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Old 23rd Sep 2020, 7:14 pm   #1
AdrianH
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Default My first foray into Old model TV repairs. Ferguson 991T.

I collected my cheap TV today, a Ferguson 991T.

The cabinet has seen better days, the plywood is separating it's layers so a suggestion of dampness. The corner blocks are also loose, so possibly dropped? It may be easier for me to save the front of the box and remake the top, sides and bottom from new ply, then stain and varnish to get what ever finish I can.

The back and bottom fibreboards are there, but the back is warped, so wondering what to do with it, possibly soak it and then leave it pressed between metal sheets to dry?

The TV cost 20 so I am not expecting a lot from it there are several issues that I can see.
Some are minor, but I think I have a very major issue as well.

Minor issues

1) The Ballast resistor R108, R109, R110 R111 and R112 is like a Christmas tree with other wire-wounds hanging from the terminals as sections have gone. So could do with a replacement, will look at options.

2) A PY82 has gone to air suspect a knock, not an issue I have 3 pulls to try.

3) Missing the line output and efficiency diode EL81 and PY81, but only a few to pick up, but why missing?

4) Plenty of wax and Hunts capacitors that will most likely need replacing.

The major, is I think the CRT has gone to air!
I have not confirmed this yet, but there appears to be a crack on the neck of the CRT that is 1/4 the way round. I plan to confirm this tomorrow the only way I can think of, by putting 6.3 Volts on the heater, if it smokes and burns out, it is to air. if it glows the glass is still intact.

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Old 23rd Sep 2020, 7:23 pm   #2
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Default Re: My first foray into Old model TV repairs.

It could be worse. The socket mounted on the angled bracket is for the Ferguson type 'A' Band 3 tuner. The small metal rectifier bolted to the left chassis member provides bias for the video output valve. The ion trap appears to be missing from the base of the tube neck. It is a late production model. If the tube has gone to air the heater will not glow but the neck will get warm. These present a lot of just about doable work. It looks original enough.
Try to get something singing with the minimal amount of work. The droppers may look a mess but will work ok. It is a PL81 by the way not an EL81, just a typo I guess. J.
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Old 23rd Sep 2020, 7:24 pm   #3
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Default Re: My first foray into Old model TV repairs.

Here is a picture of the crack on the neck, I can feel this in both directions with my fingernail.

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It is possible it is just a score on the tube, but I will look at options to either replace or get another TV if it is the worst case.

There are no outward signs, I would have expected to see such as missing coating on the front, or any getter coating going white, but I suspect that would be under the yoke?

I think I need to apply 6.3 Volts.

Adrian
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Old 23rd Sep 2020, 7:26 pm   #4
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Default Re: My first foray into Old model TV repairs.

Valves missing from the line output often indicate that someone has been there before and found the line transformer has gone.

Yes, powering the tube heater from a correct voltage supply from a separate power supply and looking for the 'glow' will confirm the state of vacuum.

You'll not find a replacement dropper, so test and if necessary tidy up what's there.

You'll need to get first light BEFORE going to a lot of trouble with this set, as transformer and tube problems will make it not worth bothering with - sometimes you just have to be realistic with these things.
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Old 23rd Sep 2020, 7:27 pm   #5
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Smile Re: My first foray into Old model TV repairs.

Good evening,
Could you do a couple of close up pictures of the tube neck to see if it is a crack. Is the getter in the base end of the CRT silver/black colouring or has it gone white. If it is white then is likely to have unfortunately gone to air. This would need to be addressed first as finding a working spare will be very difficult.

Unfortunately most setmakers made cabinets with a smaller depth than the length of the CRT with the consequence that quite a few 405 line CRT' television sets have had the neck damaged when the cardboard hat covering the CRT socket at the rear gets knocked or the set has been pushed over backwards and therefore due to the scarcity or spare CRT's the set is usually written off.

Christopher Capener
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Old 23rd Sep 2020, 7:28 pm   #6
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Default Re: My first foray into Old model TV repairs.

@Heatercathodeshort

Yes you are correct it is a PY81, my error. I am also trying to figure if a SCH A, SCH B or SCH C I can not figure where these markings should be.

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Old 23rd Sep 2020, 7:33 pm   #7
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Default Re: My first foray into Old model TV repairs.

Quote:
Originally Posted by AdrianH View Post
Here is a picture of the crack on the neck, I can feel this in both directions with my fingernail.

Attachment 216294

It is possible it is just a score on the tube, but I will look at options to either replace or get another TV if it is the worst case.

There are no outward signs, I would have expected to see such as missing coating on the front, or any getter coating going white, but I suspect that would be under the yoke?

I think I need to apply 6.3 Volts.

Adrian

I think that is defiantly a scratch. If it was a crack I would expect that the crack would encircle the neck altogether.

P.S don't worry about the apparent misalignment of the electron gun in the CRT. This is part of the ion trap arrangement. There should be a small magnet on a band around the neck somewhere. You would need this and it's correct orientation to get light on the screen. It looks missing to me.


