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101090 discussions

Replacing the Flyback Transformer From My VAXmate

by robert.jarratt＠ntlworld.com

I am about as certain as I can be that the flyback transformer from my VAXmate monitor board has failed. I know this is probably impossible, but I am wondering if there is a way to find a more modern equivalent? How standardised are these things? I do see a lot that appear to have the same circular arrangement of the pins. The VAXmate one is a Tai-Ho TH-1802B and according the Technical Description has a primary voltage of +28V and produces auxiliary voltages as follows: +13.1kV @85uA max +950V @200uA +45V @75mA max -100V @1.2mA Regards Rob

6 years, 1 month

OSI floppy test program

by djg＠pdp8online.com

I and others were having some problems with our floppy drives. Since I couldn't find a diagnostic program for the Ohio Scientific I wrote one. http://www.pdp8online.com/osi/osi-floppy-test.shtml With some floppy testing info here http://www.pdp8online.com/osi/floppy-repair.shtml If you try it let me know how it goes.

6 years, 1 month

VAXStation 3200 RAM repair video (again)

by joezatarski＠gmail.com

I had to repair the RAM board in my VS3200/KA650 again, so I took video of the whole process (less about a whole day I lost troubleshooting a trace I nicked). Maybe some of you will find it interesting to watch. https://youtu.be/3LxTJIzow2k (tip: get through youtube videos faster by setting to double speed, etc. :)

6 years, 1 month

Fixing Dungeon on RSX 4.2

by cz＠alembic.crystel.com

So I'm working on fixing some old code here. Found my balticon gaming system disks from 1990 (yes, I used to drag a pdp11 and 4 terminals to Balticon and other cons for computer gaming) and dungeon works on the 4.0 RSX version I was using but when I try to run it on 4.2 I get an Error 4 at PC 162570. I tried recompiling: RSXCMP works fine and compiles all the modules however when I run TKB with the rsxbld I get a bunch of *DIAG* Segment (root3, rooms, etc) has address overflow: allocation deleted. What am I doing wrong today? The task builder file is: dungeon/cp/fp=d.odl/mp stack=384 libr=fcsres:ro asg=sy:1:2:3:4,TI:5,CO:6 Reading the docs I see: The Fortran-IV-Plus object time library must be merged into the system library (SYSLIB.OLB). Further, the library must be set up to invoke the short error text module ($SHORT) as the default. Task building with a separate object time library produces numerous errors; task building with a resident library or the normal error text module produces an oversize task image. This might be the problem, anyone remember how to put the short error text module into syslib.olb? Hm. Maybe it is. Hm.... C

6 years, 1 month

DEC TK50 common failures?

by mcr＠martin-reilly.com

I'm trying to bring a pdp-11/83 back to working order. Challenge right now is storage - I have RQDX3 and RD54 but the RD54 appears to be unserviceable (never goes ready) and TQK50 with a TK50 which never gets to a stage of allowing me to operate the handle to load a cartridge - the green LED doesn't come on, the red LED is solid for a short time after power applied but then flashes rapidly. I plan to go with an MFM emulator in place of the disk, but would like to get a TK50 working as I have a lot of old stuff I'd like to try reading off cartridges. I have a spare TK50 drive, which behaves exactly the same. The TQK50 LEDs suggest it passes diagnostics, and the boot menu recognises it and will attempt to boot from it before saying there is no such drive. I don't have a spare controller. There is a lot of very detailed documentation for the TQK50/TK50 as far as the electronics and interfacing is concerned but I haven't found much in the way of information about the mechanical side. Are there common failure modes for these drives when they've been stored for a long time? Last time they were powered up is probably close to 20 years ago. Without much in the way of test kit (I have multimeter but no scope) is there anything I might be able to check easily? Thanks, Martin

6 years, 1 month

VT52 is back in service!

by cz＠alembic.crystel.com

Well, I put the VT52 back together, tightened all the bolts, plugged it in, turned it on and enjoyed the silence. I can just barely hear the transformer hum but that's about it. Hooked it up to my PDT11/150, booted up RT11 and the display is perfectly crisp and clear. Ran space invaders to check it out, no bugs or errors and the screen updates perfectly. Glad I got this working again. I'll take a look at that transistor, I'm almost 100% positive the switching transistor is either leaking or going bad. Either way I'll order a transistor when I have some time and put it in eventually to see if it works. But to be honest the new regulator is a thousand times better than the original discrete logic system. So moral: If your VT52 goes nutty and the screen becomes a blur try checking all of the voltages. An errant -12v will make the screen unreadable at -15v and I'm guessing oddness on the other voltage levels will do similar things as well. And don't leave it on for days, that's probably what pushed the transistor over the edge, but I'm guessing it has been crummy for awhile which is why I heard all that noise in the high voltage circuit. I feel like I accomplished something today. Thanks everyone for the help and thoughts in getting this old girl to work again... CZ

