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Old 26th Dec 2019, 2:10 am   #1
Rematzz
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Default Pye television 1956 screen problem

Hi all, I have just received a pye television model 17TCDL from 1956, it takes a long time to warm up and when it does there is only half of the screen showing up.

Am quite new to television repairs and this one has really got me stuck.

If someone could give me a bit of advice it would be very much appreciated.

Also while I remember someone told me it could mean that the crt tube has reached the end of it life, is this true?
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Old 26th Dec 2019, 12:04 pm   #2
paulsherwin
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Default Re: Pye television 1956 screen problem

It this TV completely unrestored? If so, it's likely to need a fair bit of work doing to it before it is usable. I'm surprised an unrestored 50s telly works at all.

What is your level of expertise with vintage valve technology generally? A 50s TV is a tough first project.
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Old 26th Dec 2019, 12:12 pm   #3
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Default Re: Pye television 1956 screen problem

The CRT appears to be quite good, has Paul states quite a lot of work required on the chassis.
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Old 26th Dec 2019, 12:20 pm   #4
slidertogrid
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Default Re: Pye television 1956 screen problem

Hi, Welcome to the forum! The fault you have is in the frame stage. There may be other faults once you give the set some signal.
To be honest it is fairly remarkable that you have anything on the screen at all if the set is unrestored .
Most if not all of the wax capacitors will need replacing they will be (electrically) leaky.
The capacitors being leaky are almost certainly what is causing the frame fault.
It would be best to get a circuit diagram for the set then you can identify the wax capacitors and get some suitable modern replacements.
Plenty of advice and help on the forum as you go.
The Tube looks fine the display looks bright and in focus. the signs of a worn tube are usually a dim display or the brighter parts of the picture (highlights) going 'silvery' or out of focus.
It would be helpful to know your level of experience as far as restoration is concerned.
There are some precautions to take when working on a old TV set, High vacuum CRT, EHT and live Chassis to name a few... but there is little point in bombarding you with information that you may already know.
Good luck with the set it will provide hours of fun!
Rich.
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Old 26th Dec 2019, 12:58 pm   #5
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Default Re: Pye television 1956 screen problem

Thanks for the replies so far, this is my first television project but have worked on valve radios and record players before.

I've had a lot of bad advice over the years and was put off from buying this television, but I have always wanted one and this one is a true barn find, well it was stored in a old piggery.

Some of the valves still have the supplier notes on them dating to 1957.

I haven't had any experience on valve televisions at all, so I thought I would get one to learn. I have managed to get the circuit diagram and the service sheets for it aswell.
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Old 26th Dec 2019, 5:03 pm   #6
slidertogrid
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Default Re: Pye television 1956 screen problem

The first thing to do is to check the mains plug is wired the right way around that is mains neutral to chassis. Always unplug when working on the set don't rely on the set's on - off switch.
You will need to access the capacitors under the chassis to replace them.
I usually replace a couple at a time checking as I go and testing after each replacement or two so if you do make a mistake it's easy to recheck what has been done. The choice to just replace the capacitors with modern ones or fit the modern ones inside the original cases is up to you. It depends if you want the chassis to look original or just work.
I would replace or disconnect the mains filter capacitor connected across the mains supply (If still fitted) before going much further as it may go short and blow itself apart if its an old waxie..
The two large front control knobs will have to come off to remove the chassis. I'm not sure if they pull off or need screws releasing first. Then it's a case of removing the chassis to the extent of the wiring connecting to the tube and supporting it to work on the underside. it may be that you will have to remove the tube base depending on the length of the wires.
Hopefully the set is a wired metal chassis and not the early PYE PCB chassis..?

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Old 26th Dec 2019, 5:42 pm   #7
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Default Re: Pye television 1956 screen problem

If there is at least part of a scanning raster on the screen to see (which you have) its appearance can tell you an awful lot about the fault.

For starters the raster width is about right, so this means that the HT supply to the horizontal osc and H output stage is roughly correct and the H osc frequency roughly correct and because you have reasonable CRT beam current, the EHT is working and the focus is not way off, so the CRT is probably ok or at least good enough.

You won't be able to assess the signal process circuits and audio/video system until you feed it with a known good test signal.

The main fault that is evident is severely impaired vertical linearity and loss of vertical scanning height.

Since the vertical scan starts at the top, the vertical yoke coils are supposed to have a linearly increasing current, with the peak current occurring at the bottom of the raster, prior to V flyback. This is why, when many vertical scan faults appear, there is loss of height and compression of the scanned lines toward the bottom of the raster as the drive circuit fails to supply the required peak scanning current.

