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Old 3rd Jan 2021, 1:25 pm   #1
ChristianFletcher
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Default My First Television Set Stella ST1017U

Hello All

I purchased an old Stella Television receiver a couple of years back from Goldborne. I remember it was supplied at little cost and the seller was a splendid gentleman who I think was genuinely interested to see the set going to a good home and to a vintage electronics enthusiast.He described the set as basically working but would require all the usual safety check and servicing before putting it back into service.

So I’m looking for some general advice on running the set up for the first time and what needs to be checked and changed. Note I have a lot of valve radio experience but none with television receivers so I’m interested in any special requirement and safety around the CRT.

I also plan on keeping a diary of the work in this thread including pictures but also plan on featuring my first and hopefully not my last restoration on my YouTube vintage electronics channel.

I think my first actually question will be what type of power connector does this use. I think given the sets condition I’m not too cornered about originality so was probably going to fit some form of IEC connector. However I may try to find a actual power connector on EBay etc.

I haven’t looked for service data as yet but if anyone could point me in the right direction that would be helpful.

I think my first step will be to vacuum it out and give everything a good clean while I plan my next steps.

Thanks regards Chris
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Old 3rd Jan 2021, 1:40 pm   #2
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Default Re: My First Television Set Stella

Not a lot to go wrong with these models. The Philips 17TG100U is the same receiver with just cosmetic changes.

Early reliable green 'mustards' so no problem there.

Things to check.

Strangely the mains filter and boost reservoir capacitors are the only ones that are not generally mustard types and if still the old black tar type will need to be replaced on sight.

The focus preset on the tube base, 2.2m drops in value decreasing the boost volage giving lack of height and generally slight lack of brightness. just snip the earth end off for test.

The 2.7m anode load resistor to the triode section of the PCL83 audio amp/output goes very high giving lack of sound with distortion. It's fed from the boost rail.

Poor frame lin is usually caused due to resistors going high in the oscillator/output stage or the bias cap going O/C.

The excellent Mullard AW43-88 will be 100% but the LOPT is prone to failure, especially after long periods of idleness.

Good luck with it. John.
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Old 3rd Jan 2021, 1:45 pm   #3
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Default Re: My First Television Set Stella

That a great start thank for that information brilliant.

Thanks John Regards Chris
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Old 3rd Jan 2021, 2:06 pm   #4
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Default Re: My First Television Set Stella

The LOPTs are definately weak. I had the Philips version once - the chassis was absolutely mint. The LOPT was dead. I gave it to a fellow collector who replaced the LOPT. Which soon failed. Another forum member had one as well, lopt was dead so replaced it. Which failed ! Both people I consider well versed in TV repairs.

So, definately worth passing some current through it for a few days to drive out any moisture and I'd be tempted to replace the LOP valve's grid coupling cap and also the boost cap so as to absolutely minimise stressing the LOPT.

TTFN,
Jon
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Old 3rd Jan 2021, 2:08 pm   #5
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Default Re: My First Television Set Stella

I want to clean around the picture tube and clean the grounding strap, will a damp rag be ok to use not sure if the the Aquadag will be damaged or come off.
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Old 3rd Jan 2021, 2:22 pm   #6
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Default Re: My First Television Set Stella

All sage advice from John and Jon. I would cleaning to a minimum before see "first light" just incase you disturb something. A lightly damp cloth should not cause any damage to the aquadag coating.

It may not be a bad idea to use a DC current through the LOPT for a few days to help dry out the overwind.
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Old 3rd Jan 2021, 2:44 pm   #7
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Default Re: My First Television Set Stella

I think I will have to give it a clean as it’s very dusty and setting off my Asthma. I also think it’s easier to make an inspection if stuff is clean.

I have some infrared lamps I use for warming up chickens and lambs could put one of those over it. It had been in the garage for a few weeks but been against a radiator for the last couple of weeks.

I was just looking are the circuit diagram and if I am reading it right the LOPT has a primary and secondary. Would I apply the DC to the primary. I think the manufacturers data may include resistance charts for the wound items so I’m wonder what current to apply or just start very low and wait until it warms etc. Not familiar with LOPTs. Also I have a CRT tester I’m itching to try out.
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Old 3rd Jan 2021, 3:27 pm   #8
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Default Re: My First Television Set Stella

Hi Chris,
That's a nice project- welcome to the wonderful world of TV repairs!

Don't forget, like almost all UK TV's, this will use the 'Live chassis' technique meaning the chassis is directly connected to one side of the mains. Could be the live or the neutral!

By definition, therefore you can't connect the chassis to mains earth. You must ensure the chassis is connect to mains neutral NOT the live.

You need to make sure you are aware of the safety implications if you are not already and that you can work safely.

I've come to expect grief with the LOPT on almost every set I've repaired whether or not they have a reputation for being unreliable or not. I always now, before powering up the set, pass a current through the overwind for several days or indeed week.

The idea is to get the overwind just gently warm. The current required will depend on the resistance of the winding and also the construction of the transformer.

This gives the overwind the best chance of survival but doesn't stop all the other problems. In fact, I've had more issues with insulation breakdown between windings and the core rather than failed overwinds.

However, there are plenty of ways of repairing LOPT's and I've not as yet had to resort to a full rewind!

Give the CRT a test by all means, but don't be surprised if it doesn't read much emission. Again, most of the CRT's on the sets I've repaired have read very low or no emission. They often recover once they have been run for a while. Trust me, CRT's give me far less trouble than LOPT's!! You have the same B&K tester as me and by many accounts they tend to read on the low side for emission.

Have fun with it!

