Broken PiDP-8

[Rick Bensene]

ello, all,

Something has gone amiss with my PiDP8.   My PiDP8, 11, and 10 all run on a UPS, and so they are relatively safe from power fluctuations, but still vulnerable if the power is out long enough for the batteries in the UPS to run down.

Not long ago, we had a power outage that ran about 7 hours, and of course, by that time, the UPS ran down.   I wasn't home during this time, so I couldn't shut them all down cleanly before the UPS died.

The PiDP10, and PiDP11 came back up with no problem.  However, the PiDP8 did not seem to be as lucky.  When I powered it up, I got nothing.  No sign of any life on the LEDs and no response to any switches.   

I though perhaps the SDcard image had been damaged due to improper shutdown, so I took it out and re-imaged it.  Same result, no sign of life, although the disk activity light on the RPi 4 that runs the machine did its usual furious blinking as the OS booted.

So I drug out a monitor  and keyboard, and powered it up with them connected, and it appears that LInux boots up fine, and the PiDP8 simh job is running, but still there is no sign of life on the LEDs.   The switches don't do anything detectable, though that's a bit more difficult to tell.

At this point, I suspect that the chip that drives the LEDs has failed.   Either that or some of the GPIOs on the RPi 4 have died as a result of the power failure, but that seems less likely.

I've tried to find that rather odd driver chip on Mouser and various other electronics supply houses, but it's listed as obsolete and not in stock.   I found some on ebay, but I don't trust any chips from that source as there are so many duds/fakes sold there nowadays.

 

Anyone have any idea where I can get one of these chips, or if there's some current-day production chip that can replace it, even if bodge wiring or an adapter is required?/   I'd really like to get my PiDP8 back up and running again.

Many thanks,

Rick Bensene

The Old Calculator Museum

https://oldcalculatormuseum.com

[MogensB]

I remember running an LED test program when assembling my pidp8 - perhaps worth trying? And try a completely different sd card is also worth it, I have seen weird and not obvious errors using a bad sd card which seemed fine after formatting, but wasn’t.

Hope you get it going again! 

https://tangentsoft.com/pidp8i/doc/trunk/doc/pidp8i-test.md

[timr...@gmail.com]

It is possible the "disk" the pidp-8 is using got corrupted not being shut down properly.  I use the word disk but it's just an image.  But I have had my pidp-10 image get corrupted and had to reload it.  And as MogensB suggests maybe try using a different SD card too.  I might have suggested to try to toggle in a small AC count program but I am not sure if your switches are working or not.  Have you tried loading 7777 with Load Address and such to see if any switch works?  I don't know what you have tried so may be suggesting things you have already tried.  Best of luck making it work again.