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Old 7th Oct 2005, 2:28 pm   #1
DoctorWho
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Default Marconiphone VRC52A Picture Fault

I'm looking for some advice if anyone can help please?

Some time back forum members kindly helped me with the restoration of my Marconi VRC52A console TV set. The set was in perfect working order.

This morning I turned the set on and it worked perfectly. It was switched off and switched back on a few hours later. There is now a picture fault in that the picture cannot be stabilised either horizontally or vertically. The picture rolls from left to right, then it will breifly stabilise and will then roll right to left, it continues to do this in one direction and then the other. The frame hold is also not spot on now and cannot be locked, but I suspect this is being caused by this fault. The sound is perfect and the picture detail can be seen but cannot be stabilised. The CRT is properly filled by the picture and has a good sized raster without distortion, the picture just will not remain still.

Can anyone suggest what may be the problem here please? Is it likely to be a valve needing replacement (perhaps the KT44?) or should I be looking for something else?

Any help with this would be greatly appreciated.

Many thanks,

Peter.
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Old 7th Oct 2005, 2:39 pm   #2
oldeurope
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Default Re: Marconiphone VRC52A Picture Fault

Quote:
Originally Posted by DoctorWho
The picture rolls from left to right, then it will breifly stabilise and will then roll right to left, it continues to do this in one direction and then the other..
feature box

Please show us a screenshot. Maybe your sync is missing and I don't
understand your discription

Kind regards
Darius
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Old 7th Oct 2005, 4:55 pm   #3
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Default Re: Marconiphone VRC52A Picture Fault

Thanks for your help Darius. I've attached a screen shot.

You may well be right about sync pulses, if so, how do I go about tracking this fault?

Any suggestions greatly appreciated.

Peter.
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Old 7th Oct 2005, 7:35 pm   #4
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Default Re: Marconiphone VRC52A Picture Fault

Peter,
The sync seperator valve in your VC52Da is V10. This is type Z66 and could be faulty but you will have to check the resisitors connected to pins 3 [anode] and 4 [screen grid. R43 is 47K and R44 is 100K. [HMV 1805 circuit]
The KT44 is the line output valve and will not cause your problem. There is a 'snap connector' connecting the sync output from the video amplifier V6, another Z66. It connects to the top end of C31. Check to make sure this is still in place. My bet is R43 0r R44. Try swapping over the Z66's. If you loose the picture you will know that the sync seperator is faulty. As an emergency test, you could try an EF39 or 6K7 in place of the Z66. Thats a starter for now! The anode should read between 25 and 65 volts and the screen 90 to 140. If the resistors are faulty, one of the readings will be almost nil. WATCH THE MAINS EHT and don't snap the neck off the tube if the chassis slips and pulls the tube base wires...Best to pull the base connector off while you do your tests. Peter, Try to find as many PRACTICAL TELEVISION magazines from the 50's as you can get your hands on. There are many articles explaining the stages of a television receiver from a starters angle. SERVICING TELEVISION RECEIVERS by SPREADBURY is essential reading if you want to service these old sets. Regards JOHN.

Last edited by Heatercathodeshort; 7th Oct 2005 at 7:40 pm.
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Old 8th Oct 2005, 1:43 pm   #5
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Default Re: Marconiphone VRC52A Picture Fault

You were right John, R44 had gone open circuit, I replaced it and away the set went. Many thanks for your help with this.

When something like this happens would you tend to replace all of the resistors in the set to prevent such failure in the future, or would you just replace a faulty one like this?

Thanks again,

Peter.
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