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Thread: VR201 Repair Opinions

  1. #1
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    Default VR201 Repair Opinions

    While working on my Rainbow, the screen started rolling vertically. It stopped after a while but the readout is now extremely faint tot he point only half of most characters are readable. (it's a monitor issue. I checked.)

    This particular amber phosphor VR201 seems to of been with the unit since it was sold back in '83. When I got it at first all I was dealing was cataracts and a slightly dim screen. With on and off use the screen got more and more dim until tonight. I can easily repair the cataracts however will I get more time out of the monitor if I gave it a recap? It seems odd it got so dim so fast.
    Last edited by NeXT; August 28th, 2013 at 10:40 PM.
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  2. #2
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    Next,

    I would doubt that it has to do with capacitors. There are number of things to check, but I'd start by finding the old-school TV repair guy in the neighborhood with a CRT checker/rejuvinator. If the tube checks out, next place to look is in the HV supply. I have never seen a VR201 fail by going dim, but perhaps yours has high hours on it.

    Of course, I would say you should fix it.

    Lou

  3. #3
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    Check the power supply in the monitor, you may have a week or dying filter capacitor and that’s giving you reduced voltage that will cause the vertical roll and reduced brightness. The HV and fly back never decrease output to the extent that when the fly back fails you get nothing at all. From what you describe its sounds like a power supply issue to me.

  4. #4
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    I'll talk to the guy at the local electronics shop today. Off hand I have both a flyback tester (Eico 944) that's too old for this application and a tube rejuvenator for the wrong make and size of tube.

    For future reference, it's a Philips M31-341LA CRT.

    Check the power supply in the monitor, you may have a week or dying filter capacitor and that’s giving you reduced voltage that will cause the vertical roll and reduced brightness. The HV and fly back never decrease output to the extent that when the fly back fails you get nothing at all. From what you describe its sounds like a power supply issue to me.
    That's what I was suspecting as well. Thing is that the monitor is powered over the video cable and I don't think that's a high voltage line so would it be better to suspect filter caps int he computer itself?
    Last edited by NeXT; August 29th, 2013 at 08:06 AM.
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  5. #5
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    The VR201 gets +12V from the connected terminal or computer. Somehow I totally missed the vertical roll problem and my mind only focused on the dim screen. Forget the CRT checker - Ray is right, it must be a power supply problem.

    Lou

  6. #6
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    Power supply problem as in the Rainbow itself or a secondary PSU circuit in the monitor?

    By the way. Cataract surgery was completed this afternoon.
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  7. #7
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    I think the power supply would be in the monitor, but you could check it by scoping the 12V output from the computer to the monitor while everything was powered up.

    The "mould" removal job looks fantastic! Great job there!

    Lou

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    This is all pure speculation being that I have not worked on that but would assume that the +12 volt supply to the monitor feeds the Horizontal stages only and all other voltages developed in the display are provided by additional windings on the fly back (Horz output transformer). The filter caps for that will be smaller than the usual AC power supply capacitors but will still be can electrolytic. Did not know there was no low voltage supply in the monitor itself. Still first rule of troubleshooting is check the power supply, try looking at the +12 volts input on the monitor itself.

  9. #9
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    +12v seemed okay out of the PSU so I went ahead and recapped what I could. The only cap I couldn't replace was a large grey 25V 10UF bipolar cap because I didn't have one. In all I replaced some 18 caps.
    The result was mixed.



    Brightness control funky. This photo was taken with the brightness and G2 pot cranked down as low as it could go and the screen was stills so bright it was putting it out of focus and displaying a raster. You can turn up the brightness until the screen is a blindingly bright orange lamp. I'm not smelling anything and nothing's exploded so I don't think I put a cap in backwards.

    Edited: I did put ONE cap in backwards it seems however reversing it did not rectify the issue.
    Last edited by NeXT; August 30th, 2013 at 07:38 PM.
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  10. #10
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    There was another reversed capacitor. 10uf 250V.

    Most of the caps I replaced were axials and radials were cheaper so I ran into problems several times where the older caps eiher had incorrectly marked polarity on the board or the cap itself was indicating the positive side, not the negative like we expect.





    After final adjustments the screen is still a little dim but for its age that's more than enough for me and probably more related to the age of the tube.

    The capacitors that were replaced are as follows:

    5 - 25v 100uf
    4 - 50v 50uf
    4 - 16v 1000uf
    3 - 16v 470uf
    1 - 30v 47uf
    1 - 250v 10uf
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