So, the CRT raster you are looking at (and the beam deflection you are seeing) is in a way like an oscilloscope recording of the yoke currents.

There are multiple reasons why this could happen in an old set, I will just list a few:

1) Distorted drive waveform to the vertical output valve (waxies & resistors defective)
2) DC conditions incorrect (cathode and or screen resistor on vertical output valve faulty or faulty screen bypass if there is one)
3) Vertical output valve cathode bypass electrolytic faulty (if there is one)
4) High value resistors in linearity circuit/feedback components, leaky waxies.
5) Vertical output valve itself defective and low on emission.
6) Reduced HT to vertical output stage, of faulty electrolytics allowing the supply voltage to drop as the yoke current increases.

So in summary the vertical output valve's condition, its DC conditions and the shape of the drive waveform presented to it and the qulality of the power supply can all affect the vertical scan amplitude & linearity.

So in this sort of case, before doing anything you will get further ahead if you renew all the capacitors in the vertical oscillator and output stage (where they are waxies & any electrolytics) and check every resistor for the correct value. Then check the HT supply to the stages and replace the V output valve if that does not fix it. It is fairly easy to see with a scope too, if the vertical drive waveform is abnormal, or the problem is in the output stage itself.

Vertical output stages in valve sets are a lot like audio amplifiers in their design, though there are usually more feedback components (resistors & capacitors) around the stage to help attain good scanning linearity.

PS: if it is a hot chassis set (neutral to chassis) its best to power it by an isolating transformer and earth the chassis before connecting other earthed apparatus like a scope to it.

Also, it is obvious from the remarks above, this is the reason why some TV restorers replace all the waxies and all the electrolytics in a set, prior to powering it, as it significantly reduces the number of faults to track down and drastically improves the reliability and could be regarded as the basic initial restoration.

Last edited by Argus25; 26th Dec 2019 at 5:55 pm.
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Old 26th Dec 2019, 6:34 pm   #8
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Default Re: Pye television 1956 screen problem

To reinforce the above, it is extremely likely that all the wax capacitors between 0.001uF and 0.2uF are leaky. Not all will cause obvious faults - it will depend on their position in the circuit.
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Old 26th Dec 2019, 7:32 pm   #9
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Default Re: Pye television 1956 screen problem

Hi Remataz,
Welcome to the world of vintage telly repairs.

You have a good set to start on there.

The first thing to do is to replace (or at least for now cut one end off) the two mains input filter capacitors, C37 and C38 (on trader sheet 1379), one before and one after the mains switch. These need to be class X types.

As you are new to TV repair, then I might sugest replacing one capacitor at a time and powering the set in between to see what effect each new component has.
A circuit is essential if you want to understand what all the parts do.

Good points about your set. The line output transformer (LOPT) seems to be OK and the CRT seems to be good.
A dim raster at the moment can be due to a low A1 (G2) voltage on the CRT which is probably down to a leaky boost capacitor in the line output stage. Also we have found that CRTs that have not been used for decades can be a bit dim at first but gradually wake up as you start to use them again.
I note as well that your set has an early solid state HT rectifier and these don't seem to last too well.

Feel free to ask for advise here.

Cheers
Andy Beer
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Old 28th Dec 2019, 9:20 pm   #10
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Default Re: Pye television 1956 screen problem

All the signs are that you have a good basis for restoration, as others have said, the set will require replacement of all wax capacitors and electrolitics.
It should be quite straightforward given that you have done similar work on valve radios.

As you probably know, you will need a standards converter to use the set, these are not cheap, but a must if you want to watch a 405 line set.

I reckon your set was working fine when retired!

Mark
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Old 29th Dec 2019, 10:44 am   #11
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Default Re: Pye television 1956 screen problem

IMHO These are well engineered and designed televisions which will show off 405 line pictures at their best.

No mean level vision AGC here, with PYE's APC giving a true black level and with NFB on the sound output valve, "the pentode sound a thing of the past". A tone control to manage the high notes unfamiliar to many am radio listeners and a good loudspeaker, this set was the bees knees!

My family replaced an ageing Bush TUG26 with the Continental CW17 console model and what a difference.

There are some stock faults but the schematic is all important.

The same chassis is used in PYE CW17, CS17 CTM17T, and your 17TCDL. There is also a fringe version. I am sure that I have the Service Details in one of the Newnes Books so if you have difficulty in getting the schematic, let me know and I will scan it for you.


