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Old 11th Feb 2020, 9:10 pm   #1
davidbi
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Default Ekco TC138 TV ( driving me nuts )

Can anyone help with a problem on an Ekco TC138. I have been renovating this set at Snellings Audio and Visual Museum /www.snellingsmuseum.co.uk
The whole picture has started to creep up vertically from bottom to top by about half an inch. I had enough of a problem just filling the screen and just when I thought it was nearly perfect it started to rise leaving a gap at the bottom and missing the top if picture. The scan remains linear. Any suggestions would be helpful. Also I can get sound and no picture or picture and no sound just an off tune hum! Please note last2 images are mirror image!
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Old 11th Feb 2020, 9:57 pm   #2
high_vacuum_house
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Default Re: Ekco TC138 TV ( driving me nuts )

Good evening,
Are there some shuffle plates around the neck of the CRT. Probably mounted on the rear end of the scanning coil assembly. My Ekco TMB272 has one and pushing it up and down makes the picture shift left and right and pushing it sideways shifts the picture up and down. If not it could be a leaky capacitor in the frame stage causing a DC offset on the scan coils.

Christopher Capener
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Old 11th Feb 2020, 10:34 pm   #3
FERNSEH
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Default Re: Ekco TC138 TV ( driving me nuts )

The Ekco TC138 is a development of the model TS88 so I assume the frame timebase circuit is the same.
Because the cathode current of the output valve flows through the scanning coils there will be a degree of picture shift. Excess current through the SP61 will a result of leaks in C20 or C21.

DFWB.
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Old 12th Feb 2020, 1:20 am   #4
davidbi
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Default Re: Ekco TC138 TV ( driving me nuts )

No shuffle plates Chris unfortunatley, but I will check the SP61 again, I think I have changed the caps in framestage but I will recheck
Thanks
David
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Old 12th Feb 2020, 11:02 am   #5
Heatercathodeshort
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Default Re: Ekco TC138 TV ( driving me nuts )

Check the caps again. I have a number of variants of these receivers and have never experienced frame creep providing the frame caps have been replaced. The SP61 is not an ideal FOP valve but appears to work well with the TS88 series. It is very easy to miss one. The best method is to locate each one on the circuit and mark it with a highlighter as you replace them. This way you find them all.
Check also the screened cable to the top cap of the SP61 for leaks. It was a stock fault in its day. Very reliable receivers. An interesting one! John.
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Old 12th Feb 2020, 11:08 am   #6
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Default Re: Ekco TC138 TV ( driving me nuts )

Cheers for that I will check next Tuesday and report back.
David
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Old 12th Feb 2020, 11:35 am   #7
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Default Re: Ekco TC138 TV ( driving me nuts )

I took these pictures a few moments ago.
As you can see you should not be struggling for height with any Ekco model. I turned the height control almost fully to take this picture and amazingly the linearity is not at all bad!
This TS88 has not been turned on for around 3 years and it came straight on with no adjustment. It needs a little twiddle but demonstrates Ekco quality 70 years ago. [As David has mentioned the original TS88 chassis was employed with slight variations in many Ekco models.] The later versions such as the TC138 being superhets. The rest of the circuit remained the same. Regards, John.
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Old 12th Feb 2020, 6:40 pm   #8
davidbi
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Default Re: Ekco TC138 TV ( driving me nuts )

Hi John
Maybe I am being a little too critical with our set. I see that the top of your picture is missing so as to get the bottom just right. I have been trying to centre the whole picture just a bit more, I can get ours to look exactley as your is so maybe I will settle for that if I can cure the scan from rising after a while. I hope this makes sense to you !!!
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Old 13th Feb 2020, 1:25 pm   #9
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Default Re: Ekco TC138 TV ( driving me nuts )

This is purely adjustment. My example would center up correctly if I pulled it from it's sleeping place and did a bit of twiddling. It should be perfectly linear and central on the screen of course. The TS88 is more than capable of producing this.
Yours looks fine and providing it is stable, I would leave it at that.
This chassis tends to suffer from slight line drift when warm. If the SP61 is OK I would suggest you replace the two silver mica 100pf capacitors in the line oscillator. They are a common cause of drift and a stopped oscillator. Very unusual for this type of cap to play up but they do in the TS88! They tend to drastically reduce in value. John.
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Old 13th Feb 2020, 1:58 pm   #10
davidbi
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Default Re: Ekco TC138 TV ( driving me nuts )

Yes I have got a bit of a line sync problem when it first comes on, 1 minute and it remains fine. I did find a 2pf video coupling capacitor ( cannot remember C number ) this cured a poor video fault. I have never (as far as I can remember) ever had a very low pf cap have such a drastic effect on a picture and it's a lot of years now.

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