Viglen CRT monitor intermittent jumping
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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 .Comment
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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.Comment
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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 ?Comment
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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 farLast edited by R_J; 11-23-2018, 09:56 AM.Comment
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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 farComment
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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 themI 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.Last edited by R_J; 11-23-2018, 12:22 PM.Comment
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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 themI 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.
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.Last edited by roadrash; 11-23-2018, 02:25 PM.Comment
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Re: Viglen CRT monitor intermittent jumping
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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.Comment
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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.Comment
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