The first thing that comes to mind on the 8/a is whether or not the front panel (key press is what I assume you are using, cables are plugged into the board the proper way.
On Mon, May 11, 2020 at 5:10 PM Bryan Longram via cctalk <[email protected]> wrote: > > I acquired a non-functional PDP-8/A several months ago and in that time I've > replaced all the outwardly damaged parts and have gotten the machine to power > on with no issues. However the problem I've been having now that I can't > quite seem to pin down is that every time I power the machine the address > field is displayed as 07777 and the value field is displayed as 7777. > Attempting to change addresses or the value of the address doesn't work as I > can enter the value just fine but upon entering the Load Address button it > defaults back to being all sevens. I've made sure the pins on the CPU board > are set so it should start at address 0, the advanced options are also all > turned off and as far as I can tell there's nothing out of the ordinary with > the pin settings on the IO board. > > I'm fairly certain at this point that the issue is with the Programmer's > Panel but I'm not 100% sure. > > I've done some further testing using advice I got from users over at the > Vintage Computer Forum and SR and LSR work as intended, I can enter a value > into SR and then view it at a later time. Something interesting I did find > was while checking over the CPU I was looking at the switches on it and while > S1-1 was set as expected S1-7 was also on which is the CPU autostart disabled > feature. > > Upon powering the computer back on after turning S1-7 off both the ADDRS and > DISP displays show a single 0. I thought I was on the right track though now > the panel doesn't work as if the panel lock was toggle even though it's not, > not even the read functions and SR are working. Switching S1-7 back on > reverts the problem back to what it was before and far as I know all the > voltages on the power supply are correct. Any help would be appreciated, even > if it's just a push in the right direction.
