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CTV New Workshop. First Up ITT FT110

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Jayceebee
(@jayceebee)
Noble V-Ratter Registered
Posts: 1524

Maybe I should practice what I preach 😏 . The very first thing I should have done was disconnect the tripler but I was so deflated after the success of curing the tripping I just walked away and had some lunch and then followed your successful progress. I still don't think I'm out of the woods, the tearing effect appears to be EHT related. Maybe the replacement tripler could be at fault or the CRT could be to blame. Unfortunately the set has an ITT branded CRT and internal EHT pickup problems with theirs were common.

John.

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Topic starter Posted : 02/05/2021 9:35 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered
Posts: 1524

After the B & O and the ICC5 repairs I'm beginning to get into my stride now in the new workshop and have got stuff placed now where I'm comfortable, time to turn to something a little more challenging so it's back to the FT110.

A big thanks go to Malc Scott for the generous gift of a replacement five lead tripler, it was indeed the cause of the EHT tearing on high brightness and not the CRT, thanks again Malc. An assessment of where the set stands at the moment reveals multiple issues. Movement of the chassis again causes multiple problems, colour control doesn't work, strange colour which looks a bit like missing R-Y, terrible blue convergence with an unadjustable droop at the LHS and an intermittent lack of height problem and the CRT base connector is problematic.

A lot of the chassis movement issues such as tuning drift and poor definition responded to resoldering of the chassis frame but even just that wasn't without it's problems. On several points the new solder would not take and I had to resort to removing it all and brightening up the metal lugs. It was quite difficult to get what I thought was a good looking joint trying to solder with the chassis vertical and ended up doing it with the set face down.

Next I tackled the blue convergence, the R/G at the left and right edges isn't great but the blue was just terrible. Removing the board from it’s plastic holder showed some previous repair work, R655 had been replaced sometime ago but instead of a 68Ω for some reason a 560Ω had been fitted and was badly cooked. The correct value improve things dramatically.

Attention now turned to the odd chroma, now it’s a very long time since I tackled a totally discrete PAL decoder so on went the thinking cap, the fact there was some locked colour at all ruled out the reference osc so where to start?. The picture sort of reminded me about the early RBM decoder in which the bistable would drop into the wrong phase after a channel change so that’s where I stuck the scope but the 7.8KHz squarewave was text book. I’m pleased I followed my hunch as I got lucky when I looked further, there was just a mangled signal at C866 feeding bistable output into the R-Y demod. A nice new 10nF brought back some red but the colour wasn’t right, setting up R828 and L803 around the delay line improved things no end. The no colour control was easy, just a pinged lead on the control panel.

She’s coming on but still plenty to do, R/G convergence and the intermittent lack of height, the latter I thought would be easy but it’s leading me a bit of a merry dance. The CRT is unfortunately a bit on the soft side and the CRT socket is also a bit touchy. More to follow but Carole is looking much better now.

chroma
itt1
itt2

John.

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Topic starter Posted : 25/07/2021 9:14 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered
Posts: 1524

Well the lack of height has been eventually sorted and the cause was rather unusual. The output to the scan coils was about 10V down in amplitude and various checks revealed no component problems, the fact that it was perfectly linear suggested this wasn't an issue with any of the silicon and proved to be the case.

Tests in the height control area also failed to show any failed resistors and the two blue Philips 10uF electrolytics C427/8 were half heartedly replaced to no avail. R418 and R421 were also checked and found blameless so what was going on? For no good reason I decided to measure the A1 voltage at the junction of R542/3 which also feeds R421. To my astonishment the height increased by a couple of inches top and bottom, the penny dropped immediately and sure enough on removing C521 instead of 2200pF it read only a few pF. A new cap produced a full raster and also an increase in brightness.

height

John.

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Topic starter Posted : 27/07/2021 11:59 pm
malcscott, Nuvistor, Red_to_Black and 2 people liked
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