CTV 1982/1983 PYE 3157 16" KT3; Teletext

Posted by: @cathovisor

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Excellent stuff. Now it's time to dig deeper into that PSU to find out why

Indeed, at least I know the TV is OK, it is a fault in the original chopper supply module.

I have a sneaking suspicion it might be the TDA2581, the waveform out of pin3 was not good and that feeds via R460/C459/R457 through to pin8 of TDA3571 on the sync module, pin8 is the hoz osc output frequency. I must admit, I'm tempted to replace the TDA2581 first to save hours of poking around to only find it was indeed duff. If it still has the fault, then continue fault-finding.

Pleased to see you have a good picture on the set now Chris, I never had any chopper faults on any of the KT3 / 30 series apart from the 4R7 surge limiter going open on the mains input panel, But of course decades have gone by since then...

That looks really good, so the issue does seem to be the startup oscillator in the TDA2581 not locking correctly to the line oscillator output from the sync module. Are the bodge components still fitted?

Posted by: @jayceebee

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the issue does seem to be the startup oscillator in the TDA2581

That was the conclusion I came to, I will check my stock and If I have one will change it and try the original board back in the set.

Posted by: @crustytv

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I have a sneaking suspicion it might be the TDA2581, the waveform out of pin3 was not good and that feeds via R460/C459/R457 through to pin8 of TDA3571 on the sync module, pin8 is the hoz osc output frequency.

Posted by: @jayceebee

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Are the bodge components still fitted?

No they were removed

Posted by: @crustytv

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I'm convinced the previous person in here was either fooled by the loss of supply to the teletext board, which give the exact symptom of sync loss, or as you say, they tried to solve the picture shift problem, made it worse and gave up!

OK, we'll call those two spurious component's, symptom bodges, and remove them.

The set has been on all afternoon and for the most part it has behaved itself, the CRT is really waking up.

I've noticed a couple of things that need looking into. Although the Grey-scale looks pretty good, there are a few tweaks that are needed to static convergence, from a distance it's less noticeable, you certainly see it close up and on teletext. I'll need to study the manual on how this is achieved. Another, is on occasion the whole screen flashes red, only for a second before returning to normal. I've not looked at the RGB board at, so will over the coming days.

@crustytv As long as it's not the "flashing red" a certain Japanese manufacturer had in their early widescreen sets, which turned out to be the CRTs themselves...

@cathovisor If you mean CRTs that had curvature in one plane only then it wasn’t confined to their 16:9 sets. Some of the late 24 & 29” 4:3 models had a failure rate nearly as bad as the infamous Philips ESF 16:9 series.

Although they gave legendary pictures setting up a replacement CRT could seriously harm your productivity for the day.

Luckily I missed out on the Philips tube fiasco. I had left the trade by then.  We did have a few failures on the large screen Sony sets but they were of an age then that tube replacement cost would write them off.  However you could isolate the heaters from earth and identify the relevant pin on the LOPT, cut the print and run a wire from the LOPT earth pin to the CRT base which provided a cure. (Copyright Bodgett & Leggitt Inc) 😉 

I never had a HK short in a PIL tube as fitted to the KT3 though. To eliminate the RGB board it could be swapped and the set run on test. ISTR there are some PCB spark gaps on the tube base? Is there any grot in them?

Thanks to @michael-dranfield who sent me parts for my broken teletext remote, I have been able to make one good out of all the bits. The remote is now fully repaired, physically, electrically and working a treat. With the PYE Teletext now complete, this neatly brings this thread to a close.

Ah, so the remote that was in my loft for probably 35 years or more lives on as an organ donor! That's pleasing to see.

It came from a surplus electronics shop off the A40 somewhere near either Greenford or Northolt, when such shops were a 'thing'. In a way, it's a good job Field Electric aren't still in Borehamwood, a place many BBC Elstree engineers would visit in its day...

Posted by: @jayceebee

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@cathovisor If you mean CRTs that had curvature in one plane only then it wasn’t confined to their 16:9 sets. Some of the late 24 & 29” 4:3 models had a failure rate nearly as bad as the infamous Philips ESF 16:9 series.

Although they gave legendary pictures setting up a replacement CRT could seriously harm your productivity for the day.

I do indeed... I'm now wondering if the Philips tube you describe was the one used by Electronic Visuals for their 16:9 monitor. We had two of those as transmission monitors in TC5's production control galleries and the tubes failed very quickly indeed: I remember ringing up Blackburn (it was still operational then) to ask if it had even a near equivalent, to be told it hadn't. As the gallery 'stack' had been built around this monitor, it caused a problem replacing it so in the end we elected to gut the monitor and fit a Thomson domestic chassis inside it. And I still remember hacksawing the lugs of the Thomson CRT to make it fit...

Posted by: @cathovisor

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Ah, so the remote that was in my loft for probably 35 years or more lives on as an organ donor! That's pleasing to see.

In which case, many thanks also to you Mike 👍 

The internally broken (Mylar keypad interface cable split) teletext remote I found in my stores, although the correct type was badged Philips, the TV is PYE.

Included in the box of remote parts I received from Michael, was the broken outer shell, which was PYE what fortune! Thankfully, Michael also included all the broken grips. I used araldite and reinforcing strips for the repair of the case. I then used the keypad Mylar in the box with my circuit board. Put it all together this morning, it held firm and functioned perfectly. It's a mixture of three donors, yours, Michael's and mine. I now have a PYE remote for a PYE TV, thanks to you guys.

Serendipity in action.