test-drb

test-drb@ccmp.vtda.org

101090 discussions

by erik＠baigar.de

..not to forget, that the 400Hz equipment was readily available from powering aircraft on the ground before the engines take over. So although not cheap, they where cheaper than a custom design at an arbitrary new frequency

5 years, 1 month

PDP-8/I Negative-bus termination

by derschjo＠gmail.com

Hey all -- I cabled up the RF08 to my 8/I this evening and it's showing some very faint signs of life -- a DIML instruction appears to do the right thing. That's about it. Until this point I've never had any peripherals for my negibus systems (apart from teletypes), and it occurs to me that I have no idea if the bus needs to be terminated (and if so, with what). There are 6 slots in the RF08 backplane (D01-D06) for daisy-chaining to the next device, which is where I assume they'd go; the RF08 manual does not make it clear what this looks like or if it's actually required, and I've gone through the available PDP-8/I docs and I'm still at a loss. Can anyone with negibus experience point me in the right direction? Thanks, Josh

5 years, 1 month

IBM 4700 question

by h.j.stegeman＠hccnet.nl

Hi, Does anyone known which processor IBM used in the IBM 4701 ? Branch Controller (8? floppy disc) ? Regards Henk

5 years, 1 month

General Instruments Capacitive Keyboard Encoder

by pbirkel＠gmail.com

I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key switches. The basic design employs a GI encoder coupled to an 8039 MCU supplemented by a 2K EPROM and 74LS373 (used to latch the ROM address set >from Port A while Port A is then used to read data back from the ROM). The 8039 MCU drives a bit-banged serial interface. The PCB identifies itself as AMPEX on the coper foil, although the key switch mounting-plate actually has a "General Instruments Quality Accepted" sticker. The EPROM is labeled "3512663-03 Copyright 1983 AMPEX CORP". The GI encoder is a DIP-40 labeled as "321239007 M2406-054-02 GI 8233 CBU TAIWAN". I seek technical documentation for this IC. It evidently is not a relabeled simple variant of the documented AY-3-4592 as it does not multiplex the input side of the matrix (sense lines), there are fewer output data lines, and the power pins are non-standard (Vcc = pin 37; GND = pin 16). Reverse engineering identifies this M2406-054-02 as supporting an 8 column by 16 row (3 unused in my case) matrix plus 8 output data lines. I can identify analogs of several pins on the AY-3-4592. My interpretation of the pin uses is that the necessary key-scanning behavior is generated using the 8039 ALE line (pin 11) as the encoder clock input. Proper documentation for this IC would be nice to come by! Pointers and suggestions appreciated. Thank you, paul

5 years, 1 month

That VAXStation4000vlc 3W3 video connector

by athornton＠gmail.com

I assume it would be way too much to hope that HD BNC would fit it? Does anyone have a pointer to the actual physical dimensions of the itty-bitty BNC-ish connector in the video port of the VAXStation4000vlc? If I can get red, green, and blue out (assuming since there are only 3 connectors it's sync-on-green) I can put together a sync splitter and turn it into VGA. I have at least one decent multisync VGA monitor still, although none with the RGB BNC inputs. Adam

5 years, 1 month

IBM 1410 FPGA Implementation Update - new github repository

by michael.99.thompson＠gmail.com

> > Date: Sun, 2 May 2021 15:38:33 -0500 > From: Jay Jaeger <cube1 at charter.net> > Subject: IBM 1410 FPGA Implementation Update - new github repository > Message-ID: <68c06711-e563-f1bf-8abc-090793bed752 at charter.net> > > The last 12 months I have been pretty busy working on my 1410 in FPGA > project, and there is now more to share, though I have not done much > actual work since February - been too busy playing with other "toys". 8D > > JRJ > The RICM has a 1401 control panel. It would be pretty cool to mount your FPGA to the back of it and get it to blink the lights the right way. https://www.ricomputermuseum.org/Home/interesting_computer_items/ibm-contro… -- Michael Thompson

