Pye 4311 export TV - service manual wanted

[GLENZ32]

Hi, I don't know how I missed this thread, but your Pye does indeed look very similar to mine, just without the fancy cabinet. Nice to see another export Pye/Ecko still in circulation and not six feet under!
P.S. Haven't forgotten about those photos of my chassis/tuner up close for you. Am planning to have a sort out/move around in the man cave shortly which will mean I can access the Pye more easily.
Cheers Glen

[dazzlevision]

Hello Glen,

Glad to have you on board now!

Yes, my 4311 is very similar to yours, apart from the fancy cabinet. However, there are many small differences in the detail of the circuitry, which I am trying to establish for my 4311, in the absence of the correct circuit - for now, anyway!

I look forward to some close-up pictures in due course.

Many thanks,

Dazzlevision

P.S. I hope your set's LOPT isn't a dud, like mine has proved to be! I was rather disappointed, as Ekco LOPTs of that era (for the UK equivalent chassis) seemed to survive well after years of inactivity.

[dazzlevision]

Hello,

Here are a couple of pictures showing progress to date.

I have fitted the UK version four push button Plessey VHF tuner, but need to make up some mounting brackets. I have also replaced quite a few passive components, trying to use "old but good" types wherever stocks allow (mainly Mullard C296 "mustard" axial Polyester capacitors). You will notice some modern "canary yellow" caps in there as well! I've also taken the opportunity to clean the PCBs and wiring as I replace components.

Removing the wax coating from the LOPT's EHT winding hasn't affected the LOPT overheating issue, so my next step is to remove the EHT winding and run the set without it. This should prove the primary is OK, in which case I will try to fit a similar EHT winding from a good LOPT of a different type, but which produces an EHT of around 15-16kV.

I also have to decide whether to leave the set aligned for UK system I or revert to CCIR, with 5.5MHz intercarrier sound. I would then have to generate CCIR RF signals to run it, but I could covert one of my Philips PM5519 pattern generators to CCIR standard and simply use it as a VHF or UHF modulator, as it will accept external video and audio inputs.

I expect that, whoever originally tweaked the IF coils to allow the set to work in the UK would only have attended to the 5.5MHz sound IF and detector stages. They probably didn't readjust the intercarrier beat trap coil in the video amplifier or the co-sound / adjacent sound attenuator traps.

I will have to use a signal generator to determine what frequency the two traps in the vision IF stages are currently tuned to, and adjust if required, but I think I had better get the LOPT situation sorted out first!

Regards,

Dazzlevision

[wd40addict]

Hi, Dazzle

what are your 'classic progressive overheating symptoms'? Have you measured the resistance of the EHT winding in cold and hot conditions to calculate the winding temperature rise?

Regards,

Paul

[dazzlevision]

Hello Paul,

The symptoms are (assuming switch-on from cold):-

Initially normal picture size and correct boost HT voltage.

After a few minutes, the Boost HT voltage starts to reduce and by the time it has dropped 30-50 volts, the primary winding is uncomfortably hot to the touch, as is the EHT overwind.

The wax coating of both windings has softened.

The width gradually reduces with reducing Boost HT line voltage.


I haven't measured the hot and cold resistance of the EHT winding. All other components in the line output stage are OK ("usual suspect" paper dielectric capacitors replaced) and line drive is correct throughout.

Regards,

Dazzlevision

[wd40addict]

Hi Dazzle,

Thanks for the clarification. My TV22 slowly starts to lose EHT volts. From cold the picture is excellent, but by about an hour it looks a bit 'muddy'. When I've measured EHT has fallen by about 500v. Boost is still OK. My primary has been rewound so suspicions are firmly on the overwind. Comparing hot and cold resistances shows a temperature rise of about 20deg which seems quite reasonable. I have not tried removing pitch etc, but enough of it has fallen off to allow some 'ventilation'.

Yours definitely sounds much more drastic. Keep us posted.

Regards,

Paul

[GLENZ32]

Eek! I hope the LOPT in mine is OK! Guess I'll find out when I get around to firing it up. There are some waxies I'll be changing first though before doing this.
Cheers Glen

[dazzlevision]

Hello Glen,

In a post I made in your Pye export TV thread, I did say that Ekco LOPTs of that era were usually OK. My Ekco T407F (a UK market set), made around the same time, is fine and has a very similar LOPT construction (albeit 405/625). Ah well..........

Regards,

Dazzlevision

[dazzlevision]

Originally Posted by dazzlevision

Hello,

Removing the wax coating from the LOPT's EHT winding hasn't affected the LOPT overheating issue, so my next step is to remove the EHT winding and run the set without it. This should prove the primary is OK, in which case I will try to fit a similar EHT winding from a good LOPT of a different type, but which produces an EHT of around 15-16kV.

