Stern High Roller Casino (Stern, 2001) won't boot up

[knit]

High roller casino won't boot up,no display or control lights(only GI lights) and LED L204 is blinking.
I swapped the I/0 board with my working sopranos and it worked perfect so I'm pretty sure problem is in I/0 board
All fuses have correct voltage
all 5v, pins 4 to 8 at J16 are 5v or more
I tested U6: pin 19 is low and no pulsing, pin 1 stays low and flashes to high insync with LED L204 all other pins low except 11,and20 are high
test points:
Reset has 2, top pulses from high to low about every 1/2 second
Bottom stays high
TIP1 TPL3 stays high
TPL1 FET stays high
test points:
Reset has 2, top pulses from high to low about every 1/2 second
Bottom stays high
TIP1 TPL3 stays high
TPL1 FET stays high
All LED are lite except LED L204 (blinking)
blanking stays low and flashes to high insync with LED L204's blinking
I'm not too familiar with using a logic probe and not sure what to test next
Thanks so much

 

[pinballdaveh]

I don't have any experience with sterns white star boards repairs. Of what I can tell u6 is part of the watchdog circuit that monitors low 5 volts. If all LED's are lit and bright maybe the problem is elsewhere. Is there chips that decode the data signals from the cpu that could be locking up the start up? Maybe rob kahr will see this post and chime in to help. Or maybe someone on pinside has seen this problem and can help. Sorry most of my experience is with EM's and early SS games. A last resort is to send the board out for test and repair.