At present, there seems to be a rather troublesome circuit board, M8139 TIG, which uses too many things that cannot be found. I feel that using modern components and rebuilding according to the functions described in the manual may be better
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About re-producing PDP-11/70
- Thread starter alphaaxp
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ggs
Experienced Member
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Terri Kennedy
Experienced Member
The TIG is a mystical board. It generates (as the name implies) the timing for the CPU. It cannot be adjusted on an extender board, and there's no way to adjust them in the card cage due to adjacent boards. I've been told that there were only a handful of people at DEC (and one super wizard) that could calibrate them.
AK6DN
Veteran Member
The 11/70 TIG is an updated clone of the 11/45 TIG. IIRC the 11/45 TIG was done by Rob Holt. Al Helenius cloned it for the 11/70.
Later 11/70 TIG update ECOs were done by Ray Boucher whom I worked with directly as he was one of the designers working on the 11/74 CIS project.
To whomever gets the task of producing an 'updated' 11/70 TIG design I say you are going to have a very challenging project.
Terri Kennedy
Experienced Member
At the LSSM, I had wrapped up work on a visit when Dave McGuire asked me to look at an 11/70 that was behaving strangely - front panel lights changing when the CPU was halted, Single Step going to random memory locations (when the instruction wasn't a branch), etc.
I said sure. I powered down the 11/70, pulled the card cage out, removed the TIG, gave it a dirty look, put it back in and said "it'll be fine now". And when powered on, it indeed worked fine (and still does to this day). Dave asked "What did you do?" and I replied "They're afraid of me". I think he half-believed me. Next week I'll actually be back at the LSSM working on that same 11/70, doing a "downgrade" to core memory. When that system was at its original customer site, it was on a FS contract and they upgraded it from core to MOS (and left all of the old MJ11 stuff intact) for free because they could never get the core to work reliably. To be period-accurate, it needs to have core.
On the third page of the engineering drawing of M8131, IRCA IR07 (1) H is connected to BK1 and BR1 in two places respectively.
I feel that there is a wrong mark in the drawing, can anyone confirm which pin should be connected actually?
On the same page, the pin13 of E20 is PDRD PS12 (1) H. The edge connector number of the connection is not clear from the engineering drawing, but it seems to be CB2. Could someone please help confirm it
I feel that there is a wrong mark in the drawing, can anyone confirm which pin should be connected actually?
On the same page, the pin13 of E20 is PDRD PS12 (1) H. The edge connector number of the connection is not clear from the engineering drawing, but it seems to be CB2. Could someone please help confirm it
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Terri Kennedy
Experienced Member
Circuit Schematic. I think they either removed a letter on the artwork starting from the beginning if they re-laid out the board, or ground off if they did the change by etch cuts and jumpers.