On our as-2518-23 for Embryon, a couple of the controlled lamps are locked on. I traced them to q1 and q4.

I think that I may have a bad U1 chip. How do I test that one?

It has been a while for me to get back to this. Any input on direction from you guys would be appreciated.

The symptoms that the lamp driver board show are that q1, q2, q3 q4, q5, q6 and q7 all test within clay's specs (~.5 to .6) when the red lead is is touched to the Gate and the black lead is touched to the Cathode.

I even replaced q3 just to see if that would solve the problem and the result is the same, so I have ruled out the SCRs.

All of those 7 SCRs return no result when the two leads are switched. But the other 50 do.

I noted that all of the other 50 SCRs tested at approx 1.04 which is much lower than Clay suggested at 1.46. I also tested the resistors and they ohm out within a reasonable tolerance level.

Could this still be an issue with U1? Is there a way to test it? It looks like a bear to replace

I actually pulled the main lamp driver board to test it.

**edit - I used Clays guide to test all of the SCR's and when I reversed the leads on my multimeter all but those 7 tested very similarly. Those 7 did not return a value.

To add some specificity, the controlled lamps that are either out or locked on

Locked on during attract mode - q7, q1, q2, q4
Locked on During game play - none
Out during attract mode and game play - q31, q45, q6, q19, q5, q18, q30, q43

At this point it seems unlikely that u1 is the problem since the SCRs in question are tied to multiple decoders.

I suspect that the ones out during gameplay and attract mode are a connector issue at this point.

...seems unlikely to me since we are using a new Alltek MPU...

But the connector issue certainly seems probable.

Well after all it turns out to be a connector that goes between the playfield and A5 J2. It is a 9-pin one that I hadn't built up a corresponding connector from the lamp driver board, J2 connector.