test-drb July 2020

test-drb@ccmp.vtda.org

148 participants
104 discussions

Fan problem with DEC H7822 power supply in MicroVAX 3100

by cctalk＠beyondthepale.ie

I have a MicroVAX 3100 which has a H7822 power supply. The power supply and the machine itself mostly work (there is a problem with the SCSI interfaces but that's another story) except that the two fans in the power supply don't run. If left on for a long time, the machine gets too hot and a thermal trip operates, shutting it down. The fans are DC 12V 0.2A and if I connect them to +5V or +12V, they work fine and don't draw excessive current so there would seem to be a problem with the section of the power supply which drives the fans. Unfortunately, it's operation is not obvious and the power supply is a pig to work on. It consists of two double sided PCBs connected by short leads and having live parts on both boards making it difficult to get access to both sides of the board where the fan circuit is when the power is on. I don't have an identical working power supply to compare the faulty one to but the fan circuit looks superficially similar to the one in the H7821 which I do have working examples of so that may be a way to proceed. Does anyone have a service manual for the H7822 or H7821 or know how the fan circuit is supposed to work in these power supplies? Regards, Peter Coghlan.

4 years, 5 months

Anyone out there that can read 7 track / 556 BPI tapes?

by cramcram＠gmail.com

Hi, I bumped into an old friend of mine today. We both talked about a pair of machines we worked on that no longer exist as far as we cant tell. They were both Adage machines and had the same base digital architecture. Their names are Ambilog 200 and AGT-30. The Ambilog was the predecessor to the AGT line. The AGT came in 3 flavors, AGT-10, AGT-30 and AGT-50. The 30 seems to have been the most prevalent. They were 30 bit, one's complement machines. The Ambilog had a beautiful console that used an IO Selectric. It was designed as a 2D vector graphics machine. Here's an image of the Ambilog 200: Ambilog 200 <https://d.lib.ncsu.edu/collections/catalog/ua023_024-001-bx0010-020-004#?c=…> The AGT/30 was a very advanced 3D vector machine. The XYZ signals for the display came from a 4 x 3 "hybrid" matrix multiplier which allowed for 3D imaging with Z axis depth cueing. The matrix multiplier was a 19 in rack of a dozen discrete 15 bit multiplying D to A converters. About once a year it had to be re-calibrated due to long term drift. Here's a link to an image of an AGT-30: Adage AGT-30 <https://www.google.com/url?sa=i&url=http%3A%2F%2Fwhat-when-how.com%2FTutori…> And here is it's 1.5 seconds of fame from the SciFi classic "Dark Star": AGT-30 das Blinkenlights <https://youtu.be/ocse-0bBfo8?t=3152> Anyway, it turns out he has quite a few of the source and backup tapes. Unfortunately they are 7 track 556 BPI. So the question is: is there anyone out there that can assist with either reading these tapes or (better yet) has a 7 track tape head we could buy? Our goal is to preserve this forgotten machine designed at the start of the computer graphics era. Writing a full emulator is our goal. I live in the Bay Area. Maybe those of you with connections to CHM could see if we could read the tapes on the 1401. Or maybe one of you has a 7 track driver in your junk file. All we really would need is the head and we could put it on an existing drive. As a last option, a commercial tape recovery vendor although that is probably too pricey. Thanks, Marc Howard

4 years, 5 months

Motorola 12Xbug?

by cmhanson＠eschatologist.net

Does anyone know where to find Motorola 120bug or 12Xbug? I have an MVME121 but it has a third party ROM, not the typical Motorola boot ROM. (The 12Xbug manual would be handy too, of course.) -- Chris

4 years, 5 months

MVME225 documentation

by cmhanson＠eschatologist.net

Does anyone have MVME225 documentation? I have one of these boards now and no docs for how to set the addressing jumpers/switches. -- Chris

4 years, 5 months

When is a capacitor not JUST a capacitor (i.e., not just a filter or part of a resonant circuit)

by cube1＠charter.net

(And not acting as part of a resonant circuit) Answer: When it is acting like a little delay line. https://www.computercollection.net/index.php/2020/07/18/q-when-is-a-capacit…

4 years, 5 months

Help identifying mystery Dataram VAX-11/750 (?) board

by derschjo＠gmail.com

Hi all -- Picked up a board advertised as a "4mb memory board" for a VAX-11/750. It's made by Dataram and I'm unsure of the model number, based on photos of it. I just noticed that rather than being a hex-height board that goes in the memory backplane, it looks like a board that goes in the main CMI backplane. It also appears to have 16mb of ECC memory on it, rather than 4mb. My thought is either (1) it's not actually for an 11/750 (in which case I'm curious what it would go into), or (2) it completely replaces the memory controller and standard memory and gives you 16mb in the 750. (Or it could be that it's something else entirely.) If anyone has any ideas or has a source of information, let me know. I put up a few pictures here: http://yahozna.dyndns.org/scratch/dataram/ Thanks as always, - Josh

4 years, 5 months

Compaq Smart Array 3200 Controller as a SCSI Controller

by cctalk＠gtaylor.tnetconsulting.net

On 7/17/20 7:07 PM, Paul Koning wrote: > Yes, if you define it that way then clearly I agree. The thing is > that in most people's definition, "drive failure" means "the drive > is a door stop". Ya.... I've had too many "but the drive isn't a brick ... how could it be the failure" experiences to use that as my benchmark. Now, if the drive is not doing what it's supposed to do in any (reproducible) manner, I consider it a failure. Well ... almost any reproducible manner. > And in fact, hard read errors are normal. Every drive has a spec for > the probability of that happening, and given the per-sector failure > probability and the sector count, the probability of SOME sector > failing to read when you read the whole drive is nowadays somewhere > around 1. Ya. That's where the reproducibility of any given failure comes into play. -- Grant. . . . unix || die

4 years, 5 months

Small C ver 1.00 source?

by wrcooke＠wrcooke.net

I'm trying to find source files for the very first, original, ver 1.00(?) small C compiler. I have the DDJ issue with the printed source (minus the assembly language runtime libs.) I have found all sorts of derivative works, but I haven't found files of the original version. My old eyes aren't up to typing in 13 pages of scanned copy of printed dot matrix listings. Does anyone know where a downloadable copy of these files can be found? Or have a copy they could send? Thanks, Will "A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." -- Antoine de Saint-Exupery "The names of global variables should start with // " -- https://isocpp.org

4 years, 5 months

interfacing DSI NC 2400 tape reader/punch

by billdegnan＠gmail.com

Is there a trick to archiving tapes to PC using Teraterm from a DSI NC 2400 reader/punch? Or is there a best software for this? From the terminal I can ctrl+Q to cause the reader to initiate a read of a test tape but I can't capture the output of the tape through the modem port of the reader into the serial port of my PC. I tried various things with settings. I was told it uses hardware flow control. The reader is set correctly as far as I can tell. I am using 2400/8/n/1 but I have tried other settings. I get no response from the terminal inbound at all. I am using a USB to serial interface that I know works with an RS232 modem, but it may not work with the reader. If so, I'd like to know if anyone has a similar experience. It may not be straight forward and I have to make a custom cable. I will keep at it, report if I find the answers. Bill

4 years, 5 months

100p Cables

by grumpyx＠gmail.com

I ran across some 50 POS 100 C/L card edge ribbon cables 9.5' in length, AMP 1-583717-9 connectors on each end. It's 2 x 50 pin cables between the connectors. https://drive.google.com/drive/folders/1rjGLewB3J4fDJc5cTRgDwInAVjWz2dxx?us… Any good uses for such a cable? Anyone in need of some?

4 years, 5 months

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test-drb July 2020