If I understand the distributor correctly........

The module looks through 2 slotted window radials with an IR beam. The row of 6 slots is the main firing trigger and the single slot is the crankshaft offset for base timing reference.

You can pull the distributor and bench test it with your voltmeter. Look at the harness leads to determine what's what on the distributor connector pins. Apply 12v+ to the positive lead (black w red stripe). Apply 12v(-) to the black lead. Turn the distributor and check for switched 5v+ or so on the green lead - that's the main firing trigger and switches every 60*. The white lead will also toggle voltage, but it's for 1* fine ECU control adjustment below 1500 rpms and idle, so you may not have enough resolution to see this toggle accurately..... but you should still see some movement.