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VT100: Failing 2114 Chip Replaced With One With The Same Fault

by Rob Jarratt

I posted recently that I had identified a faulty RAM chip in my VT100 and having replaced it the terminal seemed to get further into the self test. After further analysis with the logic analyser I have realised that it is still failing the RAM test, despite an apparent change in behaviour. I think the change in behaviour could be simply due to the slightly suspect keyboard cable. But here is the puzzle. When I first identified the faulty RAM chip if found that address 0x2408 would read back as 0x0A instead of 0xAA. I reckon this equates to E50 in the schematic, as it is the upper nibble of the second bank of RAM. I replaced the chip with one I bought recently. It turns out the self-test is still failing at the SAME address. I find this really hard to explain. It can't be the chip selection logic because then the addresses 0x2400-0x2407 would also fail and I checked the CS signal with the logic analyser just to be sure. I also checked the address lines directly on the RAM chip for any stuck bits and they seemed fine too. What are the chances of two 2114 chips failing at exactly the same address? Is there some failure mode I might not be considering? Thanks Rob

1 year, 1 month

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Re: How were 32-bit minis built in the 70s/80?

by Geert Rolf

Quote: > I could be remembering incorrectly but I think the Gould PN6080 mini we had exclusively for third year > comp sci at Macquarie Uni in the mid/late 80s was 32-bit made up of AMD2900 family logic (2901 ALU's). Find attached two pages of the CPU drawings of a Concept 32/67 and PowerNode 6000. Here the AMD 2901s show up. You remembered correctly! Geert Rolf owner of a PowerNode 6040 -- see https://geerol.home.xs4all.nl/DownLoad/UTX-paper.pdf

1 year, 1 month

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What happened to the PDP-8 on ebay?

by Bill Degnan

There was a PDP-8 (rack straight 8 with asr33) that was on ebay that disappeared..anyone know if it was sold? I can't find it, maybe the seller pulled the auction to sell privately. Bill

1 year, 1 month

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GEAC

by Bill Gunshannon

Here's a question for all our Computer Museum curators. Have any of the old GEAC Library systems ever been salvaged and put into a museum? They were curious boxes and I think would make a nice addition to a collection. bill

1 year, 1 month

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Microcom S-64 8085 system

by Wouter de Waal

Hi all I re-discovered some eurocards I found in a box at a swapmeet long ago. It looks like a complete 8085 system. Lots of RAM, 2K EPROM, I/O, FDC. The strange thing is that the EPROM is mapped at F800, the code in there looks like 8085 code, and looks like it wants to live at F800. And there's RAM at 0000. The DIN41612 A/C 64 pin bus has provision for 16 bits data. Pics here http://retro.co.za/8085/Microcom/ Anyone maybe have more information on this? I'm curious. W

1 year, 1 month

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Soviet tube/transistor/IC spec source

by Shoppa, Tim

For those working with ex-Soviet equipment from the 60’s and 70’s here’s a remarkable resource: https://www.govinfo.gov/content/pkg/GOVPUB-C13-6925b02fb6dcaa88935be001eb55… I am astonished that I found it in this in the US National Bureau of Standards (today NIST) archives 😊 Tim N3QE

1 year, 1 month

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The World Wide Web

by Murray McCullough

30 years ago the World Wide Web came into public existence. It has enabled cctalk to flourish. Murray 🙂

1 year, 1 month

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Possible DC012 Control Chip Fault on a VT100

by Rob Jarratt

I have my faulty VT100 now passing the RAM test, but it is still not producing any output to the screen. Looking at the DC012 chip it seems to be permanently asserting the interrupt line and not generating any DMA HOLD REQUEST signals. It seems that all the clock inputs are running (DOT CLK, CHAR CLK, VERT RESET). Unless there are other clock inputs not shown on the schematic, I think this suggests that the DC012 is faulty. Does anyone know of any other reason why the DC012 might behave this way? Anyone have a spare DC012 chip? I have posted a bit more detail here: https://robs-old-computers.com/2023/10/01/vt100-ram-fault/ Thanks Rob

1 year, 1 month

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Re: Microcom S-64 8085 system

by Wouter de Waal

Hi Tony and all >It might have run CP/M (which will run on an 8080, and therefore on an >8085). That needs RAM at location 0000 [1]. I know of CP/M, I even used CP/M (on my Apple) but I did not know it needs RAM at 0000. That's kind of strange, since everything that ran CP/M (OK, everything -80) has vectors at 0. I guess there was a reason behind it. I see the CPU board has a jumper "F000/F800" so I guess it does something to map that address to 0 after reset. W

1 year, 1 month

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Documentary on the SKALA computer of Chernobyl Nuclear Power Plant

by Sellam Abraham

This is a pretty interesting documentary describing the computer (SKALA) that ran the Chernobyl nuclear complex. https://www.youtube.com/watch?v=ZbaptQh2AM4 Sellam

1 year, 1 month

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