Just acquired my first System 80 game! It's a decent-shape Bone Busters that was rather dirty and mostly working, although having been through some battery damage that's been neutralized and cleaned.

I tore apart the playfield to clean it, change the GI lights and such and and am having some behavior that I didn't expect to see upon a game start. I'll link to the youtube video to show you what's going on.

YouTube Video:

Observations:
1. ) With or without balls in the trough, the same thing happens. The left outlane coil fires over and over, searching for a ball it seems.

2.) The bigger issue, which I think is what I should be chasing, is that the Switch Tests show nearly all switches CLOSED. There's at least twenty of them.

3.) Credits seem to increase by 2 when I click the coin chute lever. This can be seen in the video. Odd. DIP settings are 00 00 00 C0.

4.) From what I can tell without the manual as reference, all solenoids fire when tested.

5.) New RIOT chip. New ROMs.. some replacement ICs on the main board.

6.) No flippers work at all during the game. Slam switch is open (as required on this board). Tilts and slam switches DO work as intended.

I have a manual on order that will be here Thursday. Until then, I can't locate too many schematics to help me understand the board layout.

Questions:
a.) What connectors on the boards control the switches? Is it A1-J6? I've reseated it and cleaned the contacts as best as I could but there's no change in behavior.

b.) How on earth do you test a single switch in the switch test mode? I can't seem to figure that one out. Driving me bonkers!

Any place to start would be great! And don't tell me "ground mod" because I already know I'm just waiting on the manual to arrive before doing any major work on it.

All of the ones I tested with a multimeter trigger fine (ball trough, launch lane, left outlane). I don't know the corresponding numbers on the matrix though to know which switches are being deemed 'closed' so I can't say for sure which it's whining about.

I think you're right. However, it's not physically closed which is why I'm baffled. The manual will be delivered today if the USPS tracking is correct. I'll see what it leads me to.

Switches closed are the following, suspiciously the first four columns of the switch matrix:
#1-3
#10-13
#20-23
#30-33
#40-43
#50-53
#60-63
#70-73

Switches 60-73 aren't even used, leading me to think there's something else going on than bad switches.

Switches in columns 4,5, and 6 seem to operate fine.

I got the manual and am attempting to trace the matrix to its components but I'm still rather new at it. I don't know whether this means a strobe is at fault or a return, or one of the chips that processes either.

Any thoughts that stick out at you? Chips U4, Z14, Z13, and Z11 have all been replaced by the previous owner. All edge connectors appear clean and trace well on the DMM.

After some diagram reading tonight, I had the thought that Z13 (which handles the return lines 0-3) may be bad causing all row returns to go low and trigger as closed (00, 10, 20 ... 70), (01, 11 21 ... 71) ... (03, 13, 23 ... 73).

Since the switches on (04, 14, 24 ... 74) through (07, 17, 27 ... 77) were operating fine and showing proper behavior in the test #18, I figured that I could swap Z13 with Z14, both 7400 chips.

When I did that, upon turning on the game, I get TILT SWITCH CLOSED over and over and over, unable to progress past that point. TILT switch is SW 57 (return line 7 on Z14) which was operating just fine before now shows a failure.

Am I right in assuming that the 7400 chip in Z13 originally is bad? If the problem seemed to migrate to the new return lines, doesn't that signify that something's amok with that chip?

(Also found that diode 6 on 2A17P2 is bad. Right lower flipper. All other diodes seem to pass the test.)

Just an update on the thread in case future me is reading this. Replaced the 7400's and got no change in behavior. Ordered Z15's 7432 and socket to see if this is the issue. Logic probe shows 2 high's into the 7432 OR gate outputting a LOW. Something tells me that ain't right.

Another update for my future self - replaced the Z15 7432 and socketed it and the game works! I now get one credit per coin switch trigger instead of 2 or 4, the game starts fine, tracks the balls properly too. No crazy firing of the solenoids.

Now onto fixing flippers, switches, lamps that are out etc. Woohoo!