So, one bazillion dollars to whoever figures out the cause...
There I was... Eating, Drinking, and being Merry while playing my TZ. Suddenly, out of nowhere, the machine gives me a switch error then dies. So after coughing up the Cheetos I started to choke on, I tried restarting the machine. No Joy... all I get are the LEDs D19 and D21, no blinking D20. When the machine it turned on, only those two LEDs are solid, no blinks or anything from D20. The nerve of some machines!
Tested all voltages, what I have found is that the board is getting the proper voltages with the exception of U21 pin 3. There is no 5vdc coming from that pin on that chip. I am however getting 5vdc going to the banded end of the diode at D25, however the non-banded end is not registering any voltage. Easy fix right? Just replace the diode you say? Well I did and no change! In fact, what I have found is that when the non-banded end of the diode is removed from the board, it registers 5vdc however as soon as I touch it to the board, bahhm! Voltage drops! When I remove C50 and R90 the diode at D25 will keep it's voltage after attaching back to the board. However as soon as I put C50 or R90 back in, the voltage drops again.
I did remove the board from the game BTW and am in the process of bench testing it with a switching power supply.
Replaced the following chips with working ones from my IJ:
Replaced the following chips and components with brand new ones:
Still no joy. Tested voltage at U10 pin 1 and am getting 4.85vdc.