Gottlieb driver board swapped for a light issue

So, two lights on the playfield are tied to one transistor. They are always on. So I have another good driver board, and out of curiosity I switch the board out. Now those two lights are always off.

So the transistor is probably fine. Not sure what this result indicates. What do you think? MPU? Something else? Thanks

#2 1 year ago

CHD

Cheddar

I'd diode test the driver for that lamp (in the schematics) against one of the others you know is working. I'm assuming the stuck on lamps were due to a shorted driver and on the known good board they weren't lit by design.

The power is always present at the lamps and the driver provides a path to ground to light it. If the driver isn't shorted is there any path to ground on the board? ( could be a flattened driver or solder splash). You can test continuity from the socket to ground and that will tell you if there is one.

Then each light driver is tied to the output of a Latch Flip-Flop Z1-Z12 these basically just hold a lamp off or on until the group of 4 attached to it is set to the next state. Since all the other lamps are working fine we can assume the wiring from the mpu to the driver is good otherwise 11 other lamps would have the same problem. I'd diode test the flip-flop associated with these lamps and compare it to another on the same board that is working. It's possible the flip-flop is locked on for that driver

#3 1 year ago

MtnFrost

Inactive member

Quoted from Cheddar:
I'd diode test the driver for that lamp (in the schematics) against one of the others you know is working. I'm assuming the stuck on lamps were due to a shorted driver and on the known good board they weren't lit by design.
The power is always present at the lamps and the driver provides a path to ground to light it. If the driver isn't shorted is there any path to ground on the board? ( could be a flattened driver or solder splash). You can test continuity from the socket to ground and that will tell you if there is one.
Then each light driver is tied to the output of a Latch Flip-Flop Z1-Z12 these basically just hold a lamp off or on until the group of 4 attached to it is set to the next state. Since all the other lamps are working fine we can assume the wiring from the mpu to the driver is good otherwise 11 other lamps would have the same problem. I'd diode test the flip-flop associated with these lamps and compare it to another on the same board that is working. It's possible the flip-flop is locked on for that driver

Thanks, I'll test it. I just got the schematics for this one, so made it real easy to trace the line back.

#4 1 year ago

MtnFrost

Inactive member

Quoted from Cheddar:
I'd diode test the driver for that lamp (in the schematics) against one of the others you know is working. I'm assuming the stuck on lamps were due to a shorted driver and on the known good board they weren't lit by design.

Question on this though - the two driver boards are the same. So unless we had the incredible rarity of the exact same transistor issue (and no other lamp had an issue), it cannot be the driver board or any components on it, right? So it wouldn't be a latch flip-flop because those are on the driver board, and we know that the odds of both driver boards having the exact same issue on one, and only one lamp are astronomical. Or did I miss something? Just trying to understand.

#5 1 year ago

CHD

Cheddar

I'm assuming the lamps weren't supposed to be on. That's more likely. It's also possible based upon what lamps they are they may not be lit most of the time. You never mentioned which lamps they were.

BUT. we know the wiring and the power is fine because they were on. And we know it's not the mpu because 11 other lamps would have the exact same behavior. The same 4 lines are used to toggle the lamps on each flip flop. Only the chip selection changes.

SO are those lamps supposed to be lit when you are looking at them? Because your first post made it seem like they were always on. Do they light in lamp test with the new driver board?

#6 1 year ago

MtnFrost

Inactive member

Quoted from Cheddar:
I'm assuming the lamps weren't supposed to be on. That's more likely. It's also possible based upon what lamps they are they may not be lit most of the time. You never mentioned which lamps they were.
BUT. we know the wiring and the power is fine because they were on. And we know it's not the mpu because 11 other lamps would have the exact same behavior. The same 4 lines are used to toggle the lamps on each flip flop. Only the chip selection changes.
SO are those lamps supposed to be lit when you are looking at them? Because your first post made it seem like they were always on. Do they light in lamp test with the new driver board?

Ah, I see. These are lamps that should flash on and off during the attract mode, and then are off until conditions are met while playing the game, then they are on until the ball drains. I put the first board back in, so now these two bulbs controlled by Q20 on the driver board are locked on at all times.

#7 1 year ago

CHD

Cheddar

Most likely Q20 is shorted. You can diode test it with a dmm and compare it to a neighbor of the same type.

#8 1 year ago

MtnFrost

Inactive member

Quoted from Cheddar:
Most likely Q20 is shorted. You can diode test it with a dmm and compare it to a neighbor of the same type.

Following up. Yes, that was it. Stealing one from the other board fixed it. I did do the diode test on both good and bad transistor, the bad one showed a short. But the good one didn't give me any readings between base/emitter or base/collector. I thought I should see some sort of 0.3-0.7 vdc drop. Ah well, thanks!

#9 1 year ago

CHD

Cheddar