Video Detector has a second function - Philips F6

[Maarten]

For the short time test, it won't overheat and it will help determine the problem. For the long time it might also be okay, but that should be tested.

[Andrew2]

Originally Posted by Kyle__B

It leaves a mystery: Why can I still hear everything when C524 is taken out?

Probably because the 5.5 MHz signal is at quite a high level and even without the 100pf coupling cap there's enough signal to make it work.

[Kyle__B]

Originally Posted by Nuvistor

The loud speaker is fed by a shielded cable, is there a possibility of a fault there introducing the hum into the circuit.?

None whatsoever. I've had the speaker out of the case while turned on, dragged the cable all over the chassis and yoke and it made no unwanted noises.

It only does it when the chassis is upright, with the neck of the tube poking through it's cutout, and where cables drape about makes absolutely no difference. You can put them wherever you want and they don't change a thing, so I leave them where the factory put them, which is why I said specifically not to bother me about that. It is strictly a problem that shows up when the neck/yoke and chassis are close to each other and nothing else.

Originally Posted by Andrew2

Probably because the 5.5 MHz signal is at quite a high level and even without the 100pf coupling cap there's enough signal to make it work.

Magic.

[Maarten]

A faulty cable is not the same as cable dressing, and while in my opinion not very likely it could cause interference. Even if it was in his right to do so as an unpaid helper, Nuvistor probably didn't mean to "bother" you.

[Kyle__B]

It doesn't much matter now as I've got the 4ohm version of the loudspeaker coming in the post. Solid state amps don't give me this kind of nonsense to deal with.

[Nuvistor]

I may have missed it in previous threads but have you proved it is the yoke that is causing the hum, easy test is alter the frame hold and confirm the hum changes frequency. If it does your are correct, if it doesn’t then something else is inducing the hum.

[Maarten]

Originally Posted by Kyle__B

It doesn't much matter now as I've got the 4ohm version of the loudspeaker coming in the post. Solid state amps don't give me this kind of nonsense to deal with.

I sense a bit of frustration. If you want to tackle electronics problems optimaly, a certain amount of "zen" is needed. When (not if) you encounter an unsolvable problem, that doesn't mean you're defeated. If people don't have the right advise for you, as it can be hard repairing something by proxy, it can be a moment to either brush up on relevant theory, go experimenting, or put it aside and do something else first.

Building something can be as frustrating as repairing, as transistor amplifiers are also totally prone to this and other kinds of nonsense, but you may get lucky.

As nuvistor writes, a simple method to determine whether the hum is frame related is to change the frame hold. Apart from shielding the valve, you could also try shielding part of the pcb. Something entirely different: how is the cathode decoupling electrolytic on the PCL86? Do the ripple voltages on the supply lines confirm to the schematic?

Or taking a step back: how loud is that hum exactly?

[Kyle__B]

Originally Posted by Maarten

Building something can be as frustrating as repairing, as transistor amplifiers are also totally prone to this and other kinds of nonsense, but you may get lucky.

I've done it a lot of times and the only problem I had was when I built my first one at age 16 I accidentally connected the transformer the wrong way around.

For this TV it's not even like I have to design anything, how to run a 4watt 4ohm mono speaker is a solved problem. I'm just going to use an off the shelf design that people seem to like. It can live in the space where the tuner used to be, a million miles from anything that could interfere. It's own isolated power supply, going to be great.

Originally Posted by Maarten

As nuvistor writes, a simple method to determine whether the hum is frame related is to change the frame hold.

I suppose in the same way you can determine if a plane's poor performance is weight related by reducing the gravity. How do I do that?

Originally Posted by Maarten

Apart from shielding the valve, you could also try shielding part of the pcb.

There's no room.

Originally Posted by Maarten

Something entirely different: how is the cathode decoupling electrolytic on the PCL86?

If that's C527 (100uf), absolutely fine.

Originally Posted by Maarten

Do the ripple voltages on the supply lines confirm to the schematic?

I don't have a scope. All I know is that our first adventure with this TV was replacing all the power supply capacitors.

Originally Posted by Maarten

Or taking a step back: how loud is that hum exactly?

That's kind of a "how long is a piece of string?" kind of question.

Please understand that I don't have any special sound measuring machine so I can only describe it in relative terms.

When the hum is there (which is only when the chassis is closed, putting the valves a hair away from the neck and yoke) it's a constant volume.

Unfortunately that volume is only a little quieter than I set the TV during daytime, and a little louder than I set it during night time.

[FERNSEH]

Nuvistor wrote: "Philips were known for some, shall we say, more unusual ideas but they usually worked extremely well."

And I reckon this circuit will work very well indeed. The push-pull audio output stage will deliver high level FM to the U480 module which will in turn receive effective limiting by the OA95 diode. The rectified FM signal is supplied to the 9.1volt zener diode which supplies a negative voltage to the BA102 vari-cap diode in order to retune the sound trap in U483. The frequency of the resonant circuit will depend on the strength of the FM signal.

DFWB.

