KB WV70 Picture fault. - UK Vintage Radio Repair and Restoration Discussion Forum

Aristocratinuse · 28th Mar 2016, 1:57 am

Any help would be greatly appreciated.

Jonster · 28th Mar 2016, 6:19 am

Looks like the line timebase is running at half speed, could be a leaky capacitor or a resistor that has gone high in value in the line oscillator stage.

Nuvistor · 28th Mar 2016, 7:46 am

Is the 625/405 line time base switch in tbe wrong position?

slidertogrid · 28th Mar 2016, 9:56 am

Hi, Also check the line oscillator coil, the windings had a habit of dropping down the former. Sometimes someone would twiddle the core to get the frequency right again. This is ok unless the windings continue to sag enough to short the coil out.
I have only seen this happen on the early VC series chassis but it's worth a check, if you note the core position before you move it (so as it can be returned to its original position) you could try adjusting the coil to see if it will bring the picture in to lock. Only use an insulated trim tool here though a screwdriver will break the slug.
Failing that as others have said check capacitors and resistors in the line oscillator, it has to be worth trying a valve first I suppose? PCF802 to the left of the line screening can. The osc coil is behind the valve.
The later chassis used some Mullard Mustard coloured capacitors they are usually OK. The plastic moulded ones are the ones to first suspect.
Check the capacitor wired across the line osc coil, one end is connected to the anode of the triode part of the PCF802. It is located under the chassis between the tagstrip and the osc coil base to the left of the PY801 valve base.
Hope this helps.
The KB hand wired chassis is one of my favorite sets they went forever and gave very little trouble. I have a few set in my collection a couple of early ones a VC53 the same as yours and no less than three "Deep scenes" ! The later sets mainly worked on testing. no fun at all!
Regards, Rich.

Aristocratinuse · 28th Mar 2016, 8:54 pm

Lovely...
Thanks so much for your help, I will have a go with checking the values & try some substitution.

peter_sol · 29th Mar 2016, 6:50 am

Look at the winding first as advised in post 4 before components.

28th Mar 2016, 1:57 am	#1
Aristocratinuse Retired Dormant Member Join Date: Mar 2016 Location: Birmingham, West Midlands, UK. Posts: 2	KB WV70 Picture fault. Any help would be greatly appreciated. Attached Thumbnails

28th Mar 2016, 6:19 am	#2
Jonster Heptode Join Date: Apr 2008 Location: Eastbourne, East Sussex, UK. Posts: 671	Re: KB WV70 Picture fault. Looks like the line timebase is running at half speed, could be a leaky capacitor or a resistor that has gone high in value in the line oscillator stage.

28th Mar 2016, 7:46 am	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: KB WV70 Picture fault. Is the 625/405 line time base switch in tbe wrong position?

28th Mar 2016, 9:56 am	#4
slidertogrid Octode Join Date: Apr 2005 Location: Peterborough, Cambridgeshire, UK. Posts: 1,898	Re: KB WV70 Picture fault. Hi, Also check the line oscillator coil, the windings had a habit of dropping down the former. Sometimes someone would twiddle the core to get the frequency right again. This is ok unless the windings continue to sag enough to short the coil out. I have only seen this happen on the early VC series chassis but it's worth a check, if you note the core position before you move it (so as it can be returned to its original position) you could try adjusting the coil to see if it will bring the picture in to lock. Only use an insulated trim tool here though a screwdriver will break the slug. Failing that as others have said check capacitors and resistors in the line oscillator, it has to be worth trying a valve first I suppose? PCF802 to the left of the line screening can. The osc coil is behind the valve. The later chassis used some Mullard Mustard coloured capacitors they are usually OK. The plastic moulded ones are the ones to first suspect. Check the capacitor wired across the line osc coil, one end is connected to the anode of the triode part of the PCF802. It is located under the chassis between the tagstrip and the osc coil base to the left of the PY801 valve base. Hope this helps. The KB hand wired chassis is one of my favorite sets they went forever and gave very little trouble. I have a few set in my collection a couple of early ones a VC53 the same as yours and no less than three "Deep scenes" ! The later sets mainly worked on testing. no fun at all! Regards, Rich. __________________ The rotation of the earth really makes my day... Last edited by slidertogrid; 28th Mar 2016 at 10:04 am.

28th Mar 2016, 8:54 pm	#5
Aristocratinuse Retired Dormant Member Join Date: Mar 2016 Location: Birmingham, West Midlands, UK. Posts: 2	Re: KB WV70 Picture fault. Lovely... Thanks so much for your help, I will have a go with checking the values & try some substitution.

29th Mar 2016, 6:50 am	#6
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: KB WV70 Picture fault. Look at the winding first as advised in post 4 before components.