I don't understand Tony's measurement of 38,39 HIGH, on my schematic pin 39 is connected directly to ground.
Tracing back the input for the RST5.5 pin, in the absence of the GPIB board there is precisely nothing connected to pin 14 of U472. Leaving a TTL input unconnected is normally not good practice, I am surprised if Tek would have done that, but unconnected TTL inputs float high and the conclusion must be that in normal operation the CPU would check for the presence of the GPIB board and if not found it would leave the RST5.5 interrupt masked off.
John, when you said you had looked for a burst of activity on the cpu pins immediately after reset were you using a normal analogue scope or a scope with single shot storage? The processor activitiy could only be for 10s of microseconds and easy to miss on a normal scope.
I noticed the RAM on the 8085 board is made up of 2114s, I seem to remember a thread on one of the UK forums where these were regarded as failure prone but I have no personal experience with these.
The two programmed 28C64s are in the first class post (don't hold your breath). I hope making the adapter boards is not too much hassle, a lot depends on the room available.
Roger
