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Viglen CRT monitor intermittent jumping

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    Re: Viglen CRT monitor intermittent jumping

    Originally posted by R_J View Post
    I thought that was the problem. oh well onward and upward.
    Near the brightness control is a transistor marked Q212 check its voltages and see if they change when the brightness control is varied. that transistor conects to a wire at (C1) near q204 and I think goes to (C2)the area of the G1 voltage.
    The brightness control should vary that -63 volts if I am correct
    Oh so this is all corrent then and the problem is somewhere else. So it means more work yet. Sorry about all this and thanks for all your doing RJ.

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      Re: Viglen CRT monitor intermittent jumping

      if i am thinking about this correctly maybe a suitable signal could be injected to fire a gun then work backwards to where signals are lost .

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        Re: Viglen CRT monitor intermittent jumping

        It could be that the G1 voltage is too high cutting of the tube resulting in no video.
        You already confirmed there is video at the rgb inputs of the neck board, you could check what the video level is at the drive transistors (q802,q803 etc.)
        When there was a short in the area of g1 supply, that may have shorted the brightness control transistor and now it is feeding the full -63 volts to the crt G1

        Can you tell me where the wire going from the neck board (G1) goes to the main board ?
        Last edited by R_J; 11-22-2018, 06:24 PM.

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          Re: Viglen CRT monitor intermittent jumping

          Originally posted by R_J View Post
          It could be that the G1 voltage is too high cutting of the tube resulting in no video.
          You already confirmed there is video at the rgb inputs of the neck board, you could check what the video level is at the drive transistors (q802,q803 etc.)
          When there was a short in the area of g1 supply, that may have shorted the brightness control transistor and now it is feeding the full -63 volts to the crt G1

          Can you tell me where the wire going from the neck board (G1) goes to the main board ?
          Where the G1 wire is on the pcb can be seen in the attached picture marked in RED (zoom in) Near to HT transormer. I checked voltage at Q212 & it has vey little. 0v on the centre pin and 0.1v on the outer pins.
          Attached Files

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            Re: Viglen CRT monitor intermittent jumping

            I think we are getting somewhere, there is a transistor near the flyback that is connected with a wire from the brightness control circuit. There must be something in that area that is bad. transistors don't work too well with .1 volts on them
            Due to the wires etc. around the flyback I can't see how things are connected in that area, this is my best guess, so far
            Attached Files
            Last edited by R_J; 11-23-2018, 09:56 AM.

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              Re: Viglen CRT monitor intermittent jumping

              Originally posted by R_J View Post
              I think we are getting somewhere, there is a transistor near the flyback that is connected with a wire from the brightness control circuit. There must be something in that area that is bad. transistors don't work too well with .1 volts on them
              Due to the wires etc. around the flyback I can't see how things are connected in that area, this is my best guess, so far
              Here is a picture I took in that area and there are 2 trasistors there. One right aty the back Q203 and Q308 forward of it. Does this help?
              Attached Files

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                Re: Viglen CRT monitor intermittent jumping

                Yes it does, now if I could only get my meter leads in there to check them I would check Q203 first
                Q308 seems to be part of a different circuit,

                The G1 voltage does not seem to be controlled and is feed straight to the crt neck board. That Q203 circuit could be the ABL circuit (automatic beam limiter)
                There are 2 components I can't see, likely a diode and disc cap.
                Attached Files
                Last edited by R_J; 11-23-2018, 12:22 PM.

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                  Re: Viglen CRT monitor intermittent jumping

                  Originally posted by R_J View Post
                  Yes it does, now if I could only get my meter leads in there to check them I would check Q203 first
                  Q308 seems to be part of a different circuit,

                  The G1 voltage does not seem to be controlled and is feed straight to the crt neck board. That Q203 circuit could be the ABL circuit (automatic beam limiter)
                  There are 2 components I can't see, likely a diode and disc cap.
                  Q203 is a LC245P and it appears its OK. Ive checked it on my tester and the multimeter.
                  I also checked the diode below it and it is ok too.

                  Do you want me to check all the components on the other side of that circuit? There are 7 or more transistors there with 4 in small metal cans.
                  Attached Files
                  Last edited by roadrash; 11-23-2018, 02:25 PM.

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                    Re: Viglen CRT monitor intermittent jumping

                    What about the 2 components I could not see? what are they ? they come straight from the flyback and go to Q203

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                      Re: Viglen CRT monitor intermittent jumping

                      Originally posted by R_J View Post
                      What about the 2 components I could not see? what are they ? they come straight from the flyback and go to Q203
                      Not sure but is looks like a couple of resistors and whatever that is next to R264 (a cap I believe not sure what type). See pictures here now electrolytic caps are not in the way you can see.
                      Attached Files

                      Comment


                        Re: Viglen CRT monitor intermittent jumping

                        Yes thats a cap, It will likely be ok, I would check the transistor, just check it in circuit to make sure its not shorted.
                        They take the small changes in voltage from the flyback, and apply it to that Q213 base and the collector varies the voltage over by the brightness control via the wire connected to C2.
                        If that part of the circuit is ok, I would check the transistors around the brightness and contrast controls, They should have some voltage on them that varies on the center pin of the control when the control is turned. that should vary the amplitude of the video signal.
                        It seems like the brightness is turned down to minimum thats why there is no video.
                        Last edited by R_J; 11-24-2018, 10:23 AM.

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                          Re: Viglen CRT monitor intermittent jumping

                          Whoopeee! Its working again. Donr ask me what I did but I put back all the bits I removed around the flyback like the electro cap & Q203 etc and for the hell of it I changed that 47uf for a 10v cap like was originally and finally I squirted some servisol into all the swiches and rotary controls (god they felt so much betetr afterwards) and I thought I better make sure its still working before testing the transistors by the Brightness control etc. So turned the pc on and then the monitor and Bingo! it came up straight away with a picture of a "GEM desktop". So it was showing gtaphics on the screen.
                          I dont know what to sayt RJ thats the second time you have got me out of trouble and Ive learned a lot too like not replacing to many caps in one go plus watch for magnetic attraction of cut offs to the flyback area of the pcb although not sure thats whats caused that. Pity were so far apart I'd be taking you down the bub for a few pints RJ. again thanks al lot. I have another very ancient tiny little Apricot monitor to do sometime but ive got one that works we can use for referenece. Thats another thread. Cheers RJ!
                          Last edited by roadrash; 11-24-2018, 12:48 PM.

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                            Re: Viglen CRT monitor intermittent jumping

                            I'm glad you have it working, and I'm glad I could help, I've repaired thousands of crt tv/monitors over the years but not too many lately.

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                              Re: Viglen CRT monitor intermittent jumping

                              Well ive still got loads of old crt monitors and a few crt portable tv's that are still used in the bedroms etc

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