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Thread: DEC Terminal VT320 - broken tip of the tube

  1. #1

    Default DEC Terminal VT320 - broken tip of the tube

    Hi

    from another country arrived to me VT320 and it arrived broken - the display doesn't work and it makes strange sound.

    http://pmlabs.net/retro/vt320/IMG_1115.MOV

    I saw, that the tip of the tube is broken:



    Can this be fixed somehow?

    Best regards,
    Pawel

  2. #2
    Join Date
    Sep 2020
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    Perth in Western Australia
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    Hi Pawel,

    Sadly this cannot be fixed economically. In the past there used to be companies which refurbished CRT tubes but most of these are long gone. I am aware of one in the US which is still operational and repairs CRTs for the military but the prices are silly and only the government can afford it (they print their own money).

    You could try to find a replacement CRT tube, but it might be best (and cheaper) to find another VT320 and use this one for spare parts.

    Good luck with it.

    Tom Hunter

  3. #3

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    No, sadly it can't be fixed.
    But the VT320 can be saved, I have done a CRT transplant procedure in the past and posted a rough guide, you can check it out here:

    https://microvax2.org/wp/2017/05/24/...t-replacement/

    You'll need to find a donor monochrome CRT. All of the monochrome monitors of this size that I have seen so far had the exact CRT size, shape and connection, so finding one should not be too difficult or expensive.

    -Alon.

  4. #4
    Join Date
    Mar 2011
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    The Netherlands
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    The sound that you are hearing is EHT sparking probably inside that tube because it is not vacuum anymore. Swapping a CRT from a donor is not hard to do. But it is important that you pull of that board in a straight line from the CRT. Sometimes the connector is glued onto the CRT with a blob of glue. Just use a sharp knife to cut that before pulling it off. Otherwise it can end up with a SSSSsssss........ by breaking off that vacuum stem. Then you have another dead crt.

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

  5. #5

    Default

    Thank you guys for answers. I live in Poland and looking around for amber VT320 or VT420, but currently there are none. In the meantime, I ordered cheap VT420 from Germany (I hope it will arrive working), but it's green - I'm still dreaming on an amber terminal dough.

  6. #6
    Join Date
    Oct 2017
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    Kentucky USA
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    I bought two new tubes for my VT320's due to burn-in a few years ago for maybe $60 ea in the US from VDC or a subsidiary thereof. The job is unpleasant, but doable. I bought them because I thought they would be unobtainable in the future.

    I HATE changing these but sometimes you have to do it.

  7. #7
    Join Date
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    Rapid City, SD USA
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    It would be a difficult repair. The part that broke off is basically the last part of the production process. The vacuum is applied to that tube and once pumped down it is sealed by melting the glass. I suppose a really skilled glass blower could attach a new piece of tubing in the middle of the pins and then you could draw a new vacuum and then seal off the tube again.

    It is possible that the metals used in the grids and shields could oxidize and cause problems. I don't know if anything was done to prevent that during manufacture. I am guessing that extended exposure to the oxygen in the air will have a negative effect on the internals.

    Your best bet is to find another tube, either new (Slobs reply), new old stock, or one from another device. Unless there is a vacuum leak these should store essentially forever (hundreds of years at least) without any degradation.

    Good luck!
    Doug Ingraham
    2nd owner of Straight 8 SN1173
    5 other PDP-8's including an 8/i and a DECSet 8000
    SOL-20

  8. #8
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    Sep 2020
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    Perth in Western Australia
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    Here is a link with lots of interesting info about what is involved in rebuilding/refurbishing a CRT:

    https://www.earlytelevision.org/crt_rebuild.html

    Check out the various links from that web page!

    It shows that it is possible in principle, but not a trivial exercise. In fact it was a common procedure in the early days of CRT TVs where a TV was as expensive as your car and CRTs had shorter lives due to limitations of the technology at the time.
    You would be very hard pressed to find a company which still has the equipment and expertise to do this today. I know of one in the USA but the cost is prohibitive.

    As others have suggested your should be able to find a CRT of the same size and it is very likely to work.

    Best regards
    Tom Hunter

  9. #9
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    Hi Pawel,

    Here is a working VT-320 on Ebay in Australia:

    https://www.ebay.com.au/itm/264807042574

    This might work out cheaper than trying to fix/replace your broken CRT tube.

    Best regards
    Tom Hunter

  10. #10
    Join Date
    Mar 2011
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    The Netherlands
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    Quote Originally Posted by thunter0512 View Post
    You would be very hard pressed to find a company which still has the equipment and expertise to do this today.
    The last CRT rebuilder was RACS in France. They quitted a few years back.
    I knew them from my vintage television hobby. Rebuilding the really old CRT's was quite expensive.
    Especially the round colour CRT tubes... Luckily I have a spare CRT, because rebuilding is over.
    Pre war CRT's made of Pyrex were even more problematic because they had to melt two different
    glass types together. Because the base of the new gun assembly was not Pyrex.

    Philips K4.JPG

    But even in the case of your CRT, the cathode material is poisoned by oxygen and can't be reused.
    The electron gun is heated by induction in the production process and then the cathode becomes activated.
    I don't know the chemical background, but the process is irreversible and not repeatable.

    So just get another terminal and swap the CRT.

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

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