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Old 23rd Sep 2020, 8:00 pm   #8
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Default Re: My first foray into Old model TV repairs.

Responses are coming thick and fast.

OK just been out in the garage with the power supply and I am smiling for now.

The heater does glow as I would expect, no signs of smoke etc, so perhaps it is just a scratch, but something I need to protect some how.

The mark in more detail
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Glow
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The small magnet is with the set, but not on the neck it is loose hanging down in the first image.

I wonder if anyone has a service manual for the set, possibly something with resistance readings for the LOPT, I could always try to measure it in situ.

Christopher perhaps I should have taken you up on the Pye VT4 when I picked up the Solartron scope?

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Old 23rd Sep 2020, 8:29 pm   #9
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Default Re: My first foray into Old model TV repairs.

I'm with Chris on this one, does look like a scratch, maybe done by twisting the trap magnet before its removal (though not sure how)?

Once a set is retired, it does become a parts doner so the odd valve may be taken. Just cos the Lop stage bottles have been half inched doesn't necessarily imply a duff lopt.

It may be worth running current through the LOPT primary for a few days to help drive out moisture and give it a fighting chance.

If heater glows correctly and you can get arc from the EHT connector then I think there is every chance for this to be a worthwhile project, the chassis looks clean. Peoples opinions vary, but I would change the coupling cap to the LOP bottle's grid and also the boost cap, give the best chance of some EHT - you can just tack them in temprarilly and return to stock if the worst happens.

TTFN,
Jon
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Old 23rd Sep 2020, 8:37 pm   #10
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Default Re: My first foray into Old model TV repairs.

As someone who has never worked up the courage to try a TV restoration I will follow this thread with interest. My late uncle worked at the Blackburn Mullard Factory for many years. He was always very proud of Mullard products.
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Old 23rd Sep 2020, 9:09 pm   #11
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Default Re: My first foray into Old model TV repairs.

There should be a strip of felt or a plastic sleeve around the ion trap magnet to prevent scratching the glass of the CRT neck when its adjusted or removed. If its missing you'll have to fabricate something. Missing valves probably mean they've just been 'robbed' for another set at some time....common when a set was written off or perhaps the set was just pensioned off because the owners bought a new set. Such sets just became 'parts donors'.

You need to position the ion trap correctly, there should be an arrow on it which should point to the front of the set when on the neck. A good starting point is about half an inch from the Bakelite base with the magnet aligned with pin 11 or 13 of the CRT base. You then rotate the ion trap gently in either direction and also forward or backwards....the idea being to obtain maximum brightness on the screen. If it is incorrectly adjusted, it can cause 'ion burn' which shows up as a darker patch in the centre of the screen.

As HCS said in post #2, you need to do minimal work initially just to get the set in a position to apply mains and hopefully something on the screen. Basically you need to establish if the line stage and CRT are viable first...'First Light' even if it's a frame collapse or even a faint raster is important. No point in spending loads of time changing caps first if the LOPT or CRT are U/S.
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Old 23rd Sep 2020, 9:11 pm   #12
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Default Re: My first foray into Old model TV repairs.

Hi Adrian,
I was impressed with how clean and rust free the chassis looks in the first pictures. That's good news about the tube- it's always a heart stopping moment when you see what looks like a crack in the glass!

Over the years, I've come to expect problems with the LOPT. I just now accept that as part of life with old TV's. Sooner or later I'm going to have to strip the thing down and attempt (usually successfully) to repair it.

The LOPT generates the high voltage for the CRT final anode from an 'overwind'. This consists of many turns of fine wire and usually generates 15-17 KV which is then rectified by the EHT rectifier valve.

With that sort of voltage on the windings, insulation breakdown is a common problem. This can be between the overwind and the core (which is grounded) or between the primary and the core or between the different windings. All the black crud and Nicotine that collects on the transformer tends to be conductive which makes the problem worse!

Over the years, the wax or pitch impregnation fails and moisture gets deep into the windings. This can cause failure once the transformer starts operating again.

There is very little to be gained by taking resistance measurements from the LOPT- it's fairly unlikely (but not impossible) for windings to fail open circuit. You won't detect shorted turns from resistance readings.

If you have a 'scope, you can do a 'ring test' on the LOPT which will tell you if it will function or is already faulty. It won't, of course, tell you if the insulation is going to fail when you power it up! You can also pass a controlled current through the windings to gently heat them from within to drive out any moisture over several days.

It would be interesting to see pictures of the LOPT inside the screening can to see what sort of construction it uses.

Good luck with what will prove to be an interesting project!

All the best
Nick
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Old 23rd Sep 2020, 10:20 pm   #13
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Default Re: My first foray into Old model TV repairs.

Quote:
Originally Posted by PaulR View Post
As someone who has never worked up the courage to try a TV restoration I will follow this thread with interest. My late uncle worked at the Blackburn Mullard Factory for many years. He was always very proud of Mullard products.
I know a ham living in Darwen that used to work there, I do wonder about the quality of things in the UK's past, especially after some of the cars we produced. Mullard does seem to have a good name. I doubt if many of these valves were from Blackburn many of them say made in Holland.
On the TV restoration, I initially said I would not do TV's, or really renovate anything, the interest was in learning more about Valve Tech and building the odd thing for myself. if successful with this one I am hoping that will be it!

