Congrats CJBob on acquiring both these games and sorting things out. You will gain more comfort and confidence as time goes on and I would highly recommend you "donate" to Clay's to get access to his Pinball Ninja blog website. He just posted his 845th blog repair entry recent which are pretty detailed with pics and usually accompanied by a youtube video too. I think it is $20usd one time and believe me it money well spent as there is lots of things to be learned regarding general pinball repair & troubleshooting and he even teaches you things like how to use a DMM. Here is an example of one of his repair blog entries for a customer's Eight Ball
Bally -17 Eight Ball (repair#825*)
Working on a 1978 Bally Eight Ball today. This is a -17 MPU system, and I’ve worked on this game before. I didn’t remember it, but it had all my trademark repairs. The -17 MPU board was bead blasted to remove corrosion about three years ago (and has held up well.) A coin style cr2032 battery was installed, and a single 2732 EPROM at U2. These are all trademarks of a ninja repair. So what was the problem here then?
The game booted fine. But upon bootup, the standard chime “call to post” song was not heard. Instead the slingshot kickers would fire! Pretty bizarre. (Check out the video of this, hard to explain in words, but once you hear it, you’ll know just what I mean.)
Actually this is a fairly common problem on the -17 and -35 Bally systems. It works like this… the MPU decides it wants to fire a particular coil. It sends the signal to fire (say) coil #7 to the U11 PIA. This peripheral chip then encodes the coil number into 4 bits (1110) and sends this encoded 4-bits of data to the MPU connector J4 pins 1,2,3,4. (Each pin is a bit, either high or low, representing a 1 or 0.)
The encoded signal is sent to the solenoid driver board (SDB) at its connector J4 pins 6,5,4,3. Then these 4-bits (1110) are decoded by the SDB’s 74LS154 chip, and the appropriate TIP102 transistor is pulsed to ground, firing the desired playfield coil #7.
Now if the J4 connector at the MPU board or the SDB has a bad pin, instead of 4 bits, you only get 3 bits (or even 2 bits.) A missing bit is basically a zero, so the data received by the 74LS154 decoding chip is wrong. Hence the wrong coil is fired. So that’s what is happening here. Again, see the video, it really goes through this whole process and how to diagnose which connector is the problem.
Bottom line, when I replaced the MPU board (because of battery corrosion), the female side of the MPU’s J4 connector was not re-pinned. It was fine for 3 years, but now, corrosion on those connector pins have taken their toll. After re-pinning J4 pins 1,2,3,4 (and pin 10, the bank select pin, for good measure), the problem was fixed. So How did I know it was the MPU J4 connector, and not the SDB J4 connector? Well, watch the video!
Note there could have been other issues too. Like PIA U11 on the MPU board could have been at fault. Or the 75LS154 chip on the SDB. But those problems are far less common than failed .100″ Molex connector pins.
Again I refer you to the 7 minute video on this. Much better explanation than the above text and pictures.
Clay's Email is:
cfh@provide.net
http://www.pinrepair.com