I also understand that the PYE CTM4 circuit (late version) is similar and there are a number of threads on that model here and on other vintage TV sites.

Chris

Last edited by simpsons; 29th Dec 2019 at 10:55 am. Reason: Info update
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Old 29th Dec 2019, 11:38 am   #12
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Default Re: Pye television 1956 screen problem

See also on this site, PYE V14C and PAM 580. The later will take you to Invicta models which have the same innards but different cabinets.
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Old 29th Dec 2019, 12:44 pm   #13
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Default Re: Pye television 1956 screen problem

Circuit diagram of the frame timebase. Replace all the marked capacitors. Don't bother to test them, they'll all be leaky.
C85 and C86 are the sawtooth forming capacitors. The cathode bias resistor of V22 is un-bypassed. C116 (180pF) feeds the flyback pulse to the line flywheel discriminator. Possible function is to prevent hooking at the top of the picture.

DFWB.
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Old 29th Dec 2019, 1:18 pm   #14
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Wink Re: Pye television 1956 screen problem

You beat me to it David.
First you need to identify which chassis is fitted in your receiver. Pye went a bit mad at this time fitting totally different chassis in the same model with the same model number!
I have looked through my PYE manuals and discovered this one for the CW17, CW17C, CS17C, CTM17 and 17TCDL.
There are three circuits. Ref RV4A RV4B and RV4C. The differences are noted on the bottom of the circuits to help identify which chassis is fitted.

As advised, replace every wax capacitor in the frame oscillator/output stage and you should obtain a linear raster. It's my guess that you will obtain quite a decent picture after carrying out these replacements. You can then work your way through the remaining caps replacing one at a time to avoid headaches.

Take plenty of pictures as it can be difficult with these wire wrapped tags in Pye receivers to locate a connection especially if you have been disturbed half way through! Avoid the blanket approach unless you feel VERY confident.

Yes these give a first class picture with a double interlace filter, a bit like a smoothing circuit in a power supply!

Avoid the over cleaning madness before you attempt the challenge..
Regards, John.
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Old 30th Dec 2019, 9:29 pm   #15
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Default Re: Pye television 1956 screen problem

Thanks everyone for all the advice so for.

I've been very busy over the last week, but yesterday I managed to take it apart and have a look at the circuit.
One of the capacitors have blown and all the others dont look to healthy, which isn't a surprise. But I was surprised that the tv cabinet it was housed in has so much woodwarm, that as I took the brackets off, the wood just crumbled.

So the cabinet has gone to a friend to see what he can do with it, and I'm going to have a better look at the circuit at the weekend.
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Old 2nd Jan 2020, 5:46 pm   #16
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Default Re: Pye television 1956 screen problem

Is that the Robin Day cabinet?
Something of a collector's item in its own right, although I personally prefer the 'Continental'.
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Old 3rd Jan 2020, 1:30 am   #17
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Default Re: Pye television 1956 screen problem

This is the set designed by Robin Day
The model is CW17s
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Old 4th Jan 2020, 1:22 am   #18
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Default Re: Pye television 1956 screen problem

As well as the waxies, don't forget to replace the screen grid bypass electrolytic c91 on the vertical output valve's screen grid, if it has gone low capacity and or high ESR it will give you pretty much exactly the fault you are seeing.
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Old 5th Jan 2020, 7:48 pm   #19
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Default Re: Pye television 1956 screen problem

If you want to work on the chassis while the cabinet is away being restored it may be worth considering making some sort of jig to support the tube so you can reconnect the chassis and support it to work on the reverse side.
Maybe something could be simply made using wood and / or Dexion shelving if you can find some old bits? These often turn up in house clearance auctions.
Take precautions with the tube though while it is out of the cabinet and not behind safety glass!
As well as the wax coated capacitors you may find some small brown Hunts branded capacitors. These are best removed by snipping the wire each end and carefully lifting them out. it is very easy to have one crumble into bits and then you have to consult the layout and parts list diagrams to identify its value. (Capacitance and working voltage)
Any chance of taking a photo of the underside of the chassis ?
If you take a methodical approach to this you will soon have it working again!

Rich
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Old 17th Jan 2020, 11:24 am   #20
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Default Re: Pye television 1956 screen problem

Hi, all just got news from my friend about the cabinet/chassis, it's no good, its completely rotten.

Will upload pictures of the circuit later, my friend is going to source me another cabinet or build me one.
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