(Topic ID: 235756)

Stern "PinBall" game rendomly resetting


By gchase

1 year ago



Topic Stats

  • 4 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by dothedoo
  • No one calls this topic a favorite

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#1 1 year ago

I have a 1977 Stern Pinball machine that randomly resets. The game has the alltek ultimate MPU and SDU boards. I checked 5 volts on the MPU board and got 4.7 which was a little low but I think OK. On the SDU it reads 4.9. So I decided to check other voltages. Checking the voltages at the rectifier board I found 15.6VDC on TP3 instead of 11.9VDC. I checked the voltage from the transformer for that circuit and found 13.2VAC which seemed a little high but not 15.6. I thought I might have a short so I pulled fuse F3 and the TP3 went to 0.

I am baffled how I can have more DC Voltage out than AC voltage in? Not sure if this is the cause of my reset problem but it is a problem. I am surprised that something has not smoked with the voltage that far out of range.

Any thoughts would be much appreciated.

Gary

#2 1 year ago
Quoted from gchase:

I checked 5 volts on the MPU board and got 4.7 which was a little low but I think OK. On the SDU it reads 4.9

That's a problem, you're getting voltage loss through the connectors and 4.7V at the MPU board is too low for reliable operation.
Were the wire connectors reterminated when the new Alltek boards were fitted?

Quoted from gchase:

Checking the voltages at the rectifier board I found 15.6VDC on TP3 instead of 11.9VDC.

There's a capacitor on the solenoid driver board that's storing energy to filter out most of the DC ripple. It results in raising the DC voltage. If you disconnect J3 (backbox harness) from the rectifier board, TP3 will then measure closer to your expected voltage value.

#3 1 year ago

Almost always, "random" = "connectors".

#4 1 year ago
Quoted from cody_chunn:

Almost always, "random" = "connectors".

Yep, repin J4 on the MPU for sure and J3 on the SDB.

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