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

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Old 27th Oct 2017, 2:17 am   #81
Argus25
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Default Re: My first antique TV-Olympic Model 755-need help.

American RF coils in TV's are often quite different to English ones. In American sets there are often threaded brass screws attached to the ferrite slug with a thread and locking mechanism on the coil top.

In many UK sets, there are ferrite slugs in bakelite former . In the case of these never attempt to turn these with anything other than a plastic instrument. Apart from the fact a metal instrument de-tunes it, the metal vs ferrite contact puts extreme focal forces on the slot in the slug, and it will crack.

If it is just the very top near the slot that cracks, usually you get a second chance from the slot on the other side of the slug. If however the slug splits in two, it won't unscrew as it expands in the hole with any attempt to rotate it and the cracked edges bind in the thread.

Drilling out one of these slugs is not practical as the ferrite wont drill, the drill will simple decenter and damage the threads/former. It could be possible to use a diamond grinding tool. So if these slugs are jammed or tight, avoid to much force and use a combination of warmth to soften wax and melted rubber and wd40 to gently get them moving and only with a plastic tool, never metal.

One way to lock the ferrite slugs is teflon tape, but originally they often had a small rectangular section rubber cord, maybe only around 0.2mm to 0.3mm square. The trouble is this stuff melted or disintegrated with time, it was probably latex.

There is some fine white small diameter rubber cord available, it is found in flat elastic used in the waste bands etc of clothing, so you can get it from any sewing shop. You have to pick off the white fabric around it to get the thin white rubber cords out, it is perfect for locking slugs in UK style RF transformers.
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Old 4th Nov 2017, 2:24 am   #82
ct92404
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Default Re: My first antique TV-Olympic Model 755-need help.

Hugo, I got the "Basic Television. Second Edition" book!
I just finished chapter 4, and I'm already learning from it. Some things are starting to make more sense. There are some things I'm a little confused about, but I'll ask about that in another topic.

1100 man, I think I have good news about the transformer too. I was testing the tv intermittently and then I had it powered up for a little over a half hour. Probably altogether it was powered for close to an hour. I touched the transformer (with the tv OFF and unplugged, of course!) The outside winding, which I"m assuming is a high voltage secondary winding, was barely luke warm. The winding closest to the core, which I'm assuming is a primary winding, was hot, but not so hot that it burned my finger or I had to pull my finger off right away. I would say that it just felt a bit "uncomfortable" but I could leave my finger on it without getting burned. I wish I had a more accurate temperature! I've felt other transformers getting super hot just under normal use, so I don't think it's overheating.
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Old 4th Nov 2017, 10:12 am   #83
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Default Re: My first antique TV-Olympic Model 755-need help.

Hi Chris,
Transformer temperature sounds pretty good to me. Anything lower than 'ouch' hot is a good result!! I have even mounted small cooling fans to blow air over particularly hot running LOPT's in the past: makes a big difference.
I bought myself an infra red 'point and shoot' type thermometer from Ebay for about 8. It's great for measuring LOPT temperature and I think it will even do Fahrenheit
It's good to see you're interested in finding out more about how TV's work. Only problem is, the more you find out, the more you realise you didn't know!!
Cheers
Nick
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Old 4th Nov 2017, 10:39 am   #84
ct92404
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Default Re: My first antique TV-Olympic Model 755-need help.

LOL yeah it was like "ooh...that's pretty hot," but not "OW! Holy crap that's hot!"

Also, I have soft skin and get burned easily...which I was reminded about after a couple of mishaps with the soldering iron!

The fact that my poor little finger didn't get burned I guess is a good sign that the transformer isn't overheating. I'll keep your idea of a small fan in mind though. I might get one of those thermometers you mentioned too. I'm surprised you got it for that price, I assumed those infrared thermometers would be a lot more expensive. And yes I'll take it in fahrenheit, thank you very much!
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Old 4th Nov 2017, 3:15 pm   #85
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Default Re: My first antique TV-Olympic Model 755-need help.

As a very rough guide to temperatures I've found that at 40C(104F) you can keep your hand on the transformer without feeling the need to remove it. At 50C (122F) you can keep it on but will want to remove it after a short time and at 60C (140F) you'll want to remove it fairly quickly. Above that you won't want to touch it and risk burning your hand.

From what you say it sounds as if the transformer is OK.

I have one of those IR thermometers and they will give a good indication of the temperature but you do have to be careful as the cheaper ones are set up for a single value of emissivity, usually equivalent to a dark surface. A shiny surface at the same temperature would give a different temperature reading. More expensive ones, such as the Fluke we had at work, would allow the emissivity value to be changed. But at that price you can't really go wrong.

Keith
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Old 8th Nov 2017, 8:46 am   #86
ct92404
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Default Re: My first antique TV-Olympic Model 755-need help.

Success!! I got the sound working! Now I have a good picture and good sound!

I decided to take a chance and very carefully adjust L2, L3, and L5. I turned each just a tiny bit at a time until the buzzing turned into a soft crackling sound. Then when turned the adjustment screw for L5 a little back and forth to try find a good spot, the sound suddenly came to life. I adjusted the fine tuning, and it sounded clear.

Both the picture and the sound are now coming in strong and clear on the same channel! (Channel 3). I finally did it! It took me a little over a month, but I got the tv fully working!
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Old 8th Nov 2017, 2:07 pm   #87
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Default Re: My first antique TV-Olympic Model 755-need help.

Wonderful! Next?
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Old 8th Nov 2017, 7:32 pm   #88
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Default Re: My first antique TV-Olympic Model 755-need help.

Very impressive performance - you must have the magic touch - many of us who claim to know a lot more about this stuff have struggled on occasion for months or years - well done
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Old 9th Nov 2017, 5:52 am   #89
ct92404
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Default Re: My first antique TV-Olympic Model 755-need help.

Thank you!
I think I just got REALLY lucky. The tv was in fairly good physical condition, and looks as if it had been kept in a dry place indoors. There was very little rust or corrosion. None of the tubes were bad, all the coils were good, and the high voltage transformer and CRT were good. All the critical parts were intact. Now that I know how insanely complex TVs are, I realize that there are a million things that could go wrong. Thankfully, it mostly just took replacing common, off-the-shelf parts (capacitors and resistors) and making some adjustments to get this one working again.

For me, it was a LOT of work to get the tv going again. It was one of the hardest projects I've ever done. But after seeing the major restorations other people here have done on vintage TVs, I think I was lucky for everything to have gone so smoothly. Pretty much every time I worked on it, I was rewarded with slight improvements in how the tv functioned. The frustrating setbacks I had in the very beginning were mostly just due to me mistaking certain parts, or something being out of adjustment.

It was hard, but actually fixing this antique tv and bringing it back to life has given me enough confidence that I think I could tackle another one sometime. Although if I ever do get another vintage tv, it will definitely have to be one that's a lot smaller and not as heavy! This tv may not be as huge as some others from that time period, but it weighs a ton!
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