High Speed
Unidesa, 1986Currently trying to figure this one out. My under playfield blue flashers on the left side are stuck on when the game is turned on. I replaced both the transistor and the pre-driver on the CPU board but there's been no change. All of the other flashers (including the right side blue ones) are working correctly.
Hoping someone can point me in the right direction.
Thanks!
Quoted from cfh:Are you using LED flashers? If so, that's your problem
I am not using LEDs.
Quoted from wayout440:Get a measuring device (logic probe, DMM, or o-scope) on pin 3 of U19. Is it stuck on logic high?
Can you walk me through this a bit more? My knowledge of integrated circuits is pretty non-existent. I put my DMM in signal mode. Touch black to ground and red to the pin? Do I need to have bulbs in the socket?
When I do this my right blue flashers (which work correctly in game) turn on and stay on while my probe is touching. DMM reads 1.
Quoted from frisbez:I am not using LEDs.
Can you walk me through this a bit more? My knowledge of integrated circuits is pretty non-existent. I put my DMM in signal mode. Touch black to ground and red to the pin? Do I need to have bulbs in the socket?
When I do this my right blue flashers (which work correctly in game) turn on and stay on while my probe is touching. DMM reads 1.
You don't need to have bulbs in the socket for this test. Like cfh said, remove the two lower left connectors on the bottom of the board (1J11 and 1J12) to see if the lights go out. That will help determine if there is a problem with the control from the MPU, or if it is a wiring/playfield problem.
Looking at the schematic and coil table, the left blue flasher is switched by Q31 which in turn gets a logic signal from pin 3 of U19. If you are touching the probe to that pin and the RIGHT blue flasher comes on, I am a bit miffed by that. Another test you can do is to use an alligator clip lead/jumper to turn on the flashers in question. Attach one lead to ground and then briefly touch the tabs of Q31 and Q23. Q31 should turn on the left blue flasher, and Q23 should turn on the right blue flasher (of course, this won't mean much to the stuck on flasher - but it does help confirm the solenoid table in the manual vs. the wiring to the flashers)
Not sure about your signal mode with the DMM. I simply use DC volts.
Also, find the flasher resistors for the lamp in question under the playfield are all correct and soldered.
Quoted from wayout440:You don't need to have bulbs in the socket for this test. Like cfh said, remove the two lower left connectors on the bottom of the board (1J11 and 1J12) to see if the lights go out. That will help determine if there is a problem with the control from the MPU, or if it is a wiring/playfield problem.
Looking at the schematic and coil table, the left blue flasher is switched by Q31 which in turn gets a logic signal from pin 3 of U19. If you are touching the probe to that pin and the RIGHT blue flasher comes on, I am a bit miffed by that. Another test you can do is to use an alligator clip lead/jumper to turn on the flashers in question. Attach one lead to ground and then briefly touch the tabs of Q31 and Q23. Q31 should turn on the left blue flasher, and Q23 should turn on the right blue flasher (of course, this won't mean much to the stuck on flasher - but it does help confirm the solenoid table in the manual vs. the wiring to the flashers)
Not sure about your signal mode with the DMM. I simply use DC volts.
Also, find the flasher resistors for the lamp in question under the playfield are all correct and soldered.
The resistors seem to be soldered on correctly.
I unplugged the connectors and both sets of blue flashers did not turn on.
Next I replugged the connectors and turned the game on. But now my left blue flashers are not on when the game starts. Progress? Unfortunately no. I go into coil test, and they don't fire. I also tried starting a game and testing them with inlanes. Still not turning on. So now rather than being stuck on they just don't turn on at all. I did notice however that they turn on for a split second when I turn the game on.
I also noticed that my right side red flashers aren't working now (they previously were). The manual is telling me that they are controlled by U18 rather than U19. I'm not really sure what's going on. Anyone have a next step for me to try?
Thanks for all of your help so far wayout and cfh! I'm determined to get this figured out.
Looks like a board problem now. With the change in now the red flasher troubles, possibly a PIA (I think U10) Neither U18 or U19 actually "control". They are more or less a pass through, enabled only when blanking tells them it is ok to do so. You would need to troubleshoot by examining the PIA signals and U18/U19 signals in and out to determine which to go for.
Quoted from wayout440:Looks like a board problem now. With the change in now the red flasher troubles, possibly a PIA (I think U10) Neither U18 or U19 actually "control". They are more or less a pass through, enabled only when blanking tells them it is ok to do so. You would need to troubleshoot by examining the PIA signals and U18/U19 signals in and out to determine which to go for.
I checked the game before work this morning it is back to it's original behavior. Left blue flashers stuck on, right blue and both sets of red flashers working correctly.
I checked the CPU schematic and it does look like you're correct about U10 controlling the solenoid drivers. If I purchase a new PIA for U10 and AND gate for U19 is there anything else that might also need to be replaced that I should buy with them?
Quoted from frisbez:I checked the game before work this morning it is back to it's original behavior. Left blue flashers stuck on, right blue and both sets of red flashers working correctly.
I checked the CPU schematic and it does look like you're correct about U10 controlling the solenoid drivers. If I purchase a new PIA for U10 and AND gate for U19 is there anything else that might also need to be replaced that I should buy with them?
Remember, shotgunning is just a guess. troubleshooting would tell you more. You could have other things wrong. The PIAs could be getting faulty instructions or you could have problems elsewhere. You're rolling the dice by replacing those components blindly.
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Kent, WA