No, you’re right, did you look with a scope at the bus signals?
You should check if all bus signals are transferred to the keyboard and option rom boards.
On the rom connector board you’ll find a bus driver ic you should check if the bus signals are on both sides of the driver.
Another thing the 9825 can boot without the tape controller board, so to check if it doesn’t hang the system you can disconnect it and try to start the computer.
The tape controller board is the board above the processor with the cable to the tape drive.
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