5 years, 1 month

920M - and also the Argus 200 / 700

by erik＠baigar.de

Hi Jos! > in the UK around 1960 the Argus 200 was developed to control the Bristol > Bloodhound anti-aircraft rocket. This computer was one of the very first > transistor-based control computers. Absolutely - in these days Ferranti and Elliott where competitors on the European market for defecne computing! Very funny, that they later merged and today the legacy of both is distributed in the BAe and Leonardo businesses ;-) There are quite interesting stories, on occasions when the two had to cooperate before merging and in the ELDO project mentioned in my video, the computer was from Elliotts whereas the inertial sensor was from Ferranti (https://youtu.be/v-gF5g0nnoE?t=363). > In Switzerland the Bloodhound was on duty?? until 1999 ! One of the sites, > once top secret,?? is now a museum, and well worth a visit. > Check out https://www.museums.ch/org/de/Bloodhound-Lenkwaffenstellung Definitively worth a visit! I am also into the Ferranti navigation systems >from the 1970ties (https://www.youtube.com/watch?v=-EQqfxiGgd8) and since years I am trying to find out, what architecture its 32 bit computer is. Here I booked an extensive special tour and the team on mount Gubel organized some experts to join the tour - although I learned that the INS computer is not related to the Argus series, the visit was AMAZING! Also great there to see the technology of the almost Mach3 missile from the 1950ties. Erik.

5 years, 1 month

RS64 on a PDP-8?

by jnc＠mercury.lcs.mit.edu

Is there a controller to attach an RS64 disk to a PDP-8? The only controller for the RS64I can find is the UNIBUS RC11. Thanks. Noel

5 years, 1 month

Cipher C995 manuals

by drb＠msu.edu

I have a recalcitrant Cipher C995 9track drive. Does anyone have manuals for this thing? It seems to be enough different from the M990 to matter. Thanks, De

5 years, 1 month

Sprague 2X.1-1000 filter capacitors and 854-B power control assembly

by ccth6600＠gmail.com

Unfortunately once again I am having trouble with Sprague 2X.1-1000 filter capacitors. The two filter caps on a Lab-8/e rack's 854-B power control assembly appear to occasionally leak to ground more than the 30 mA tolerated by my RCD. Mostly it trips the RCD when I power off the system, but sometimes it even trips the RCD with the system powered off. One of the two filter caps is permanently connected across mains power and earth coming from the cable (i.e. it is before the power switch). The exact same filter caps were also used inside the LAB-8/e computer?s power supply. Early on I replaced these with a small PCB with a bunch of male spade connectors and two Y class safety caps. The PCB was designed to replace two of the Sprague filter caps in the side-by-side configuration used inside the LAB-8/e?s power supply where it is also hidden from view. The PCB was designed by Malcolm Macleod in Melbourne/Australia who hit the same problem. I got the PCB manufactured in China from his design. The 854-B power control assembly has the two Sprague filter caps sitting on either end of the assembly ? far from each other. Also the can of the capacitors is exposed at the back and clearly visible so even a newly designed PCB with a single set of safety caps wouldn?t look great and also wouldn?t be stable because there are only two mounting holes. I cannot think of a neat solution to resolve this. I could try to find an electrician willing to wire me a non-RCD protected socket into my study, but I can?t quite warm to that idea. The RCD is an important safety feature. By law now all houses are required to have their AC wiring protected by 30 mA RCD circuit breakers so I likely would have to do this myself. The other option would be to make or buy two terminal blocks with male spade connectors and connect the female spade connectors to those rather than the Sprague connectors. I could then also wire in the 2 Y class safety caps or even forego the filtering. It would mean drilling new holes into the power control assembly. Chuck(G) in the vcfed DEC forum suggested pulling apart the old "bathtub" capacitors and replacing their guts with modern safety caps. The caps contain toxic and carcinogenic PCBs so I am less than enthusiastic about that idea. The capacitor's metal can is soldered together so trying to desolder it would heat the mineral oil containing the PCBs which would make them even more harmful. There is no point in trying to hunt for ?new? Sprague 2X.1-1000 because they would all be ancient and have the same leakage problem. Any thoughts, ideas or suggestions? Best regards Tom Hunter

5 years, 1 month

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