just keeps on flashing. Do I need a 6820, or is it another problem?
 
For all intents and purposes, 6820 and 6821 are fully interchangeable, so that's not an issue.

Please describe the flash sequence you are witnessing at powerup, I can't tell you anything more just from "keeps on flashing".

Chris
 
For all intents and purposes, 6820 and 6821 are fully interchangeable, so that's not an issue.

Please describe the flash sequence you are witnessing at powerup, I can't tell you anything more just from "keeps on flashing".

Chris

Could be those pesky scanbe sockets in there.
 
I made like the VA and put a fake leg on the 6820 and it started working. When I went to the guys house to install it ( guy is a friend, Would not do that normally) His dog jumped up and the board hit the coffe table. It smashed VR1 in the valid power circuit under standard stewart operating procedure.. I replaced it but still no 4.8v at u9 pin 40. That really sucks.
 
I made like the VA and put a fake leg on the 6820 and it started working. When I went to the guys house to install it ( guy is a friend, Would not do that normally) His dog jumped up and the board hit the coffe table. It smashed VR1 in the valid power circuit under standard stewart operating procedure.. I replaced it but still no 4.8v at u9 pin 40. That really sucks.

U9 pin 40 is the reset pin. It should go low briefly then high, though I'm sure you know that.

I would put a DS1811 in the reset circuit. Then you'll have one less thing to worry about.

If you're working on a -17 the best thing you can do is start from scratch with a test ROM and just the CPU. Then build out from there. You're probably looking at replacing the ROM sockets at a minimum.

Personally I would probably convert it to a single 2764 but that might be difficult if you don't have access to an EPROM programmer:
http://warpzonearcade.com/?p=580
 
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