6 years, 1 month

Replacing Power LED on MicroVAX 3100/95 Power Supply

by robert.jarratt＠ntlworld.com

In fixing my PSU I managed to break the leads to the LED on the front of the PSU, probably through metal fatigue. I seem to remember people saying it is quite difficult to replace these, mainly because you can't get them out without breaking the holder. Is that right? Has anyone done this successfully and have any tips? Are there any recommendations for a replacement? If I remember correctly the LEDs used in those days were not as bright as modern ones and a modern one would end up being much brighter because of the higher voltage maybe? Thanks Rob

6 years, 1 month

Monrobot : A trip down memory lane in the world of computers

by cisin＠xenosoft.com

A friend recently reminesced about the Monrobot, which we have discussed a little bit lately, . . . [Note: Unrelated to the Marilyn Monroebot on Futurama] ---------- Forwarded message ---------- Date: Wed, 13 May 2020 16:38:22 +0000 (UTC) Subject: A trip down memory lane in the world of computers (I probably have shared this with you in the past) from an email to another friend... My high school... Erasmus Hall High School in Brooklyn...?? ? listed as THE LARGEST PUBLIC HIGH SCHOOL IN THE WESTERN WORLD (I guess they were trying to exclude China and India at the time) was the first in NY City to get its own computer... in 1965.?? ??IT was a Monrobot XI 2000. Regarding that Monrobot XI?? 2000...?? ?? ??made by the Monroe desktop calculator company of that era... Its main memory was a rotating magnetic drum, with 2K?? 16 bit words of fast electronic storage.?? Cycle op time was 11 milliseconds.?? It used 16 bit words, and one wrote its machine language using what was NOT called "Hexadecimal", but instead "Sexadecimal" (Latin, not Greek prefix was used)?? numbers, and NOT 1-9 then A-F, but rather 1-9 and then T-X.?? Storage was on punched paper tape. I learned to program it so that I could optimize access to the rotating drum memory and get three accesses (the max possible) per revolution of the drum, as much as tripling memory access speed. 11 milliseconds means?? 100 cycles per second.?? ??Modern desktop PCs operate at around 3,000,000,000 cycles per second.Compared to the 2,000 words of main system memory of the Monrobot XI, today's desktop PCs have around 8 to 32 billion words of memory. I programmed it?? (at age 14, in 1965) in machine language (the computer teacher didn't know how to do that)?? ... wrote a program for it to allow me to input and it to output to its printer a sequence of 3 strip tease images I got from a printout at Columbia University where I was then going to the Science Honors Program for high school kids, there. on weekends. ---------- Forwarded message ---------- I may be wrong about Erasmus Hall High School of Brooklyn being THE first high school in NY City to get its own computer. There is a reference elsewhere to Bronx High School of Science kids being taught IBM 650 language in 1959 or so. I suppose, if so, I could start splitting hairs and say that, while the Monrobot XI and the IBM 650 were similar in many ways, the Monrobot XI was a much more modern generation in that it used solid state, where the IBM 650 used vacuum tubes. I vaguely recall there may have been a Monrobot XI and a Monrobot XI 2000, the latter having twice the system memory (rotating magnetic drum) as the earlier model. Those were the days. I recall boot-strapping in programs in machine language from the front panel! I loved that machine. I remember the delicious smell of the high quality oiled paper tape! [Some paper tape was oil impregnated, some was not). The thing came with a Fortran compiler. You loaded your source tape on one tape reader, then loaded in part 1 of the compiler, and an intermediate tape was output. Then you loaded that intermediate tape and part 2 of the compiler on the tape reader, and a compiled program paper tape was output. THEN you input the compiled program, and (if you were very very lucky), it ran. Everyone else including the teacher used Fortran ONLY. I did most of my programming on it in machine (not assembly... I hand assembled my programs) ... machine language. 15 years later I programmed a prototype "Bio-medical micro computer" that incorporated the JUST MONTHS EARLIER released Intel 8080 processor to examine electrocardiograms in real time (interrupt driven) and identify abnormal beats. I programmed it in machine language, too. Storing programs in 1702 EPROMs. Input was via 3 buttons cycling 7 segment LEDs, and a LOAD and RUN button. And an analog input for the EKG signal. Output was to EPROM programmer and to EKG strip chart. Damn thing actually worked, pretty much. As well as most other efforts back in 1975, anwyay. ---marty

6 years, 1 month

Great, my VT52 is shot.

by cz＠alembic.crystel.com

Wonderful: A few weeks ago I forgot to turn off my VT52 and left it running for a day or two. Now the screen is filled with snow and it looks like the text is all over the place horozontally. Any tips or thoughts on where to start looking to fix? The keyboard seems to be working as does the RS232 input (the snow on the screen changes when the pdp11 talks to it) Thanks! Chris

6 years, 1 month

PDF of FANUC TAPE READER A860-0056-T020 Manual Wtd.

by billdegnan＠gmail.com

Turns out the "The Director" tape reader I purchased last week was defective and I got a refund. So I thought I'd try my hand at the FANUC TAPE READER A860. I may need to make a serial cable (?) to connect from the internal connector don't know yet. Or maybe the internal 50-pin port >from the photos is for the punch. Don't know yet, thus the need for the manual. I checked bitsavers.org but there was no manual there, anyone here have a PDF or URL of the PDF for the FACIT tape reader A860-0056-T020? Thanks in advance. Bill Degnan

6 years, 1 month

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