Quote:
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There should be a strip of felt or a plastic sleeve around the ion trap magnet to prevent scratching the glass of the CRT neck when its adjusted or removed. If its missing you'll have to fabricate something. Missing valves probably mean they've just been 'robbed' for another set at some time....common when a set was written off or perhaps the set was just pensioned off because the owners bought a new set. Such sets just became 'parts donors'.

..snipped...

As HCS said in post #2, you need to do minimal work initially just to get the set in a position to apply mains and hopefully something on the screen. Basically you need to establish if the line stage and CRT are viable first...'First Light' even if it's a frame collapse or even a faint raster is important. No point in spending loads of time changing caps first if the LOPT or CRT are U/S.
Thanks for the pointers, I will find something to protect the tube neck from the magnet ring, even if just few layers of paper. Yes I will try and et something on the screen before going to far down the line.

Quote:
Originally Posted by 1100 man View Post
Hi Adrian,
I was impressed with how clean and rust free the chassis looks in the first pictures. That's good news about the tube- it's always a heart stopping moment when you see what looks like a crack in the glass!

.....snipped.....

It would be interesting to see pictures of the LOPT inside the screening can to see what sort of construction it uses.

Good luck with what will prove to be an interesting project!

All the best
Nick
I will take a picture of the LOPT tomorrow, I am saving as many images as I can on my PC. When I bring the set indoors I will apply a few mA through the LOPT, where would you suggest to feed it? I am thinking from the 'Width' setting point C to F the cap of V12 (Sheet 1095) Also thinking of just around 5 mA, I see the PL81 will do around 45mA, but guessing that is being pulsed and not constant all the time.

As to the state of the chassis, it has had a wipe over before the pictures, there is a spot of rust under the CRT on the chassis 4th picture first post.

I plan to go over the chassis tomorrow using a cloth on a stick, with a bit of acetone soaked in, just to help clear some more of the crud.

Last comment for tonight I have found a SCH D on the card just above the frame linearity control, so should have all factory modifications done to it.

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Old 23rd Sep 2020, 11:26 pm   #14
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Default Re: My first foray into Old model TV repairs.

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I will apply a few mA through the LOPT, where would you suggest to feed it? I am thinking from the 'Width' setting point C to F the cap of V12 (Sheet 1095)
Adrian
It's essential to include the EHT overwind otherwise there is little point.

So from the the anode of V13 EY51 - to one of the width taps. it's the wire ended valve perched on the LOPTX, the anode is the single wire end.

Bung about 30-40mA through it. I found a 12v wall wart connected directly across a similar transformer was in the right ball-park. the resistance was about 300 Ohms so that would put 40mA through it.
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Old 24th Sep 2020, 7:16 am   #15
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Default Re: My first foray into Old model TV repairs.

The ion trap on this model is incredibly tight due to a very strong retaining spring. You have to take care when fitting and definitely release some of that tension on the spring. If it is just a scratch it should hold up ok. John.

PS Picture of a 991T ion trap complete with it's crocodile grip spring removed from a 991T chassis recently kindly donated by another Forum member. This ion trap does not have the protective sleeves on the pole pieces, it's metal to glass contact. J.
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Old 24th Sep 2020, 7:59 am   #16
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Default Re: My first foray into Old model TV repairs.

Quote:
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I know a ham living in Darwen that used to work there, I do wonder about the quality of things in the UK's past, especially after some of the cars we produced. Mullard does seem to have a good name. I doubt if many of these valves were from Blackburn many of them say made in Holland.
Adrian
I think that my uncle was involved with the glass area of tube manufacture rather than valves. There was a Mullard factory very close to me called Mullard Magnetic Components. I assume they were involved in making magnets for ion traps etc. You could actually hear it humming at times and smell a warm "electrical" smell coming from it. I think that they were very good employers, he was certainly happy there.
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Old 24th Sep 2020, 8:38 am   #17
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Default Re: My first foray into Old model TV repairs.

First set I ever did... CRT isn't the greatest in mine, but still working
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Old 24th Sep 2020, 9:31 am   #18
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Default Re: My first foray into Old model TV repairs.

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My late uncle worked at the Blackburn Mullard Factory for many years. He was always very proud of Mullard products.
In case you have not seen it, there is a great film about the Blackburn factory, available here: https://www.youtube.com/watch?v=GDvF89Bh27Y.
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Old 24th Sep 2020, 9:34 am   #19
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Default Re: My first foray into Old model TV repairs.

Search Youtube for Mullard Blackburn and I think there will be around 4 films to be found, I have two saved to disk.

Thanks for the comments, bit of a late start today must have been tired.

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Old 24th Sep 2020, 9:58 am   #20
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Default Re: My first foray into Old model TV repairs.

Thank you, I will have a look at them
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