(Topic ID: 321894)

Solenoid Transistor and Fuse Blowing - Baby Pac-Man

By zeldarioid

1 year ago


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#1 1 year ago

Hi! Hoping to get some help figuring out an issue I'm experiencing with my Baby Pac-Man.

When I bought the game, it had some intermittent issues where occasionally, it wouldn't kick the ball out of the trough when you got to the pinball portion. At the time, I repinned some connectors, and got it back to working reliably for a month or two. Recently, however, there is no intermittent nature about it: The solenoids do not work at all. Putting the game into test mode, only the flippers will fire during the solenoid test. I repinned J6 on the driver board, and as far as I can tell, all the voltages coming through at the various test points on the driver board are what they should be, and the VCC pin from U4 has 5 volts...but the Q36 transistor and the solenoid 1A SB fuse below the playfield both get destroyed immediately, so clearly something is failing or shorted somewhere, but I'm not sure how to figure out what is going on.

I'm new to this stuff, and don't quite understand how to follow the schematics with confidence, but it looks like the Q36 transistor has to do with the drop target reset. I have also tried checking the coils and I think those are all reading as fine via DMM, the various resistors and diodes in the Q36 circuit seem fine on the board, I don't see any obvious shorts w/ wires hanging down anywhere or anything...I could definitely use some help in where and how to next look for a problem to narrow this down! I feel like it should be something obvious w/ the transistor getting killed and the fuse blowing, but as I said, I'm new, so

One thing I've wondered about, since the transistor seems to relate to the drop target reset, is maybe looking at the diode on the big coil next to the drop target bank, but it's facing the playfield so it isn't easily accessible w/o removing the coil, and I just haven't done that yet. Would that be anything that could cause this issue? Are there other things I can check under the PF while the game is in test mode maybe? I have also checked voltages at the fuse holder where the 1A SB gets popped, and I've got ~44V on the one side, and ~3V on the other (w/ no fuse in place), so I'm also a little surprised to see the fuse burst there unless maybe a coil is trying to fire during gameplay/during test mode and that firing causes a spike in the voltage? I’ve also confirmed there are no switches stuck closed.

Please help!

#3 1 year ago

If the diode is bad or broken on the coil that Q36 drives it will blow the transistor immediately. I would disconnect the small wire from the coil and cut off the blown transistor see if the fuse stops blowing and the other coils work

#4 1 year ago
Quoted from KJL:

If the diode is bad or broken on the coil that Q36 drives it will blow the transistor immediately. I would disconnect the small wire from the coil and cut off the blown transistor see if the fuse stops blowing and the other coils work

Thank you for the reply! When you say to disconnect the “small wire” from the coil, which do you mean?

#5 1 year ago

you can remove either wire from the coil to break the circuit.

#6 1 year ago

Rickoshay is right. If there is only 1 wire to each lug it doesn’t matter. If there are 2 to a lug that is the power(big) wire usually and the single wire is the little drive wire which The relevant transistor is connecting to ground. I always disconnect the small/drive/wire connected to the transistor as there is only 1 to solder back.

If you can test continuity between each lug of the coil and the metal tab of the
Blown transistor you will know which is the drive wire. The others wire should have the banded side of the diode if you replace it

#7 1 year ago
Quoted from KJL:

Rickoshay is right. If there is only 1 wire to each lug it doesn’t matter. If there are 2 to a lug that is the power(big) wire usually and the single wire is the little drive wire which The relevant transistor is connecting to ground. I always disconnect the small/drive/wire connected to the transistor as there is only 1 to solder back.
If you can test continuity between each lug of the coil and the metal tab of the
Blown transistor you will know which is the drive wire. The others wire should have the banded side of the diode if you replace it

Based on your suggestion, i snipped the single wire, and then figured i might as well investigate the coil visually inside while I was at it, and lo and behold, I’m thinkin the coil is toast. There is a sizable bulging inside the coil sleeve, and I can’t (obviously) remove the sleeve at all. I’d love to understand the *why*, so I don’t replace the coil (and diode) and have it just happen again, but maybe it’s something as simple as time + use/heat = failure?

Either way, I’m going to order a replacement coil and diode, and see what happens, but otherwise, with having that drop bank reset coil snipped out of the circuit, the rest of the solenoids work and the game can be played! Thank you guys for your help, and hopefully I’ll have a complete win to report with the new coil when I get it in and installed

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#8 1 year ago

Yep, that's knackered!

Make 100% sure you install the new coil/diode with the banded end of the diode facing the supply side wire.

Don't assume the new coil will have the diode oriented in the same direction as the old coil.

#9 1 year ago
Quoted from pins4u:

Yep, that's knackered!
Make 100% sure you install the new coil/diode with the banded end of the diode facing the supply side wire.
Don't assume the new coil will have the diode oriented in the same direction as the old coil.

Thanks for the tip! So just make sure that, if I lie the coils with the lugs pointing up, the diode is oriented the same way on both the old and new coil, and then obviously solder the wires to the matching lug on the new coil from the old one - the coil itself (which I just ordered) is a direct replacement part from Marco Specialties, so should otherwise be good to go - just have to make sure the diode is facing the same way, and that I wire it up the same way?

#10 1 year ago
Quoted from zeldarioid:

Thanks for the tip! So just make sure that, if I lie the coils with the lugs pointing up, the diode is oriented the same way on both the old and new coil, and then obviously solder the wires to the matching lug on the new coil from the old one - the coil itself (which I just ordered) is a direct replacement part from Marco Specialties, so should otherwise be good to go - just have to make sure the diode is facing the same way, and that I wire it up the same way?

Correct assumption - and if the diode ends up facing the other way reverse the wiring connections to the lugs.

There is NEVER any guarantee that the diode will be facing the same direction regardless if it is a "genuine" replacement or not.

#11 1 year ago
Quoted from pins4u:

Correct assumption - and if the diode ends up facing the other way reverse the wiring connections to the lugs.
There is NEVER any guarantee that the diode will be facing the same direction regardless if it is a "genuine" replacement or not.

Ah okay, so reverse the wiring rather than flip the diode if it is not facing the same direction - suppose that would at least be easier than bothering to flip the diode! Thank you again!

#12 1 year ago

UPDATE/RESOLUTION: the replacement coil just showed up, I verified the diode was facing the same way as the original coil, got it soldered in, and we are back up and running (w/ replacement transistor and fuse, too, of course). Thanks everyone for your help w/ debugging tips and the like, I very much appreciate you! Glad to have this game up and running again

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