I am helping a friend with this machine and the schematics on ipdb are hard for me to read. Can someone tell me which transistor is likely the culprit?
I think that it is Q10 which is a tip 120. I also believe that it is what drives pin 8 on the 2J12 connector.
A verification would be appreciated.
Firstly, are you positive the switch isn't being sensed as closed?
Transistors can test as good, but be bad, although in this case I would expect to read a short on the driver transistor if it was the problem. If you have a logic probe check the input to the driver and pre-driver transistors. You can also get a reasonable reading with a meter.
As an update, here is what I saw when I went to my friends house to help him with the Gorgar:
The Q10 transistor (tip 102) and the pre driver have previously been replaced, as has the right slingshot coil. Presumably this problem has popped up previously and someone replaced all 3 items. That didn't work.
So, they presumably pulled the blue wire on connector 2J12 (pin 8 ) for that solenoid and sold the machine to my friend (a newbie with the itch since he has amassed 10 already over the last year).
I tested Q10 and the predriver as well as the coil's diode and they all tested within spec and similar to neighboring components.
I also pulled the 2N11 connector, which is the switch inputs, then re-connected the blue, pin 8 wire on 2J12, and the coil immediately locked on.
I believe that I have ruled out a bad switch, coil diode, switch diode, driver trans and pre-driver trans.
I suspect that the problem lies on the MPU/power driver board. So on vid's list above it would seem that it is a bad 7402 or bad PIA.
Any indication which component those two items are?
Thanks all!
With your voltmeter, measure the inputs to IC 9 pins 5 and 6 and compare with inputs to IC 8 pins 8 and 9 with the game in attract mode. If these input voltages measure the same i.e. IC 9 pin 5 matches IC 8 pin 8 and IC9 pin 6 matches IC 8 pin 9 you can conclude as is well upstream from the 7402.
Next cut IC 9 pin 4 to where you can resolder the gap. This is the output of the 7402. If the solenoid still locks on when you connect the wire then the problem remains as the pre-driver and driver transistors. If the problem is gone then replace IC9
Chances maybe that the previous person replaced the driver transistors, then found that the coil was bad and then replaced the coil but had burned out the recently replaced driver transistors or maybe the switches were stuck or shorted closed associated with the kicker and burned out the replaced drivers and the coil.
I would double check the coil resistance, lift the diode and test or replace it on the coil. Then replace the pre-driver and driver transistors and fix the cut on IC9 pin 4.
The other thing is that sometimes new components can be bad not frequently, but it does happen. Also, faulty components can test good but not function correctly.
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Tucson, AZ
Sana'a