On 17/12/2016 18:49, "Tony Duell" <ard.p850...@gmail.com> wrote:
>>> What value resistor? >> >> It's a 5-band red-red-black-black-violet so either 220R or 70k? Based on >> what Pete said about the Z80 I'm going for 220R without pulling it out of >> circuit. >> > > Yes. I would agree with that. It connects to some telephone-based doohickey that can be seen as the right-most light-green module lower centre left of this pic, the one with the red capacitor in the middle of it: http://www.binarydinosaurs.co.uk/stcexecutelboard.jpg Initially I figured the board was divided half and half into phone and digital viewdata with the viewdata part on the right. Now I'm tracing more lines that blur between the pair of them right down the centre, including the source of the 8085's RESET which would seem to be the circuitry in the top-middle of that pic where you can see the battery (now removed). The chip directly below the battery is the RTC, to its left is an MC14081 (quad input AND) and left again is an ICL7611 op-amp. Those 3 have their own 5V supply that's separate from the rest of the board, yay. Not found the source of that yet. >> LS92 since pins 2/3/4/13 are NC. All testing so far has been done with a DMM >> and cheap logic analyser. Since one of the possibly-LS92s is out of circuit >> I'll build a little test circuit to see if it does actually count given a >> clock source... > > > It's not a 7493 as the resets don't match up. I would guess at 74x92 at least > for the moment. See if the rest of the circuit makes any sense. I'm 99% sure they're 7492s now, outputs and inputs match other surrounding chips. Cheers! -- Adrian/Witchy Binary Dinosaurs creator/curator Www.binarydinosaurs.co.uk - the UK's biggest private home computer collection?
