(Topic ID: 311241)

Bally SS Coil Issue. It's something easy. I know it. Please send help. [Solved]

By rockwell

2 years ago

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Latest reply 2 years ago by rockwell
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Embryon Bally, 1981

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I am cleaning up my Embryon, and all of the sudden have a coil issue I can't pinpoint.

Everything was working well until I swapped all the lamps to LED on the playfield. Now, my kickout, knocker, and left slingshot coil won't fire (in game or in test).

I checked power at the coils, all good. I manually fired them by grounding the SCRs, they all fired. So I though maybe it was the SCRs. Replaced those, still happening. I visually inspected and don't see anything shorted. All other coils work. Am looking at connectors now, but they have all been re-pinned/replaced in the last year so doubtful there.

I'm working on this now, any help would be appreciated. I'm sure it's staring me right in the face.

Talk soon!

OP
Quoted from rockwell:
I am cleaning up my Embryon, and all of the sudden have a coil issue I can't pinpoint.
Everything was working well until I swapped all the lamps to LED on the playfield. Now, my kickout, knocker, and left slingshot coil won't fire (in game or in test).
I checked power at the coils, all good. I manually fired them by grounding the SCRs, they all fired. So I though maybe it was the SCRs. Replaced those, still happening. I visually inspected and don't see anything shorted. All other coils work. Am looking at connectors now, but they have all been re-pinned/replaced in the last year so doubtful there.
I'm working on this now, any help would be appreciated. I'm sure it's staring me right in the face.
Talk soon!

It is probably unrelated to the LEDs unless you replaced the lamp driver board at the same time which may have exposed a flaky connector.

Reseat and inspect connectors from MPU J4 to driver J4. All of the momentary signals including the enable come through those two plugs. In the schematic they are labeled something like "SOL-A" to "SOLENOID-D". Very, very common problem. MPU J4 often damaged by the battery leaking and driver J4 prone to get cracked solder joints, among other typical connector issues.

By examining the 74154 truth table. The bally driver board schematic and knowing what coils are a problem, you can find which of the momentary bit's is missing. If there is a connector problem that solenoid bit gets stuck always high because of a pull resistors on the driver board side. The solenoid driver schematic counts in order from top to bottom. Same order at the truth table outputs left to right. Look for a pattern that would happen when one of the A-B-C-D input bits stays as a one/high always and never goes low and then you know what pin is the problem.

It could be something else, but very likely the problem...
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Thanks for the thoughts barakandl . I actually have your MPU in this machine, so we know there's no problems there!

I did go through and re-seat all of the MPU and driver connectors before I read your note, and it did fix the issue. MPU J4 is one connector that hasn't been re-pinned yet, so I will put that on my to-do list. Want to make sure this thing stays working solid!

Thanks again for the note, and for the great products and assistance.

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