I have a Williams system 6 mpu I'm working on. Both leds are stuck on. I've gone over the board and checked everything, clock, chip select, vma, reset, activity on the data bus and Address lines. Blanking never comes up, I've pulled the processor, pia, rams, and ROM and tested them on a working mpu and they all work. I've replaced all the sockets and the 40pin header checked for shorts, everything is good there. I'm testing this on a Williams factory test fixture with a tested and working solenoid driver board, power board, displays. This one has me stumped.

And if I pull the pia chip, the upper led goes out but the lower stays lit.

Finally had some time to work on this. I started looking into the chip select area as i noticed on my scope it was dead. Found pin 3 of ic12 (7408) stuck low. Replaced that ic and board works as it should.