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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 15th Oct 2018, 12:44 am   #21
Graham G3ZVT
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Default Re: Pye LV20 Help?

I once repaired a CRT heater (in an oscilloscope) by applying a high voltage with current limitation across the heater pins. The idea is to strike an arc at the break, and form a weld. In my case the repair didn't last very long but YMMV.
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Old 15th Oct 2018, 9:00 am   #22
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Default Re: Pye LV20 Help?

That is a shame Joe. It's very unusual to find an O/C heater in a Mullard 9" tube.
Fortunately they are still a number around usually found in rotten TV22s and similar.

Any Mullard 9" tube can be fitted with a .3amp heater such as the MW22-16, MW22-18, MW22-14, MW22-14C and if you can find one, the early MW22-7 but you will need a heater transformer for this one due to the .6amp heater. Don't worry too much about ion stains, they are all part of the history.

Mazda triodes such as the CRM92 could be employed with some extensive work but the chances of finding a good one of those is almost zero! The CRM93 tetrode as used in the Ekco TMB272 is another possibility but again difficult to find unless salvaged from a rotten TMB272.

I agree with Graham, I have welded a few heaters in the past using the pulse voltage from the anode of the line output valve but the LV20 lop stage only produces a very low pulse that would not be sufficient to weld the heater satisfactorily. If you manage to bridge the break it only lasts a couple of hours unless you are VERY lucky.

Hope you can find a tube. I will keep an eye out.. John.
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Old 24th Oct 2018, 5:04 pm   #23
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Default Re: Pye LV20 Help?

He he he,
Having got a scrap quite rough LV20 from an Essex tat shop I have swapped out the CRT and scan coils (couldn't get the original ones off) and I have first light!!!

Very happy but any clues as to where to go from here would be greatly appreciated.

Joe
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Old 24th Oct 2018, 5:28 pm   #24
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Default Re: Pye LV20 Help?

Start changing a capacitor at a time in the area of the main choke, trader sheet capacitor references c54 c55 c58 c59. observe the changes as you go.
Get the timebases running first.
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Old 24th Oct 2018, 6:07 pm   #25
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Default Re: Pye LV20 Help?

That is a weird display. Tube looks 100%. Great news. J.
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Old 29th Oct 2018, 5:24 pm   #26
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Default Re: Pye LV20 Help?

Thank you for suggestions, I've changed the capacitors recommended and now have the display pictured. It seems to be rolling up and none of the controls will stabilise it, only slow it down or speed it up.
Any more suggestions greatly appreciated
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Old 29th Oct 2018, 7:36 pm   #27
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Default Re: Pye LV20 Help?

The "fuzzy" effect is due to the line frequency being off so adjust the line hold to hopefully bring that into a lock, the high pitched whistle will change and you get used to the tone eventually and be able to set it without even looking at the screen.

If its rolling then you need to look at more capacitors in the frame section,
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Old 29th Oct 2018, 7:38 pm   #28
itainthard
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Default Re: Pye LV20 Help?

Hello Stephen,

If you could that would be great.
Thank you
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Old 29th Oct 2018, 7:42 pm   #29
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Default Re: Pye LV20 Help?

Its looking good so far, any sound ?

C28-C33, I would do C56 and C57 at this stage.(trader sheet references)

Make sure your vision sensitivity and vision noise controls are set to the top of their travel.(up)
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Old 29th Oct 2018, 7:54 pm   #30
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Default Re: Pye LV20 Help?

you will also need to check that non of the preset pots on the back are open circuit
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Old 29th Oct 2018, 8:21 pm   #31
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Default Re: Pye LV20 Help?

Like I said weeks ago, just change every waxie in there and be done. They'll all be leaky.
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Old 29th Oct 2018, 8:35 pm   #32
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Default Re: Pye LV20 Help?

That's all very well if your experienced with dealing with vintage components but as the poster only has a few posts lets assume at this stage as he is asking for advice, its best to go with the training wheels to avoid a thread with 150 posts?
No offence if this is not the case Joe.
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Old 30th Oct 2018, 9:29 am   #33
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Default Re: Pye LV20 Help?

