Hello,
I finally got my Space Shuttle to reveal it has an error Code 7 on the 7 digit display. I say finally because I discovered the display was bad and U8 (the 7447 chip that sends signal to the display). The board is on the bench with a PC power supply feeding it +5vdc and +12vdc. Almost all of the IC chips have been replaced along with all the PIA’s and CPU chips.
Here are some symptoms I am seeing. Chips U1, U2 get extremely hot within 30 seconds of power up. On U17 pin 20 reads high/low with logic probe, but the high light pulses very fast. Pin 18 does the same except the pulse rate is slower.
My reset voltage is 4.86 volts and makes it everywhere it is supposed to. All the electrolytic caps have been replaced.
What Can I do to diagnose the cause of my error code 7?
Thanks

Let’s say that all those items mentioned in the pinwiki check out. What Else could it be. When it say problem with IRQ circuit, does mean bad PIA’s. Could it be as simple as a bad R168 3.3K ohm resistor?