Regards,

Dazzlevision

Well, I removed the EHT winding and the set ran for an hour without excessive heating (although the Boost HT was well down - not surprising with the overwind's inductance and capacitance missing). Fingers crossed, the primary winding is probably OK.

I then fitted a known good overwind from a Rank Bush Murphy A774 UHF/625 single standard hybrid mono TV chassis. This produced a much lower boost HT and narrow picture. The set ran for an hour with no significant Boost HT drop or overheating.

I noticed that the Ekco overwind has a 1cm band of Copper foil on the inside of the overwind's former/bobbin, with a split, so it doesn't form a short circuit turn. The foil is connected to the transformer's ferrite core by a short length of bare and stranded wire (and held in place by the mounting/core clamps). I am guessing this is to add capacitance between the overwinding and chassis...? In any event, I tried the effect of connecting variouspF "pulse" caps between the overwinds input wire and chassis and this did affect the picture width and boost HT, but so as to give normal scan and EHT.

I then removed the Rank A774 o/wind and fitted a NOS one from a Bush TV105 LOPT (pitch type!). This produced near normal width and boost HT but, as with a lot of pitch Bush LOPTs, it didn't last! The boost volatge started to fall and I could hear hissing from the LOPT. Looking at the Bush overwind, I could see a hot spot, where molten pitch was bubbling out! I switch ed off at this point.

Notwithstanding the Bush pitch overwind "meltdown", I think it was about right, so I shall try an overwind that is not pitch, such as the Plessey version of the Bush TV125 LOPT, which uses epoxy resin (or similar) for encapsulation, and is much more reliable.

I'll let you know how I get on.

Regards,

Dazzlevision

[Tazman1966]

Keep plugging away

[Billy T]

Originally Posted by dazzlevision

In any event, I tried the effect of connecting various pF "pulse" caps between the overwinds input wire and chassis and this did affect the picture width and boost HT, but so as to give normal scan and EHT.

Changing the value of the flyback tuning cap alters the flyback time.

Less capacitance = higher EHT, lower width, and more voltage stress on the overwind.

More capacitance = slower flyback, less EHT, more width and less strain on the overwind.

If you wish to protect and prolong the life of an 'unobtainium' lopt, increasing the value of the flyback cap then reducing the width (and consequently the boost voltage) will do the trick nicely. If optimum width cannot be obtained at a boost voltage you can live with, then the width can be increased by a reduction in the value of the S correction capacitor, found in series with the line scan coils and usually close to the horizontal linearity control. It will probably produce a slight non-linearity in the centre of the screen, but it is usually unnoticeable on program material, and the trade-off in loptx life expectancy is worth it. Adjustment of the linearity control can also give a little extra width and the visual effects on program material are usually minimal. However, if you prefer to watch test patterns, you would probably be irritated by the minor compromises, but I prefer to see a set working, and on program material, and we never had a customer complaint on any modified set.

For a true unobtainium overwind failure on foreign mono sets, here in NZ we would cut off the overwind, dispense with the EHT rectifier etc, fit a tripler (input from the line output anode) and adjust the lopt tuning cap, linearity and S correction to get the required width and linearity. It was our "pensioner special" to get TVs back in their home at minimal cost, and the improvement in image quality was well worth it as well.

If you wanted to retain a 'close to original' appearance, you could always fit a fake overwind or just hacksaw a slice across the winding, insert a plastic or card spacer then restore the outer coating. Triplers are relatively easy to hide under a big chassis and you get a bonus of better EHT stability as well.

You do have to take care with the connection to the line output anode if you do a hidden tripler installation but modern EHT cable is very reliable.

Cheers

Billy

[dazzlevision]

Hello,

Thanks to the generosity of a Forum member, I now have the full Pye service manual for this set.

I now know that I will need to attach an IF can to the VHF (CCIR) pushbutton tuner which attenuates the sound carrier at 33.4MHz. This is very close to the 33.5MHz sound attenuator tuned circuit fitted to System I (British 625 or 405/625) receivers.

I'm hopeful that a 33.5MHz IF can from a Pye11 / Ekco T418 series all-valve dual standard chassis will do nicely, as I have some in my loft - somewhere!

The only IF traps on the main IF/video/Sound PCB are two for the adjacent channel sound carrier at 40.4MHz.

The correct circuit also confirms that the first two common IF amp stages are EF85 valves and the value of the damping resistors across the IFTs in these stages.

Regards,

Dazzlevision