Tech Chat Remember Name That Tune? Well, Lets Play Name That LOPT

Hi Chris I think some of the later replacement aftermarket LOPTs for the G8 looked like that. If you say the pinouts are different then they can't be both G8 I recognise the one with the dark red winding as G8 I will have a look in my box of spares I think I may have a similar one.

Really Rich? I'm shocked. I don't understand, so where is the EHT overwind, is it stacked in the main winding?

As for pin-outs, I've circled all the discrepancies I found, which along with no overwind, is why I thought no way a G8.

If they are later releases, without an installation sheet, I'd never fathom wiring it in.

Doesn't ring any bells with me at all and while I agree that other winding looks life a supply to an EHT rectifier it's odd that it's going to what appears to be PCB pins. You wouldn't want EHT on a PCB.

Edit as post crossed. Looking at the picture of the original G8 LOPT I agree it does look like a later after market replacement. The longer threaded bolts are the mounting points and what appears to be a heater winding is a pulse winding wound between the two bobbins on the original

As for wiring up I would suspect the connections may be the same compare ohm readings with an original, even a dud. There's a 50 50 chance with the pulse winding, if it doesn't work just reverse the connections to it

Thanks for that John, now I've sussed the wiring.

Hi Lads,

Yes the HR is definitely G8, I got one years ago for a G8 I had. Last about 4 years before it gave out although I was told they were way better than the original philips part.

In my experience LOPT failure on the G8 wasn't that common until the sets were fairly old. Then they started to drop like flies. If a tripler failed and the LOPT was the older type or the original the Lopt would often fail a short time after the tripler replacement. This wasn't just a problem with the G8 it happened with the solid state ITT CVC 20/30 and Decca 100 as well. When the 3000 / 3500 got old often a faulty tripler would kill the EHT transformer even the jellypot wasn't infallible. I never had a G11 lopt fail until the sets were old then the odd one would die, luckily by then there was plenty of scrap panels around as the sets would have been BER otherwise.

One of those is identical to the LOPT currently fitted to the G8!

This is definitely a Konig LOPT.

Oh, in that case the overwind I offered is totally not suitable as it's for the older type lopt

Posted by: @slidertogrid

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In my experience LOPT failure on the G8 wasn't that common until the sets were fairly old. Then they started to drop like flies. If a tripler failed and the LOPT was the older type or the original the Lopt would often fail a short time after the tripler replacement.

Aha! NOW it makes sense. The tripler failed and not long after I fitted the new old stock one @crustytv gave me the LOPT failed. Konig LOPT failures seemed to be rare/non existent but this G8 doesn't seem to have been stored in ideal conditions plus it must be at least 40 years old now.

@crustytv I also have this one which was in the bag of bits:

 I might just bring both of them to you on Wednesday and let you have a look as I'm confused now. 🤔

That's the type I'm used to seeing on a G8, not the other replacements which have the overwind stacked with main winding with the pulse winding on the other core.

By all means bring them over, we can put them on my LOPT/flyback tester. The device can test the entire television horizontal output section, including the horizontal output transformer windings (LOPT/flyback) and the horizontal and vertical windings of the yoke, if I had the whole set. Bringing the whole TV would be a nightmare for you and for me, as at present I've little space, having just taken delivery of a new TV.

However, as I say, we can test the LOPT on the board, in circuit testing (which this device can do) is the easiest to make and faster than having to isolate the LOPT or components, which my other LOPT tester needs you to do, likewise if you use a scope to ring.

Testing is simply selecting the range of ring tests A - F.

A "GOOD" indication by the meter will mean that the windings are okay and there are no shorts in any of the yoke or lopt/flyback windings. Oh, it can do valve and solid-state sets, which is very useful.

A demo below of the LOPT/flyback tester. In the second photo I'm testing the LOPT in circuit, as you can see it's good. I then wrap a single coil of wire around the overwind, to simulate a shorted turn. As you can see from the final photo the tester now see a short and the LOPT tests bad.

@crustytv that would be brilliant, cheers! I've done ring tests on the Rediffusion's LOPT using my scope prior to powering it up for the first time and the results weren't always conclusive.

How useful were ring tests on the later diode split LOPTX’s? I can’t say I every tried that.

I'd imagine not very much use at all. By the time of those types of LOPT's there were split diode testers available. Here's mine, I've used it for testing my stock of transformers for the TX90 & TX100.

https://www.radios-tv.co.uk/vintage-electronics-blog-forum/flyback-transformer-data-sheets/

https://www.radios-tv.co.uk/community/in-the-workshop/split-diode-lopt-testing-diemen-stvdst-01-flyback-tester/

Someone is trying to start an argument with me on Faceache about a 90s split diode LOPT in a Panasonic. It makes a high-pitched screech and the set shuts down. I just said it's not worth fixing unless you can find a replacement LOPT from the likes of Domberg.

There's the whole "it could be the yoke shorted" "it could be the power supply" "it could be this" etc idiocy you expect. 

I never bother with the Facebook queries. No one ever takes notice of what you tell them. 

Indeed, my time of FB was a real eye-opener, of course there are exceptions but for the most part it's the last refuge of the incapable. There's also a reason most of them stay away from forums, they get called out!

Oh, I've heard it all now:

"Wayne D You’re making a definitive claim of the worst possible situation based on little to nothing from OP. A high pitched whine could be several things besides the flyback, including, but not limited to, arcs to ground, bad coils, shorting caps that are beginning to squeal as they vent from the bottom, or even a standard 15khz whine from the set turning on and falling back into protect mode before the tube has enough time to warm up and produce the image."

🤣 shorting capacitors making a squeal! In my experience it's not the caps, it's anyone else who happens to be in the room when they go bang that makes the squealing sound...

Posted by: @crustytv

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There's also a reason most of them stay away from forums, they get called out!

I'd love to see even a couple of these idiots in here. Serious Face Man who argues with me regarding computer monitors and seems to think he's some sort of expert would last 5 seconds.