Temperamental Pye FV1 - pulling at top

[retroaudio]

I have a Pye FV1 which has had lots of work done on it to bring it up to scratch. The CRT is excellent and focus is good. However, after 40 to 45 minutes after warm up, it develops what appears to be a problem. The top inch or so of the line structure begins to break up; then after a minute or so a second line appears.
A tweak of the contrast cures it for about a further two minutes, but eventually it starts at the bottom of the tube.

The brightness and focus are not affected, nor does the picture roll at any point. The line hold wirewound has reached the end of its track at first - I thought that might be the problem. It should be 10,000 0hms but is closer to 8,560. I am not technically skilled beyond old radios. That is why I have posted this question. Is this just a quirk of an old set given they were not meant to be on for long periods or has a fault developed? Any advice would be appreciated

Alex

[Duke_Nukem]

First off, when you mentioned problem with occurred initially at top & bottom of picture it implied to me a frame related fault. However the line hold being at one end of its travel plus line structure breaking up would suggest a line fault.

The DC for the line hold pot is shared with the frame osc, so I’d start there. If the decoupling electrolytic C77 in attached pic is leaky then this’d drag down that supply and hence the line pot would tend to be at one end. Similarly, if the series R77 resistor were high in value. I guess it is also feasible that excessive screen current in the frame output valve just might have an effect.

I was initially tempted to blame the sync genny in area of V12 (I never really trust them metal rectifiers), however not sure how a frame sync fault could effect the end of the frame scan, but anyhow it is another circuit that is common to both frame and line circuits so worth checking. I think V11 is supposed to be a limiter, hence the size of the vision signal that drives – and hence the contrast setting - shouldn’t have anything more than a very marginal, if any, effect ? Anyhow, once the chassis is out it won’t take a mo to check the resistors in that area.

But if I were a betting man I’d be heading straight for C77 – if low in value then the frame oscillator will be modulating the bias for the line osc.

Otherwise, can you post a pic of the set during the fault condition ?

TTFN,
Jon

[Danny]

Hi
I had similar problems on my VO9 and it turned out to be the main smoother, but if you haven't changed c77 then I would; thinking it's past its sell-by date.

My set started with line pulling to the top, then as things got worse, line hold was beyond the travel of the hold control.

Danny

[oldeurope]

Maybe this thread helps here:
https://www.vintage-radio.net/forum/...ead.php?t=1549
Kind regards,
Darius

[retroaudio]

Thanks to everyone for their advice.
I am aware that we don't have the same choice of high voltage caps as were available in the past. So, after taking on board the advice, I went for the nearest match I had, although I may change it later.

The original cap was an electrolytic 12uF capable of standing around 300 volts. I put in a modern 10uF at 450v working voltage using the old disconnected cap as a support to attach the physically much smaller component to the set. I tend to put components in with cable ties or a glue gun as long as the ties or glue hold the component securely and prevent any terminals moving and connecting with anything they shouldn't This seems to have solved the problem.

The set is more stable and the line hold has gained travel which means it can be adjusted if it needs tweaking when the set warms up and runs for some time.

I have been able to watch "Hobsons Choice" some episodes of "nearest and dearest" and the original Peter Cushing version of "1984" uninterrupted by adjusting the set, so things can't be bad.

Thanks Again Alex