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Thread: TU60 TA8E / M8331 maindec and caps-8 questions

  1. #11

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    I wonder is these will work too...
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #12
    Join Date
    Mar 2008
    Location
    Westchester County, NY
    Posts
    1,301

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    Folks,

    Sorry for being offline for so long. We've been working on our move from the NYC area to the Washington DC area.

    Indeed Mattis is correct that OS/8 works with the TA8E/TU60 as a non-system device. However, that is not a problem for making a CAPS-8 system cassette. To use OS/8 to make a CAPS-8 bootable cassette, one does not use BUILD as they are used to. Instead, you simply copy the files to a cassette that has first been ZEROed. Your OS/8 system head should of course have the TA8E handler INSERTed, or I think one can use MCPIP (I did the former.)

    The sequence of the files to be put on the cassette to make it bootable is critical. The first file must be the secondary loader, then second is the monitor. The remaining file order is not important. The TA8E bootstrap (either the one fat-fingered/MI8E'd into memor or the OS/8 BOOT TA) will read the secondary loader in to memory, which will proceed to load the monitor in off the cassette.

    It is important that cassettes used have clear leaders and have a hole/notch in the top approriate for a datacassette. Most of my original DEC TU60K media is unreliable, however I have had some success with more modern cassettes. I saved the clear leaders and housings from old cassettes and re-packed them with new tape. I found BASF (pre-EMTEC spinoff) tape to be the most reliable, however, even some recent Memorex tape was OK.

    And here is my post to alt.sys.pdp8 from 13 years ago when I first got CAPS-8 running again : https://alt.sys.pdp8.narkive.com/2ud...-original-iron. You will see that I built the bootable cassette the hard way. Back then I had very little hardware and no OS/8.

    In a fit of insanity some years back, I tried "playing" a TU60 datacassette in an audio cassette deck and digitizing the audio. At an 11kHz sampling rate (monaural, of course), I converted the audio to a raw data file. I made a crazy Excel spreadsheet that could process one block of data at a time, decoding the audio file, using the writeups in the manuals. It read the header and even verified the checksum. If there was tape dropout, you could look at the plot of the audio file and recover the bits by eye. It really did work and could handle the fact that "playback" of a Philips Compact Cassette used for audio has a constant 1-7/8 IPS tape speed while the TU60 which has no capstan, moves at varying tape speed (and therefore bit rate) depending on how much tape is on the the takeup reel. I made it while preparing to recover CAPS-11 Basic source tapes (which we recovered OK on the real hardware!) I will look for this file in the coming weeks and send it to anyone who is intersted. Recall that I am a mechanical engineer, so some things are brute force.

    Lou
    Last edited by Lou - N2MIY; August 14th, 2019 at 05:31 PM.

  3. #13

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    Hi Lou,

    Quote Originally Posted by Lou - N2MIY View Post
    To use OS/8 to make a CAPS-8 bootable cassette, one does not use BUILD as they are used to. Instead, you simply copy the files to a cassette that has first been ZEROed.
    Thanks a lot for your info! That sounds quite easy to do. But I still think it would be very nice
    to have a DumpRest version for the TU60 too. You never know what interesting kinds of tapes show up in the future.

    Quote Originally Posted by Lou - N2MIY View Post
    Your OS/8 system head should of course have the TA8E handler INSERTed, or I think one can use MCPIP
    That was one of my questions in general. How to add devices in an existing system. Not only the TU60, but also the TU56, RX01 etc...
    I hope someone can point me into the right direction on that...

    Quote Originally Posted by Lou - N2MIY View Post
    The sequence of the files to be put on the cassette to make it bootable is critical. The first file must be the secondary loader, then second is the monitor. The remaining file order is not important.
    Are these files on the http://simh.trailing-edge.com/kits/caps8_all.zip file usable on real tape?
    I wonder which files I need to put on the tape. What are the filenames of the secondary loader and from the monitor?

    Thanks for your help here!

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  4. #14

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    Today I got my TA8E boards and I have build one of them.
    And I got it trough the static maindec test

    IMG_20190823_013206.jpg IMG_20190823_013215.jpg

    But at first I got a lot of errors of the A register. It turned out to be a bad 74179.
    And then I got these errors continue looping...

    PC=0312 KSEN SKIPPED
    PC=0322 KSAF SKIPPED

    Since there is no original maindec documentation I could not exactly find
    where 0312 and 0322 were in the code. But thanks to the work of R.Krten I
    could figure out that these errors were generated at IOT 2 and IOT 5.
    And in the code was mentioned that these tests were skipped in case of an error.

    The errors were coming from the circuit which checks for an empty drive, write lock etc...
    Then I found two typo errors in my schematic. A label was called EOT-BOT_H and at another place EOT_BOT_H.
    And the second was CRC-BLK_ERR_H instead of CRC_BLK_ERR_H. So I got two pins floating in my design.
    Normally I always copy labels to prevent these kind of errors. So I don't know why this went wrong...

    IMG_20190823_013337.jpg

    But hey, DEC used more wires on their original TA8E board. I will update the schematic drawing and PCB files off course.
    I don't like wires on my PCB. But I think it's very nice that I got this far. Before I can go further I need the rollers
    to be done first. I think I will sent them out to a factory like Terry's Rubber Rollers & Wheels

    I will put the schematic on my GitHub. PCB files will come later when I have updated them.

    In the meanwhile I'm going to focus on building a few VC8E clones and the M882 RTC.

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  5. #15
    Join Date
    Jul 2014
    Location
    Rhode Island
    Posts
    1,206

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    The RICM has a TU60 with melted rollers. Please post your results with getting the rollers replaced.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  6. #16

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    When I restored my TU60 I happened to find idler tires for a tape recorder which had the correct dimension. It worked very well!

  7. #17

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    Quote Originally Posted by MattisLind View Post
    When I restored my TU60 I happened to find idler tires for a tape recorder which had the correct dimension. It worked very well!
    Hi Mattis,

    That sounds great, do you know the size or order code of the ones you used?

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  8. #18

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    From both of the TU60 drives which I have here just one sensor light bulb was still working.
    I could not find the spec of the bulb in the documentation or about the HEI B10461A sensor.

    So I've done some measurements. The 'bulb ok' detector circuit takes about 1V of the 5V power.
    Dec often seems to use a bit lower voltage on bulbs to extend their lifetime. So I assumed the
    bulb would be a 5v or 6v model with a quite high power. The current that flows trough the bulb was
    around 100mA at 4V. So that would mean that I need a bulb of approximately 120mA at 5V or 150mA at 6V.

    After a bit of searching it seems to be a wire leaded T1 (3mm) bulb. I found a 5V 115mA model 715 incandescent lamp at Farnell.
    https://nl.farnell.com/cml-innovativ...75w/dp/1139298

    The sensor was quite easy to open. Now all sensors have new bulbs in it. They give the exact same
    brightness as the original. And the sensor output has also the exact same voltage levels.
    So that is done as well... Now back to the idler tires...

    TU60 old lamp out.jpg

    TU60 new lamp in.jpg

    IMG_20190826_213531.jpg

    To be continued...

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  9. #19

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    Roland,

    send me th exact dimensions you need for the roller, I will 3D print some for you.
    The ninjaflex flexible filament should be just right for the job.

    Jos

  10. #20

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    Hi Jos,

    Sounds like a nice experiment to me! The inner diameter is 35mm, outer diameter is 38.2mm and the height is 6mm.
    Probably a good idea to make the inner diameter 34.9 for a tight fit... Do you know if it's possible to glue the printed
    rubber on a surface? This to prevent slipping of the aluminum wheel.

    Thanks for your help!

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

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