gamefixer
Well-known member
Here's hoping you can answer a couple of questions for me that might also prove useful to others in the future.
I'm trying to use a logic probe on the cpu board. Where would I be able to clip the red and black leads on the cpu board to power the thing? The test points for +5?
I'm trying to probe the "coin drop" signal; if I ignored the logic probe and tried to use my DMM, would that likely pick up the coin drop pulse or would it probably be too fast for the DMM to register?
At the moment I'm trying to probe pin 9 of the 74LS00 in U6 but I'd want to hit pin 10 as well for the switch NO line and pins 12 and 13 for the NC line.
Edit: I found some +5 and ground connections on the Z80 but I can't possibly clip the alligator clips on the logic probe to chip legs, they're way too big. What to do?
Since I've got an ATX supply powering my board set I get +5 and GND from one of the molex connectors on the supply.
If you're testing in a cabinet the safest place to get them would be directly from the power supply. But, according to the cabinets wiring diagram pin 2 of P1 should be brown which is +5. You should be able to use any of the large grounding braids as your GND reference assuming your connection from logic GND to earth GND is good.
If you're on a workbench get your +5 and GND from the power inputs on the board set or from the power supply. There are a few GND posts on the CPU board.
the end result of the coin circuit that you are testing is at pin 6 of U9, Id start there and work outwards. A DMM will register a change but it wont be fast enough to see if your getting a good "state change" unless the meter has the ability to record (some flukes do) then you could look back at the results.
You could also probe at the coin switch to make sure your connections to the board set are good as well as the resistor pack at RP3. Which ever coin input that IS NOT connected to ground should go high. If they dont you have a broken wire or that resistor pack is bad. I'd go with broken wire.