Not really understanding your point. This thread is 32 posts and most of those are about the crt. The goal is to get the set working whilst simultaneously avoiding damaging anything along the route. People will provide tips on how to achieve that, and that's what I'm doing. I think you're trying to say that changing components to cure faults on a piecemeal basis would be educational. To an extent I get that, but I'd still recommend changing waxies en masse for the huge leap forwards in the restoration process that doing that achieves. Then, you know that any further faults are not caused by waxies, and that is part of the time served, proven, engineers way of working in a process of elimination, eliminating the more obvious faults as you work your way through the repair/restoration.
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Old 30th Oct 2018, 9:41 am   #34
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Default Re: Pye LV20 Help?

Probably crossed wires, i was meaning not to change them all in one go as it leads to errors.
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Old 30th Oct 2018, 10:12 am   #35
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Default Re: Pye LV20 Help?

My own personal approach, as Stevehertz, suggests, is to change all the components likely to be faulty before I even power up a set. I do this by carefully working through the circuit diagram to ensure I don't make any errors.

The big problem is that just changing components without reference to the circuit, can easily lead to things being wired to the wrong tags! 'Well that's where it came from', without understanding whether it's the correct place or not!

We've seen threads before with 150 posts due to strange errors that have been introduced by mass component changing! I think that was Stephen's point.

So (with no disrespect to Joe), it depends on your level of experience as to whether you can manage to change all the faulty caps in one go without wiring errors and can diagnose any faults that might result.

It can be a very long road indeed getting a TV to the point of working to the best it did when it was made- the technology was marginal at the time and it hasn't got any better 60 to 70 years down the line!

All the best
Nick
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Old 30th Oct 2018, 10:18 am   #36
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Default Re: Pye LV20 Help?

The idea of replacing a few capacitors then retesting is sound but it's probably best for the person doing the work to judge the order as it will depend on the physical layout. A methodical approach would be to work by functional areas:
Power supply including heater chain capacitors (these can cause damage)
Line oscillator, sync and output (also likely to cause damage)
Frame oscillator, sync and output
and so on...

Work out which capacitors you are replacing next in the functional area you are working on and locate them on the circuit diagram. Mark them up as you go as it is easy to miss some. Power up and if it's worse then investigate, otherwise move on to the next few capacitors. After replacing all capacitors in a functional area it should work properly, otherwise investigate.

Last edited by PJL; 30th Oct 2018 at 10:32 am.
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Old 30th Oct 2018, 10:41 am   #37
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Default Re: Pye LV20 Help?

If the OP is competent and fully versed with trouble shooting without any help then replace the capacitors en mass, if not then fault find and replace the capacitors on a fault by fault basis, more is learned that way, if there are wax capacitors (or other notorious types) still in situ once the set's up and running reasonably well then replace them one or two at a time, checking the set's performance after each change.

Lawrence.
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Old 30th Oct 2018, 11:53 am   #38
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Default Re: Pye LV20 Help?

Even competent people can, and do, make mistakes - many threads on here bear witness to this so I would urge caution - all the advice given has merit

Rgds to all

John
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Old 30th Oct 2018, 12:07 pm   #39
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Default Re: Pye LV20 Help?

Yes but a competent person that has made a mistake with mass capacitor change and has to come on here asking for troubleshooting help isn't very competent.

Lawrence.
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Old 30th Oct 2018, 3:48 pm   #40
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Default Re: Pye LV20 Help?

Hi Joe,
That looks very promising.
Clearly it is trying to show a picture.
Adjusting the line hold control should make the horizontal lines appear to rotate together to from a picture.
If you get to a point where you see several pictures side by side then the line frequency is wrong. If however the picture won't stabilise in either direction then there might be a problem with the sync separator stage V7 and pulse shaper V8.
If the frame hold really has no effect then yes, as others have suggested the hold control (R39 on trader sheet, 5K) could be open circuit. The presets on these sets can be unreliable, so your spare chassis may come in useful there.

Changing one capacitor at a time is an ideal way to learn, but I do accept that with a construction style of the PYE sets it can be easier to change a few components that share solder tags at the same time.
What I would recommend is taking lots of photos before changing components in a particular area, so that if you do make a mistake it is easy to see where things were connected originally.

Cheers
Andy
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