I have a recently acquired 3456a.
On power up it indicates overload and it fails self test 4.
After poking around the A20 (A/D Converter) board, I concluded that the analog circuits seemed to be working OK and that the OL was due to the control inputs.
Swapping the A30 (Inguard Logic) board confirmed that it was bad.
HSA output is always high. Followed that back to the 8048 pin 29 which is always high.
8048 seems to be executing. ALE is present. pins 27 (HSC) and pin 28 (HSB) toggle. ROM test passes.
So I think the 8048 is bad. But it is hard to be sure since relationships between the inputs and outputs of a microcomputer can be very complex.
Is there anything else I should look at?
Is the 8048 rom contents available so I could program a 8748?