All the best
Nick
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Old 3rd Jan 2021, 3:35 pm   #9
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Default Re: My First Television Set Stella

Hello Nick thanks for the kind words and encouragement I’m very excited to have my first television. Thanks for the reminder on the live chassis I have experience working with similar AC DC radio sets . I do also have experience working with very high voltage equipment although not with television. I am familiar with the obvious electrical dangers and have restored many oscilloscope and also some high power tube based linear amplifiers. I’m sure television have there own unique gotchas etc this forum’s great for that kind of advice.

I wasn’t sure what you meant by the over winding I can see it as a primary and secondary?

Thanks all regards Chris
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Old 3rd Jan 2021, 3:39 pm   #10
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Default Re: My First Television Set Stella

That is a beautiful looking TV set - I like the very minimalist look of it. My only experience with vintage CRTs is the AW43-88 and AW53-88, and even though they test poor on a Müter BMR7 CRT tester, they actually produce a fine picture with plenty of brightness and decent perfomance.

If you manage to scratch the aquadag (severely), I can recommend repairing it with "Graphit 33". It sticks well to the surface, if it has been cleaned well. I had to replace my AW43-88 due to an internal fault, and the replacement CRT had a severely damaged conductive coating.

Not knowing this chassis and make, but you apply a current limited amount of power to the "overwind" which is the one that has the anode cap for the DY86/87 or similar EHT rectifier diode. I think the LOPT is a two-bobbin design, so the "overwind" is a separate bobbin. I never understood why it was called "overwind", but I suppose other LOPTs the fine windings were wound on top of a single bobbin (?).
Anyway, a few watts through the winding for some days should suffice.
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Old 3rd Jan 2021, 4:24 pm   #11
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Default Re: My First Television Set Stella

The overwind is the winding which produces the EHT. A infrared lamp won't do as the moisture is deep within the winding. Connecting your bench power supply to the PL81 and DY? EHT rectifier Connections on the lopt and aim to disapate a couple of Watts from the overwind so it is warm to the touch. Over a few days this will drive out out moisture from within the winding. I wish I had known of this method years ago when I tackled my Pye V510.

This is now the first thing I do when tackling a TV of this vintage.
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Old 3rd Jan 2021, 4:50 pm   #12
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Default Re: My First Television Set Stella

Lucky you, I have the Philips version, it was full of the black tar caps which were changed. From memory a few resistors were reading high which after changing gave a good picture. While cleaning all the valves I found a pin on one valve with a kink in it which I foolishly straightened, this resulted in no sound. After some head scratching the penny dropped the kink put back the sound returned. It must be one of the easiest sets to service with the chassis swinging out like a door.

Good luck with it, John.
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Old 3rd Jan 2021, 5:54 pm   #13
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Default Re: My First Television Set Stella

Thanks everyone I understand now regards the overwind I will measure it’s DC resistance and as you say arrange for a couple of watts of dissipation and check it’s temperature. Just noticed that apart from Nick everyone is called John will I have to change my name it must be a TV thing LOL thanks.
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Old 3rd Jan 2021, 6:25 pm   #14
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Default Re: My First Television Set Stella

I have the Philips 17TG100U, same set, different cabinet.
As others have said, the LOPT is a weak point on this chassis, however, mine has given no trouble at all.

I only needed to change the black tar caps, especially the boost cap, the green Mullard caps were tested and proved to be fine.

These sets do produce one of the best pictures of any 405 line receivers once sorted.


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Old 3rd Jan 2021, 8:55 pm   #15
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Default Re: My First Television Set Stella

Thanks mark that sounds encouraging. Regards Chris
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Old 4th Jan 2021, 9:51 am   #16
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Default Re: My First Television Set Stella

Hi Christian
I Just picked up on Thread. I see that all the other's have given you
lots a good advice regarding this very nice set very easy to work on. I do not
remember the loptx being a problem on this set , but it is a long time ago when I worked on these. The focus slider on the crt base was a bit hard to locate at first , but once found faulty it was a very common fault.When testing
make certain that the anodes of both PY82's Have A/C on them if not the set with try to work with low ht.also test the thermistor in the heater circuit (grey component with yellow lead connected to it ). If stages did not cause and problems , but like all Tv.s of that time low gain would be due to the rf amp PCC84 in the tuner. Looking forward to you getting it working . hope you learn a lot about tv on your first 405 line Tv
Kind regards
Derrick ( middle name is John)
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Old 4th Jan 2021, 1:21 pm   #17
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Default Re: My First Television Set Stella

Thanks Derrick

If I’m reading the circuit diagram correctly bathe CRT focus control is on the back of the CRT and for some reason it looks like one of the legs on the slider potentiometer has been cut. Maybe to increase the voltage. I will need to investigate this further. Thanks for the heads up

Regards Chrisv
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Old 4th Jan 2021, 2:19 pm   #18
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Default Re: My First Television Set Stella

Yes I have a few TV books on the go at the moment but I’m probably only understanding about one word in three, but I guess one has to make a start somewhere. I have repaired quite a lot of old oscilloscope so some of the circuits are common to TV receivers but it does feel very daunting with a lot to learn. I’m guessing like eating an elephant, it’s small bites etc. I noticed that I posted a pinned question about efficiency diodes back in 2006 so it’s only taken 14 years to pluck up the courage to have ago at a TV LOL
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Old 4th Jan 2021, 2:20 pm   #19
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Default Re: My First Television Set Stella

Quote:
Originally Posted by ChristianFletcher View Post
Thanks Derrick

If I’m reading the circuit diagram correctly bathe CRT focus control is on the back of the CRT and for some reason it looks like one of the legs on the slider potentiometer has been cut. Maybe to increase the voltage. I will need to investigate this further.
IIRC this is how I found my set. If I get a chance I will check later.

John.
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Old 4th Jan 2021, 2:26 pm   #20
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Default Re: My First Television Set Stella

Thanks John
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