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Thread: IBM 3191 terminal repair

  1. #1

    Default IBM 3191 terminal repair

    I thought I might share my efforts at establishing 3270 terminal communications with a Hercules emulated IBM 370 mainframe OS using real hardware.


    I started with the repair and rebuild of a IBM 3191 coax connected terminal aka 'green screen' that left the IBM factory in 1988. I somewhat rashly plugged this in after retrieving it from 20 years of storage and within a few minutes copious quantities of smoke came out. Most of it being burnt polypropylene but the smoke was also laced with tinges of the slightly tarter blown electrolytic smell.

    Now it today's health, safety, and litigious environment I need to plainly state that unless you are completely familiar with high voltage electronics don't try this at home. All CRT terminal use high voltages and the 3191 uses 12,000 volts to accelerate electrons towards the phosphor screen.

    After disassembly it was clear that the class X2 RIFA polypros had blown (these are almost mandatory to replace with old machines) and most of the electros too (most often happens in switched mode power supplies). Here is a shot of the power supply board on the bench with the dead caps set out on the right and the clean-up and repaired board on the right:

    All the dead capc.jpg

    The yellow electros left on the board were still OK but might need replacement in future.


    After putting the PSU board back in its metal case and mounting that back in the monitor, a quick bench test showed all the right voltages on the power supply plug:

    Putting PSU back together.jpg


    Then after some major cleaning effort on the case this was the result when testing against a 3174 controller:

    Result.jpg


    Result!

  2. #2
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    Well done!
    Torfinn

  3. #3
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    Quote Originally Posted by Kiwi View Post
    Then after some major cleaning effort on the case this was the result when testing against a 3174 controller:

    Result.jpg
    Result!

    good job!

    token ring or ethernet out of the 3174?

  4. #4

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    Token Ring into a Cisco 2612. Just battling with the floppy drives and media at the moment. I'd lke to replace the drive with a memory card but I need to get the images off the originals first.

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    Did you have any luck copying the floppies?
    I just got a 3174(-11?) w token ring and it still has a set of floppies in it
    I tried imaging them with a supercard pro, but nothing recognizable resulted.
    Will try again today.

    Also, there were several 3191s w kbds on eBay cheap, so I bought three of them.
    It appears we have no manuals at all for that model. Would it be possible for you
    to scan the setup or operators manuals? (assuming you have them)

  6. #6

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    I just attempted imaging a 3174 floppy recently as well. I used a raspberry pi and the bbc-fdc project (https://github.com/picosonic/bbc-fdc).
    It uses the SPI input on the pi to record an entire track at a time. I was able to get a capture of the flux trasitions (78 MB), but the program couldn't make sense of the data on it, implying these aren't normal MFM disks.

    This project also gave me the idea that it would be possible to build a raspberry pi based floppy emulator which can use these files directly, removing the need to decode the disks.

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    Quote Originally Posted by cfsimmons View Post
    This project also gave me the idea that it would be possible to build a raspberry pi based floppy emulator which can use these files directly, removing the need to decode the disks.
    Have you tried just writing what you read back to a disk to see if it can IML?
    I was just thinking it may be necessary to put a logic analyzer in line with the 2.4m floppy cable to see if any lines are asserted
    by the 3174 only in 2.4m mode and seeing what the read data looks like on a working IML

  8. #8

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    I haven’t considered the possibility that the drive has additional signals, that’s worth a look though.
    I think my next step is going to write my own c code for the raspberry pi which records only a single revolution of the disk. The project I’ve been using estimates the length of the buffer needed to record 3 revolutions, and fills that.
    Then I’d like to make a floppy emulator. From there I ought to be able to record how a data block is written, by only examining the write data signal.

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    Quote Originally Posted by cfsimmons View Post
    I haven’t considered the possibility that the drive has additional signals, that’s worth a look though.
    I think my next step is going to write my own c code for the raspberry pi which records only a single revolution of the disk. The project I’ve been using estimates the length of the buffer needed to record 3 revolutions, and fills that.
    Then I’d like to make a floppy emulator. From there I ought to be able to record how a data block is written, by only examining the write data signal.
    I would really encourage you to look at the Beaglebone instead, the work done by Dave Gesswein on the MFM emulator, measuring
    the time between transitions, and Ken Schriff building a 3 megabit to 10 megabit ethernet bridge.

    I had thought about using a DP8344 for the coax comms, but realized you should be able to do it with the PRU on the BB.

    https://github.com/dgesswein/mfm
    https://github.com/shirriff/alto-ethernet-interface

  10. #10

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    Quote Originally Posted by Al Kossow View Post
    Would it be possible for you
    to scan the setup or operators manuals? (assuming you have them)
    Sorry I have no manuals.

    The key issues for me is restoration of the floppy drives. But I've been on the road for a month no progress at the moment.

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