Re: [vcf-midatlantic] PDP-8/L restoration
On Thu, Dec 26, 2024 at 9:03 PM Mike Rieker via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
If anyone is interested
Seriously interested! I have been trying to add mass storage to my PDP-8/L since I got it in High School in the early 80s! There were only a few options then and I never encountered any for sale at a price I could approach.
I finished a Zynq thing that plugs into the back of my PDP-8/L to provide disk, tape, tty functionality. The thing actually boots and runs OS/8!
Outstanding! That's been my goal all along - boot OS/8 on an -8/L.
Anyway I made an Hackaday page https://hackaday.io/project/202048-pdp-8x2fl-enhancements
Nice photos. Would love to see more detail.
About all I had to do to get the PDP running was replace a few (half dozen or so) 7400 series chips, some corroded diodes on the core stack and a power resistor. Hasn't missed a beat since.
Sure. In my years of maintaining gear from that era, I find a lot of dead 7474 and 7440 and some dead 7420 make up 90% of the bad ICs. Every once in a while, a diode.
I don't know if any of you have interest in this sort of thing. I don't have a PDP-8/I but it might not be too difficult to adapt it to one of those or other PDP-8s and maybe 11s.
I think most PDP-8/i are negibus, and the -8/i itself is expecting to implement memory expansion to 8K internally (including using an M702 "memory detector" card in a particular slot). I have a 4K -8/i that I tried to upgrade to 8K when i was still learning (and lacking in the PDF scans we have now) that I was unsuccessful with due to my lack of deep understanding of how all the parts work (G020 -> G021 was one I totally missed as a teenager). It might be easier on an -8/i to remove the original memory parts and just use the Zynq board for all 32K (or do what was somewhat common back then, 8K with DEC parts and "external 24K" which _was_ done with non-DEC expansion boxes). I would definitely love to learn how to get one or two of these. Not as interested in the frontpanel emulators. I can see how they are handy but I'd prefer the original look. Thanks for sharing! -ethan
On Thu, Dec 26, 2024 at 9:03â¯PM Mike Rieker via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
If anyone is interested
Seriously interested! I have been trying to add mass storage to my PDP-8/L since I got it in High School in the early 80s!
There were only a few options then and I never encountered any for sale at a price I could approach.
I finished a Zynq thing that plugs into the back of my PDP-8/L to provide disk, tape, tty functionality. The thing actually boots and runs OS/8!
Outstanding! That's been my goal all along - boot OS/8 on an -8/L.
Anyway I made an Hackaday page https://hackaday.io/project/202048-pdp-8x2fl-enhancements
Nice photos. Would love to see more detail.
About all I had to do to get the PDP running was replace a few (half dozen or so) 7400 series chips, some corroded diodes on the core stack and a power resistor. Hasn't missed a beat since.
Sure. In my years of maintaining gear from that era, I find a lot of dead 7474 and 7440 and some dead 7420 make up 90% of the bad ICs. Every once in a while, a diode.
I don't know if any of you have interest in this sort of thing. I don't have a PDP-8/I but it might not be too difficult to adapt it to one of those or other PDP-8s and maybe 11s.
I think most PDP-8/i are negibus, and the -8/i itself is expecting to implement memory expansion to 8K internally (including using an M702 "memory detector" card in a particular slot). I have a 4K -8/i that I tried to upgrade to 8K when i was still learning (and lacking in the PDF scans we have now) that I was unsuccessful with due to my lack of deep understanding of how all the parts work (G020 -> G021 was one I totally missed as a teenager).
It might be easier on an -8/i to remove the original memory parts and just use the Zynq board for all 32K (or do what was somewhat common back then, 8K with DEC parts and "external 24K" which _was_ done with non-DEC expansion boxes).
I would definitely love to learn how to get one or two of these. Not as interested in the frontpanel emulators. I can see how they are handy but I'd prefer the original look.
Hi Ethan, I am going to make some 'V2.0' Zynq boards, basically heavier drivers to work against the 8/L's pullups. The current chips are 25mA which technically work with the 220-ohm pullups but is right to the limit. Plus I since found some 180-ohm pullups buried in the M220 boards which puts it a little over 25mA. The "0" voltage is like 0.6-0.7V which is a bit high for my liking though it seems to work fine. But anyway I'm going to do some new boards with 100mA transistors. If you want, I can have some extras made. I have the PCB company assemble the surface mount parts then I solder the through-hole stuff myself. I'd have to see how much extra it costs to have more boards made. If you want to do it yourself, the github page has all the PCB files in the zturn directory. https://github.com/mrieker/pdp8l You'd need one each of the zturn36,35,34b,34d boards, plus 3 of the zturnic boards (interconnects the others). The ZTurn-7020 boards come from MYIR and are around $150. The front panel thing is just for testing. We cleaned the front panel up and replaced all the light bulbs (a few were dead). I have the idea that maybe I can somehow tack a RasPI onto the real front panel. Or if not, maybe make a replacement circuit board with a RasPI and LEDs. But I'd have to move all the switches over so not sure if I want to do that. Mike
Thanks for sharing!
-ethan
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Ethan Dicks -
wmrieker＠nii.net