The GI circuit is 6 VAC.

Normally if you are reading a high voltage on a column the signal is staying high rather than being pulsed. Although 4 volts sounds way too low for the pulsed signal. Are you using a decent meter?

Check all of the column drives and see how each one reads. If one is high then there's a problem with the board.

http://pinballrehab.com/1-articles/solid-state-repair/repair-guides/148-lamp-matrix-theory-and-troubleshooting

Easiest thing to do is disconnect the lamp column connector and then check each of the column pins. Since the signal is pulsed you should get about 12 volts. If any of the columns read at 17 volts then that column is locked on rather than pulsing.

Yes.

I would guess that's just the quality of the meter. Even expensive meters have difficulty with pulsed circuits since that isn't that they're designed for.

Start making your way back up the circuit until the column in question matches the other columns. If you have a logic probe that works even better since you can see the pulses.

I think system 11's have a resistor pack that pulls up the columns. If so, give it a squeeze and if it crumbles then that's your issue.

I doubt if they do, it's just a cheap meter.

U52 provides the pulsed signal (5 volts) which needs to be raised to 18 volts and handle higher current. That is the purpose of the two transistors. Same signal across the circuit, just at a higher voltage/current level.

Take readings at the red circles, and you can compare that to the blue circles.

433348-a.jpg

The best way to see the traces on the board is to backlight it and then you can see the traces on both sides. This isn't always feasible so use your meter set on diode/continuity to figure out which points connect.

On the SR's the dash number is the pin number, so SR-9 is pin 9. Pin 1 should have a dot on it.

We'll do the red circles. The one on the right will be on SR16 pin 9 (this should directly connect to R83). The middle red circle can be checked at U52 pin 11. The left circle can be tested at U52 pin 12.

Here's some info on reading schematics.

http://pinballrehab.com/1-articles/solid-state-repair/tutorials/234-electronics-tutorial-reading-schematics

And the entire series (the better choice, but a lot of reading).

http://pinballrehab.com/1-articles/solid-state-repair/tutorials/147-solid-state-pinball-tutorials

Where's zaza and his wonderful graphics when you need him?

Thanks zaza.

Man you kids have good eyes.

I was a vibrant 50, now I'm a less than vibrant 61!

I agree 100% on the visual inspection--you can find a lot of problems that way. The most troublesome for me is photographs for some reason.

Basically yes. The input to the transistor is pulsed (lo and hi) and the output should be pulsed. Instead the transistor is shorted and sending constant voltage to the lamps.

Good catch barakandl.