Ekco TSC30A Picture shift problem. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 14th Mar 2014, 2:38 pm

Here's a problem that is becoming more common with our vintage TVs. Magnetised laminations of the scan coils.
I experienced something similar with a Pye BV20. In that set the picture was deflected horizontally, no matter what one could do with the shift magnets the picture remained off-set.
This time it is an Ekco TSC30 which has a picture shifted vertically and again no adjustments of the mechanical picture shift controls will move the picture down into the centre.
It is all too evident the laminations of the scan coils have become magnetised. With the Pye LV30 I was lucky,the solution was effected by discharging a capacitor across the line coils.
This time it is not proving not be so easy,tricks like discharging capacitors and applying full HT momentarily has not effected a cure.
For the time being I've introduced a DC current into the frame scan coils and doing this has moved the picture down in the centre of the mask.
The Ekco TSC30 is essentially a pre-war set and is very similar to the 1939 TSC902 which was developed from the model TS201 made a year earlier.
My set is a TSC30A which has the added refinement of sound and vision noise limiters.

DFWB.

Freya · 14th Mar 2014, 5:23 pm

Could you pass some AC through the coils (removed from circuit) I seem to remember using some fancy AC coil on the lathe at school to demagnetise the chuck.

FERNSEH · 14th Mar 2014, 6:07 pm

I did try that although it was only the 4 volts from the heater supply. Introducing a DC current though the frame colis has centred the picture but of course this should be only a temporary measure.

DFWB.

Freya · 14th Mar 2014, 6:56 pm

How magnetised are they, will they hold a needle ? or pin

I have the Ekco data if you want it.

Norman Raeburn · 14th Mar 2014, 8:48 pm

Hi David, This maybe a daft idea, could you not try a degaussing coil? Regards, Norman

Heatercathodeshort · 14th Mar 2014, 9:48 pm

Very common with the Pye B18T and LV30 David. A flash with any fully charged electrolytic 10-100uf usually solves the problem. J.

FERNSEH · 14th Mar 2014, 9:52 pm

Quote:

Originally Posted by freya2871

How magnetised are they, will they hold a needle ? or pin

I have the Ekco data if you want it.

Hi Freya,
although the frame scan coils exhibit all the characteristics of magnetised laminations they can not attract a pin.
Interesting to note that when the picture was in the shifted state the bottom of scan was slightly compressed and after the DC current was introduced the frame linearity improved, no compression. See the attached picture.
Picture shift is effected by moving the focus coil assembly, the set does not have shift magnets. Perhaps the problem is not the scan coils, I giving serious thought about the focus coils, an asymmetrical field perhaps?
Many thanks for the offer of service information. I've have a copy of the original service cards.

Hi Norman,
It might well get to that, degaussing coils.

DFWB.

Heatercathodeshort · 14th Mar 2014, 10:48 pm

What a cracking picture. You can't fail with an EKCO. J.

FERNSEH · 15th Mar 2014, 2:28 pm

Acting on a tip from Forum member BrianC I've reversed the connections to the focus coil. The results can be seen on the attached picture.
This action has confirmed that the focus coil is faulty and the only thing to do now is compensate for the faulty part.
After repositioning the scan coils the picture is deflected down from centre.
A DC current will have to be introduced in the frame coils to shift the picture upwards.

DFWB.

14th Mar 2014, 2:38 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Ekco TSC30A Picture shift problem. Here's a problem that is becoming more common with our vintage TVs. Magnetised laminations of the scan coils. I experienced something similar with a Pye BV20. In that set the picture was deflected horizontally, no matter what one could do with the shift magnets the picture remained off-set. This time it is an Ekco TSC30 which has a picture shifted vertically and again no adjustments of the mechanical picture shift controls will move the picture down into the centre. It is all too evident the laminations of the scan coils have become magnetised. With the Pye LV30 I was lucky,the solution was effected by discharging a capacitor across the line coils. This time it is not proving not be so easy,tricks like discharging capacitors and applying full HT momentarily has not effected a cure. For the time being I've introduced a DC current into the frame scan coils and doing this has moved the picture down in the centre of the mask. The Ekco TSC30 is essentially a pre-war set and is very similar to the 1939 TSC902 which was developed from the model TS201 made a year earlier. My set is a TSC30A which has the added refinement of sound and vision noise limiters. DFWB. Attached Thumbnails

14th Mar 2014, 5:23 pm	#2
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Ekco TSC30A Picture shift problem. Could you pass some AC through the coils (removed from circuit) I seem to remember using some fancy AC coil on the lathe at school to demagnetise the chuck. __________________ Stephen _________"It`s only an old telly" ___

14th Mar 2014, 6:07 pm	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco TSC30A Picture shift problem. I did try that although it was only the 4 volts from the heater supply. Introducing a DC current though the frame colis has centred the picture but of course this should be only a temporary measure. DFWB.

14th Mar 2014, 6:56 pm	#4
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Ekco TSC30A Picture shift problem. How magnetised are they, will they hold a needle ? or pin I have the Ekco data if you want it. __________________ Stephen _________"It`s only an old telly" ___

14th Mar 2014, 8:48 pm	#5
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Ekco TSC30A Picture shift problem. Hi David, This maybe a daft idea, could you not try a degaussing coil? Regards, Norman

14th Mar 2014, 9:48 pm	#6
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco TSC30A Picture shift problem. Very common with the Pye B18T and LV30 David. A flash with any fully charged electrolytic 10-100uf usually solves the problem. J.

14th Mar 2014, 10:48 pm	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ekco TSC30A Picture shift problem. What a cracking picture. You can't fail with an EKCO. J.

15th Mar 2014, 2:28 pm	#9
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco TSC30A Picture shift problem. Acting on a tip from Forum member BrianC I've reversed the connections to the focus coil. The results can be seen on the attached picture. This action has confirmed that the focus coil is faulty and the only thing to do now is compensate for the faulty part. After repositioning the scan coils the picture is deflected down from centre. A DC current will have to be introduced in the frame coils to shift the picture upwards. DFWB. Attached Thumbnails