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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

2 years, 2 months

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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

2 years, 2 months

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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

2 years, 2 months

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Shelves / Rails for DEC Racks Questions

by Jay Jaeger

I have some open slots in some of my racks. I do have some old DEC rails, but I have a fair amount of equipment, from both DEC and other manufacturers, for which those rails are not suitable. Does anyone have any specific recommendations for shelving? (where equipment could just be slid on top of, if the equipment isn't too wide - some pieces are very close to 19 inches all by themselves, and were designed for front cantilever style mounting.) Would also be interested in specific recommendations for the following: DEC VR14 (I have one on a PDP-12 with proper rails, but have another to mount and don't have proper rails for it) HP 88780 (Perhaps a shelf is the best bet for these?) JRJ

2 years, 2 months

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VCF Swap Meet - Wall, NJ - Oct. 28, 2023

by Jeffrey Brace

Same place as last year in the big parking lot across from Brookdale and down the street from InfoAge Science and History Museums. We have Southern Monmouth County Firehouse museum selling food and drinks in the middle. This is a fundraiser for both museums (VCF and Firehouse museum) which are both part of InfoAge. All the info is here: https://vcfed.org/vcf-swap-meet/ Thanks! Jeff Brace VCF National Board Member Chairman & Vice President Vintage Computer Festival East Showrunner VCF Mid-Atlantic Event Manager Vintage Computer Federation is a 501c3 charity https://vcfed.org/ <http://www.vcfed.org/> jeffrey(a)vcfed.org

2 years, 2 months

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Re: Free Fujitsu M2444 6250 BPI tape drive

by Len Shustek

The drive is saved from the landfill! It was picked up by a classic computing fan at noon this morning. (And yes, it is Pertec-compatible.)

2 years, 2 months

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Theory of operation of DEC H7441 regulator?

by Tom Hunter

The DEC H7441 regulator is a relatively complex circuit using 2 x 555 timers, 2 x LM301 op-amps, 2 x transformers and 2 inductors I am struggling to understand how it is meant to work and was hoping to find a maintenance manual for it. Could anyone with such a manual please help? Alternatively is there another explanation of the operation of this or similar types of circuits? The circuit implements a switch mode supply. One of the two 555 timers operates as an oscillator, the second I think operates as a monoflop with the pulse length controlled via one of the LM301s. Overall the circuit seems very complex and while I understand parts of it, other parts are mysterious. In particular the top left section around Q1/Q2/Q3 and T1/T2 and E3 is most confusing. I did not find anything remotely similar in "The Art of Electronics" from Horowitz & Winfield. The H7441 schematics are available from here: https://deramp.com/downloads/mfe_archive/011-Digital%20Equipment%20Corporat… Thanks for any help or suggested reading material. Tom

2 years, 2 months

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Free Fujitsu M2444 6250 BPI tape drive

by Len Shustek

I bought this giant GCR tape drive on eBay five years ago, http://www.bitsavers.org/pdf/fujitsu/_brochures/M244X_Brochure_1984.pdf hoping to be able to use it to extract analog signals from 6250 BPI tapes to feed into my decoding program. https://github.com/LenShustek/readtape I failed to figure out how to get the right signals out, and eventually abandoned the project. I now need the space it takes, so I'm offering it for free before consigning it to the landfill. It's big (20" x 24" x 30" on the wheeled stand I built) and heavy (160 lbs) so I won't ship it. Pickup only, on the San Francisco peninsula.

2 years, 2 months

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DEC VT36 Color Graphics Display Control System

by Hans-Ulrich Hölscher

Hi, who knows details about the DEC VT36 Color Graphics Display Control System ( https://classic.technology/vt36-color-graphics-display-control-system/)? I'm looking for manuals for the VT36 as well as for the associated VAX-11/PROVUE or RSX-11/PROVUE software. Anyone with personal experience with the VT36 and/or PROVUE? Ulli

2 years, 2 months

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Re: Vintage Computer Systems for sale

by Stephen Pereira

Sorry Sellam, none of the websites I mentioned for information are mine. smp - - - Stephen Pereira Bedford, NH 03110 KB1SXE

2 years, 2 months

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