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Old 17th Oct 2020, 11:01 pm   #131
AdrianH
Heptode
 
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 501
Default Re: My first foray into Old model TV repairs. Ferguson 991T.

Well I had another look at the TV, checking resistors as suggested first, I did find a 1K that was actually out f the 20% at 1K3 so changed that, all others found to be reasonable, I had changed several over the general repair process.

I also hooked up the TV to the test set and had a tune. AGC disabled and signals keep low to make sure not to go into limiting. Looking at the video circuit it was easy to notch out the sound carrier at 19.5 MHz and adjacent sound carrier at 14.5 MHz they were quite noticeable.

Tuning on a spot frequency of 17.75MHz as suggested in the manual was more difficult as some of the tuning screws have been rounded off somewhat and the indicated increases hard to notice, but with a low signal input small peaks on 17.75 were generally found. From that point I opened up the scan rate over a few MHz and did a sweep of the IF video pass band, it was not as expected, But it really made very little difference to the picture on the screen.

Here are a few screen images captured on a hand held camera.
The centre of the span is 17.75MHz in all pictures.
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The marker here is at 14.5 MHz which would be the adjacent channel sound channel, so there is a notch at this point.

Click image for larger version

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On this one the marker is at 19.5 MHz where there are several notches of the sound carrier.

Click image for larger version

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On this one the marker is at 18.4MHz which with a 16 MHz video carrier would indicate a max pass of 2.4MHz, well it does to me anyway!

Click image for larger version

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The screen view, I noticed in this pic that I have a bit of line linearity to sort out, as I normally view from the right had side of the TV when setting it up, I had not noticed this, a job for the flat blade screwdriver in the line linearity magnet some time.

Think I will leave the set for a while and get my audio amp finished so I can at least listen to some loudish music upstairs when I have the chance.

Adrian
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