seanriddle
Member
I picked up a JP in pretty good shape, other than being very dirty. I've been working on getting the electronics working- resoldering a few broken wires, replacing a bad diode and a bad transistor, etc. I noticed the coil for the diverter wasn't installed and the associated flashers weren't working.
I assumed Q41 on the CPU board was bad, but I installed the coil first. When I turned on the game, the diverter coil stayed on during diagnostics, so I checked D14 on the PPB board and it was shorted. I didn't have a spare on hand but I clipped the diode. Next time I turned on the power, there was a loud buzz; so I shut it off quickly.
After a few more short power ups, I noticed that several coils were immediately coming on and staying on- all of the coils numbered 1-8: diverter, knocker, ball release, auto launch, etc. I pulled connector CN11 from the CPU board so I could power up for testing without burning the coils up.
These coils aren't driven by a PIA; there is a latch on the data bus that goes to 2 AND gates for blanking, then to 2N4401 driver transistors then to TIP122 transistors.
I used a logic probe to look at the AND gates, and they are being driven correctly, but the outputs are bad. I clipped the one at 3J and the signals didn't change, so I'm guessing that means I blew my 2N4401 driver transistors, and likely the TIP122s.
I can replace all that, but I'm trying to figure out what I did wrong. Was this caused by powering on the machine with D14 on the PPB board clipped? I don't see how that could be the case, but that's the last thing I did before this happened.
Afterwards I measured voltage on the PPB board, and J6-6 is about 43V. I hadn't measured this before, so I don't know what it was before all this happened, but the PPB schematics say +28V; however, the coil wiring diagrams on pages 31 and 38 say 32V and the P/S schematic on page 57 says 34V. This comes from BR2 on page 47, which is fed with 25VAC, so 34VDC seems correct.
Maybe there's a short between 34V and 50V on the PPB board and the 15G470KM on the P/S board is holding the 34V line to 43V?
Thanks for any ideas.
Sean
I assumed Q41 on the CPU board was bad, but I installed the coil first. When I turned on the game, the diverter coil stayed on during diagnostics, so I checked D14 on the PPB board and it was shorted. I didn't have a spare on hand but I clipped the diode. Next time I turned on the power, there was a loud buzz; so I shut it off quickly.
After a few more short power ups, I noticed that several coils were immediately coming on and staying on- all of the coils numbered 1-8: diverter, knocker, ball release, auto launch, etc. I pulled connector CN11 from the CPU board so I could power up for testing without burning the coils up.
These coils aren't driven by a PIA; there is a latch on the data bus that goes to 2 AND gates for blanking, then to 2N4401 driver transistors then to TIP122 transistors.
I used a logic probe to look at the AND gates, and they are being driven correctly, but the outputs are bad. I clipped the one at 3J and the signals didn't change, so I'm guessing that means I blew my 2N4401 driver transistors, and likely the TIP122s.
I can replace all that, but I'm trying to figure out what I did wrong. Was this caused by powering on the machine with D14 on the PPB board clipped? I don't see how that could be the case, but that's the last thing I did before this happened.
Afterwards I measured voltage on the PPB board, and J6-6 is about 43V. I hadn't measured this before, so I don't know what it was before all this happened, but the PPB schematics say +28V; however, the coil wiring diagrams on pages 31 and 38 say 32V and the P/S schematic on page 57 says 34V. This comes from BR2 on page 47, which is fed with 25VAC, so 34VDC seems correct.
Maybe there's a short between 34V and 50V on the PPB board and the 15G470KM on the P/S board is holding the 34V line to 43V?
Thanks for any ideas.
Sean