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Thread: DECWriter III Oddity

  1. #1

    Default DECWriter III Oddity

    Hello,

    Last week I picked picked up a lot of old DEC equipment from an estate sale. Along with a PDP 11/73 and a MicroVax II, I also got a DECWriter III.

    IMG_0184.jpg

    I brought it home and powered on, the fan spun up and it buzzed like my functional DECWriter II does, but no lights come up on the console, and the print head does not position itself to the edge of the paper. After looking at my unit some more, the keyboard does appears to be the same one used on some models of the DECWriter II LA36, and not the DECWriter III LA120. Furthermore, the internals of the DECWriter do not look a thing like the internals of other DECWriter IIIs I saw online. One of the boards was labeled "LA36", and had a plug that was not plugged in. I thought that the plug may had come loose but there is no loose power cable in the unit.

    IMG_0188.jpgIMG_0189.jpg

    I'm really not sure what to make of this, was there some sort of downgrade mod available for the LA120? Also is that board suppose to be unplugged? This is my first time getting real DEC equipment, and honestly I don't know a whole lot about it.

    Thank You.

    Additional Pictures:

    IMG_0185.jpgIMG_0186.jpgIMG_0187.jpgIMG_0190.jpgIMG_0191.jpgIMG_0192.jpgIMG_0193.jpgIMG_0194.jpgIMG_0195.jpg

  2. #2
    Join Date
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    Salt Lake City, UT, USA
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    Just going from the keyboard, this looks like an LA36, not an LA120. The LA120 had a VT100 like keyboard with a SETUP key and LEDs indicating various things. The LA36 has that group of keys on the left to configure baud rate, etc., as shown on yours.

    Compare DEC LA120 and DEC LA36 on the terminals wiki.

  3. #3

    Default

    If/when you go looking for parts, keep in mind that Teletype sold a ton of Decwriter III's rebadged as Tp1000's to all of the various parts of what used to be The Bell System. Surplus resellers might not have them cross referenced so search for both.
    "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

  4. #4

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    Quick Question: What is the different between a LA-120 and a LS-120? The back of my unit is label "LS-120" but I can't find very much information about it.

  5. #5
    Join Date
    Apr 2011
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    From the Fall 1978 DEC Sales catalog. There are 5 pages on the LS120 and accessories, this is the first.
    DEC_LS_120_DECwriter_III_01.jpg

  6. #6

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    Quote Originally Posted by ThisPostContainsComputers View Post
    Hello,

    Last week I picked picked up a lot of old DEC equipment from an estate sale. Along with a PDP 11/73 and a MicroVax II, I also got a DECWriter III.

    I brought it home and powered on, the fan spun up and it buzzed like my functional DECWriter II does, but no lights come up on the console, and the print head does not position itself to the edge of the paper.
    Did you try it with the cover closed? I seem to remember that my LA-120 would act dead if I powered it up when the lid was open.

  7. #7

    Default

    Quote Originally Posted by scott451 View Post
    Did you try it with the cover closed? I seem to remember that my LA-120 would act dead if I powered it up when the lid was open.
    I have tried to power it on both with the lid open and closed, but I can try checking the detector button and seeing if it is getting pressed.

    Also, having started trying to diagnose my issue, I have learned that the LA-120 and the LS-120 are decently different when it comes to internals and all the manuals for the LA-120 don't seem to apply. If anyone knows where I can find a LS-120 service manual that would be wonderful.

  8. #8
    Join Date
    Dec 2016
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    Helmond, The Netherlands
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    Default

    [QUOTE=ThisPostContainsComputers;528467]I have tried to power it on both with the lid open and closed, but I can try checking the detector button and seeing if it is getting pressed.

    And there is also a "paper out" microswitch.
    I will go to my "museum" tomorrow and have a look at my DECwriter II ...

    AFAIK, the DECwriter II was 30 char/sec, but the mechanics can handle higher speeds.
    There was an upgrade available to make it run at 120 char/sec (vague memories).

  9. #9
    Join Date
    Mar 2006
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    Salt Lake City, UT, USA
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    Quote Originally Posted by Henk View Post
    AFAIK, the DECwriter II was 30 char/sec, but the mechanics can handle higher speeds.
    There was an upgrade available to make it run at 120 char/sec (vague memories).
    The Selanar Graphics II board added graphics and higher printing speeds, but not 120 cps, only 50 cps. (Still a 66% improvement over 30 cps.)

  10. #10

    Default

    [QUOTE=Henk;529224]
    Quote Originally Posted by ThisPostContainsComputers View Post
    AFAIK, the DECwriter II was 30 char/sec, but the mechanics can handle higher speeds.
    There was an upgrade available to make it run at 120 char/sec (vague memories).
    The II's maximum rated print speed was 30 CPS, but it had a "catch-up speed" that was faster (60 CPS) to deal with the length of time it took the print head to return to column 1 after receiving a <CR>. There were a number of simple hacks around to get it to run at the 60CPS speed all of the time, but if you did that you needed a terminal driver that could pad <CR> with a bunch of <NUL> or it would try to start printing before the head got back to column 1.

    The Datasouth DS120 was the replacement board that let the LA36 print at up to 165CPS, with a boatload of other features (bidirectional print, APL character set, etc.). It pushed the mechanicals in the LA36 to the limit, though - one of the weak points was the carriage drive motor (specifically the optical encoder on the back side). I had a number of phone calls with the owner (nice fellow named Jim Busby) back when they were small enough to be able to do that. They eventually released a whole printer of their own design, the DS180, which was famously reliable. Then they introduced the DS220, which was famously unreliable. I had to call Jim and ask him to authorize a return-for-refund of all of our DS220s, unfortunately. These days, he apparently sells real estate in North Carolina.

    DEC was not without their own "difficult second album" problems - the DEC LA34 DECwriter IV was a real disappointment to those unfortunate enough to have encountered one after using a LA120 DECwriter III.

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