(Topic ID: 234888)

System 11 Special Solenoids

By ngreenup

5 years ago

Topic Stats

4 posts
3 Pinsiders participating
Latest reply 2 years ago by Inkochnito
Topic is favorited by 5 Pinsiders

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Pinbot Williams, 1986

Here is the short version

Before doing work, q69 was roasted but everything else worked and no fuses blew. After attempting to fix... more issues.
Now all special solenoid drive transistors except one have a open path to ground with connector J19 connected but do not with it disconnected. Fuse special solenoid fuse on power driver blows if J19 is connected. Is SN74F02N a compatible replacement for 7402 and U45?

More complete description

I have been fighting with a new to me Pinbot's special solenoids. after removing everything top side of the playfield, cleaning it, and re-assemblng, I started the solenoid tests. The left sling shot wouldn't fire so I opened up the backbox and noticed the typical roasted transistor (Q69) for this left sling special solenoid. So I took the board out and changed Q69 and the predriver. While I was at it I changed all the caps on the PSB board as well. I started a game and again the left slingshot would not fire and it appeared the transistor burnt up again. I say appears because now I am unsure, but keep reading. This time I changed the transistor, the resistors at R93-R94, and the 7402 chip at u45. I used a SN74F02N, perhaps that is the issue but I was told it is a valid replacement in this scenario.

Now when I try to play test, it seems any of the special solenoids will cause the fuse to blow on the PSB. So I did a quick test on each of the special solenoid drive transistors by checking continuity to ground and ALL OF THEM except one had continuity with ground with the game off and everything plugged in. Removed the board and checked them and all came up fine and not grounded except q69. So then I plugged in ONLY J19 and they all had path to ground again.

I am kind of out of ideas. It seems I have a short here but I cannot find it. Unless another component has failed or the SN74F02N won't work in this application.

I am willing to start completely over with my trouble shooting. It seems I have made things worse. This is far from my first system 11 repair and my second pinbot. But it's best to pretend I know nothing. I can't wait to figure out what simple thing I am overlooking.

The special solenoids are controlled through a pair of 7402s that are NOR gates. In order for that gate go high and trigger the 2n4401, both inputs to the gates have to be low. One of the inputs is always held low by U56 when the special solenoids are engaged (it also controls the flipper relay). The other input is supposed to be triggered through the incoming connections from the switches on the special solenoids. However, there is one component all the input lines have in common: SR20. When the control switches are not triggered, this is supposed to provide +5v to the 7402 inputs to keep the NOR gates closed. I suspect that if you are not getting the +5v through it, your input signal to the 7402 may be floating low, and triggered all of the gates. You can check this with the board installed, the game in test mode, and J19 unplugged, measure the input voltage to the NOR gates at U50 and U45. You should see a near 0 volts at the input off of U56, and the other input coming off of SR20 should be +5v if things are working correctly.

I've had the same kind of problem with this kind of board.
Replaced both transistors and verified U45, U50, U49, all good.
I still had the problem.
In the switch circuit is also a zener diode 1N5234 6.2V to prevent high voltage into the circuit.
This zener diode was blown and "kept the switch made", thus activating the transistor, burning the coil and/or blowing the fuse.
Replaced the zener and all was good to go.

Quoted from Inkochnito:
I've had the same kind of problem with this kind of board.
Replaced both transistors and verified U45, U50, U49, all good.
I still had the problem.
In the switch circuit is also a zener diode 1N5234 6.2V to prevent high voltage into the circuit.
This zener diode was blown and "kept the switch made", thus activating the transistor, burning the coil and/or blowing the fuse.
Replaced the zener and all was good to go.

The same goes also for all the Data East cpu boards....

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