Okay, so you've got 3 MPU-200 games that all use the same SB-300, with the exception of Flight 2000, which has the speech board as well.
Let's start with the SB-300 tests, then.
For each game, measure the following, setting your meter for both DC, and then AC volts, respectively:
- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the MPU.
- Measure voltage (DC, then AC) between TP6 on the SB-300 and ground on the chassis somewhere (the braid is fine.)
- Now, disconnect J3, and measure DC and AC volts from pin 8 of J3 to ground on the MPU, and the chassis somewhere.
We're checking the differential between different bonding points on the SB-300 and other components. Ground pins and
braid might look okay, but since poor bonding leads to a lot of these problems, it's worth the check with the meter.
Then, if you have a clip lead, clip the black lead from your meter to TP1 on the SB-300, and you can leave it there
while you take the next set:
- Measure DC & AC volts at TP3 (+12V)
- Measure DC & AC volts at TP2 (+10V)
- Measure DC & AC volts at TP4 (+5V)
Report back for each game (or even all three at once, if they're handy, and we can talk about next steps.)