[Kyle__B]

I would like to know what the "simple method" of adjusting a "frame hold" is, and while we're at it I'd like to know what a "frame hold" is too.

Google's answer has to do with computer video editing, which I don't beleive existed in 1969.

Likewise I checked the book referenced earlier in the thread and there's not a single mention of any such thing as a "frame hold".

Am I to understand that I've been told to fetch a left handed screwdriver? You could just tell me you don't want to help instead of setting me off looking for something that doesn't exist.

[Nuvistor]

I wouldn’t under any circumstances send you looking for something that doesn’t exist, just trying to help.
A search of this forum would bring up many references to “Frame Hold”, it sets the speed of the vertical scan and for Europe is generally 50Hz. This is the frequency supplied by the vertical output stage to the scan coils, synchronised to the incoming TV signal.
The presumption is the interference is coming from the scan coils, which could well be correct. My suggestion was to alter the speed of the signal sent to the scan coils, if this corresponds with a change in the hum that confirms the source. If the hum didn’t change frequency the hum must be coming from elsewhere.
The test would just prove that you were not being led down the wrong path in tracing the fault. I would rather prove than presume when fault finding, not always possible but it saves going down the wrong path.

[Kyle__B]

I understand the idea but I've never heard it being called "frame hold" before, so I had no idea what you meant. That terminology only seems to appear on this forum. What I usually see people call it is vertical hold or vertical sync. Maybe "frame hold" is what english people called it in the 70s and it's died out everywhere but here.

I have no idea how changing it on a fixed frequency CRT chassis could be done. Forum results are all about faults where it doesn't lock on, or does something else like vertical collapse, nothing to do with deliberately changing it.

Something like a VGA monitor would syncronize itself up to any signal coming in within a given range. A 90s TV new enough to have on screen settings menus would at least do the same for 50 and 60hz.

I don't know how a 1960s valve TV gets it's vertical frequency. I can't find any adjustable oscillator. I assumed it was deriving it from the mains, which I can't change anymore than I could change gravity.

So what am I being told to do?

[AC/HL]

Bear in mind that this is predominantly a UK forum, and that is the terminology that we use. Minor language differences don't change the theory though. Best advice would be to read up on analogue TV principles. Synchronising is in principle the same for any CRT device, just with different ways of carrying the information.

[Kyle__B]

That's not a remotely helpful answer.

A helpful answer would be something like "You can change it by twiddling pot R7something6" or "you could swap out such and such resistor".

I already know that my TV has a 50 Hz vertical rate, and I also already know that it will try and lock on to the beginning of every field. I don't need to go learn that.

You lot have told me to somehow adjust my TV so that it's no longer vertically scanning at 50Hz. You even said it's simple to do.

If it's so simple why don't you just tell me how to do it? I've asked multiple times and you all evade answering the question.

[ms660]

R919 is the vertical/frame/field....lock/hold control.

And still pertaining to the vertical/frame/field, R920 is the height/amplitude control, and so far as I can make out R909 and R911 are the linearity controls.

Lawrence.

[Kyle__B]

Originally Posted by ms660

R919 is the vertical/frame/field....lock/hold control.

And still pertaining to the vertical/frame/field, R920 is the height/amplitude control, and so far as I can make out R909 and R911 are the linearity controls.

Lawrence.

Oh my god, someone actually gave me a straight answer. Beers are on me but none of you can have one.

[ms660]

In the old days the customer user control for the frame adjustment was usually called the vertical hold control, the actual stage in the receiver was most commonly called the frame or field stage.

Lawrence.

[cmjones01]

Originally Posted by Kyle__B

I don't know how a 1960s valve TV gets it's vertical frequency. I can't find any adjustable oscillator. I assumed it was deriving it from the mains, which I can't change anymore than I could change gravity.

TV's don't derive their vertical sync frequency from the mains. They all have an adjustable oscillator in the vertical timebase. Like most oscillators, it's prone to drifting in frequency as components age and, sometimes in old sets, as the mains voltage varies. So there's almost always a control for adjusting the oscillator's frequency, so that it runs with a frequency close enough to that of the broadcast video signal to correctly lock on to it and provide a stable picture. This control is known as the vertical hold, frame hold, or field hold (or sometimes vertical sync or frame sync) adjustment. Sometimes it's inside the set, sometimes it's exposed as a user control usually on the back or very occasionally on the front.

Lots of things have different names in different countries and cultures. On an English-speaking car forum, you'd probably find references to 'bonnet', 'hood', 'muffler' and 'silencer'. Television is no different - the 'frame hold' name is absolutely standard in UK practice, so you'll see it frequently on this forum.

Chris

[Paul Stenning]

Originally Posted by Kyle__B

That's not a remotely helpful answer.

Originally Posted by Kyle__B

If it's so simple why don't you just tell me how to do it? I've asked multiple times and you all evade answering the question.

Originally Posted by Kyle__B

Oh my god, someone actually gave me a straight answer. Beers are on me but none of you can have one.

That attitude is not acceptable here.