Taxi
Williams, 1988Down to the last thing to fix on my Taxi: the lower pop bumper will not work in test mode or gameplay. This is solenoid #21, special solenoid #5.
Coil will fire when ground lug on coil is grounded to siderail.
Coil will fire when Q77 transistor tab is grounded.
Replaced Q77(TIP102), Q76 pre-driver, U50(7402) chip, and AE23-800 coil.
Showing 40 VDC at both lugs of coil.
I'm plum out of ideas. Any and all help appreciated,
Alan
They appear to be. The pop bumper switches have more wires on them than the same switches in my Bad Cats, but they look good and I don't see any breaks. The EOS switches show up properly in the Switch Edges test, and I can't figure out how a switch problem would prevent the coil from firing in test mode.
Quoted from Alan_L:the lower pop bumper will not work in test mode or gameplay.
This tells you its a MPU problem. It is one of three things 1. U54 2. SR19 3. U49. Do you have a logic probe to test this?
No, I'm afraid not. I replaced U50 because pin 1, which leads to Q76 and then to Q77, read .216 instead of .500's like most of the rest. It still tests in the low .200's along with pin 1 in U49.
Do you know if Sears/Home Depot/Lowe's/Harbor Freight carry logic probes?
Thanks for your help.
This is the logic probe from Amazon http://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4/ref=sr_1_1
recommended in Terry's great guide https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes
Eric
Then turn on power and start a game, and briefly ground pin 19 of U54 carefully. Remember pin 20 is five volts so don't short them together. Each time you ground pin 19 your pop should fire. Let me know what happens.
If you do have 5 volts on pin 19, then start a game and ground pin 2 U49 briefly. Does the pop work each time you ground pin 2.
Measure continuity between pin 2 U49 and pin 2 U50 on the top of the chip legs. You should have 0.1 ohms.
Quoted from Alan_L:U50 pin 3 to R103 (either end) = null reading
Not pin 3, pin 1 U50 to R 103.
Everything sounds like U50 is bad. I know you changed it. Last final test, start a game and ground pin 2 U50. The pop should fire. If not then apply 5 volts to pin 1 U50. Does it fire then?
Quoted from Alan_L:Stumbled across one, the LP-560 recommended by Terry, for $16.97, free shipping
This is a lot easier with a logic probe. You have 10 pins, its a must have.
Yeah, my old probe died.
With game on, grounding U50 pin 2 does nothing.
Applying 5 volts to U50 pin 1 makes the speaker crackle a little bit, but that's all.
I also have a new 7402 chip in U45. If I switch the chips in U45 and U50, will that tell me anything?
Quoted from Alan_L:Applying 5 volts to U50 pin 1 makes the speaker crackle a little bit, but that's all.
Then the pre diver or the TIP is bad. Are you sure you have power on the coil?
Both the pre-driver and TIP haved been replaced. I have a good 40.2 volts at the coil lug, same as the other two pops. It does fire when the coil ground lug is grounded and when the TIP is grounded.
Let me check around the TIP and p-d for conicity and maybe I have a broken trace or something.
I'll get back in touch when my logic probe arrives.
Thanks for your help,
Alan
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Jarrettsville, MD