This system 6 MPU board was a working board until I pulled IC7 to test on another board. I replaced the 74041N at IC7 and with Pincoder's ROM 1a I should get an alternate flashing of the top and bottom LEDs. Now all that I get is the flash of both lights, then the top light stays on. Notes below on what I get when testing
IF YOUR BOARD FAILS THIS TEST
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Check the board for the following:
1) Check for pulses (alternating high/low signals) on IC1 pin 5 (VMA). This is important
because it shows the CPU is executing instructions.
Pin 5 is not pulsing and is HIGH
2) You should also be seeing pulses on IC8 pins 14,13,3.
There is no pulsing on 14,13,3 and is HIGH
3) There should be pulses on IC18 Pin 6 (PA4) and pin 7 (PA5). If not PIA1 *could be* bad.
There is no pulsing on 6,7 and is HIGH. I also changed the PIA with the same results
4) Check that PIA1 pin 39 (CA2) is high and that IC2 pin 1 is low. If not IC2 will not
light the LEDs. There is an inverter (IC7 Pins 11:high, 10:low) between these two points
that performs the signal transition here.
PIA 1 Pin 39 is LOW. IC2 pulses HIGH and LOW, IC7 pin 11 is HIGH and pin 10 is LOW
5) Check that pin 15 on IC2 is low enough to be considered a logic 0 and that SW2 is
open. Check that R19 is 4.7k and is connecting to ground on one side.
Not sure how to check pin 15 on a 14 pin IC. SW2 is open and R19 is correct.