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Old 25th Jan 2023, 8:04 pm   #21
slidertogrid
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Default Re: Pye CT72 Fire!

Back to watching Dr Who!
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Old 25th Jan 2023, 8:08 pm   #22
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Default Re: Pye CT72 Fire!

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Originally Posted by G6Tanuki View Post
That's worrying!

I'm kinda glad that the vast majority of my gear here has steel or aluminium cases which would contain any 'internal' conflagrations.
That's what reassures me about professional comms gear, too- it's quite conceivable that a waxed-paper etc. mains transformer could burn up (as did the one in my CR100 many moons ago....) but at least such an event ought to be confined better for longer than in a plywood box with a generously-ventilated hardboard back.

I once encountered thick black smoke and gawd-awful stink emerging from a Prowest "professional" colour monitor (17" low-focus tube), opening it up revealed that the black-case ITT tripler had spectacularly gone full Salvador Dali, slumping down from its place in the middle of the large vertical PCB into gooey stalactites and staying searingly hot for a worryingly long time after power-off and opening up. I assume that something had gone leaky within (multiplier ladder capacitor?), running hot enough for quite some time so as to melt potting compound and casing without being serious enough to cause the LOP series supply regulator to trip.

I've always been in two minds about potted components- yes, great if done properly for excluding dust and damp (and keeping proprietary secrets!) and pretty much essential with something like a TV tripler, but also hiding a few sins in terms of mediocre components, the failure of any one mandating a whole new module, and some rather hasty and sloppy interconnections- the sort of thing that left out in the open would earn one a justified bollocking, especially in the likes of mains filter modules.
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Old 25th Jan 2023, 11:13 pm   #23
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Default Re: Pye CT72 Fire!

The last burnup I had was last year, I had dragged out some 1990s Thomson TVs and after a brief test I switched one off and went the other side of the workshop. I soon smelled smoke and it came pouring out. Mains filter capacitor was to blame. I'm pretty sure (though not 100%) that this was located before the mans switch, hence the post-power down burnup.

I would like to think that a set that late was made with fire retardant materials but who'd want to take the chance? After all, a very similar 1990s-vintage Matsui set once caused a fire leading to the death of an elderly woman.
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Old 26th Jan 2023, 8:15 am   #24
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Default Re: Pye CT72 Fire!

I seem to remember the brown ceramic cap on the outside top left of the LOPTX failing with s/c, 180pfd or there abouts.
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Old 26th Jan 2023, 9:34 am   #25
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Default Re: Pye CT72 Fire!

Yes, some sets we saw over the years - Sony 2090 and Thorn 1615 are both well known. We had a couple of Korting solid states go up (plastic back almost touching a wirewound which overheated when the TV tripped). Bush 2550 and Salora M with serious damage, so this sort of damage wasn't confined to colour's early days.

LCD sets are pretty good, though we've had a couple of LED sets with serious overheating and damage to the screen when an LED fails.
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Old 26th Jan 2023, 9:43 am   #26
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Default Re: Pye CT72 Fire!

A very unusual fault and glad it did not lead to a more serious fire.
This is a cautionary tale for all of us that repair and run older televisions especially colour televisions.
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Old 26th Jan 2023, 1:28 pm   #27
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Default Re: Pye CT72 Fire!

An obvious point when restoring sets is to ensure good quality of replacement parts (i.e capacitors) and to ensure such things that insulation sleeves and wiring grommets on wiring to terminals haven't gone missing or crumbled away over time.

Obviously many sets were made before BS415 came into being so there may well be poorer construction standards than is satisfactory now. (mains switching, fusing, insulation material types and properties, creepage distances ect..)

Also worth ensuring like for like power rating for such items as resistors so that if a fault develops, a protection device would operate rather than a high power resistor in place of say a small or fusible resistor sit there causing heating of another component rather than failing itself.

I keep my sets on a wooden table or shelf and away from carpets etc.. so that the ventilation holes cannot accidently be covered up.

Christopher Capener
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Old 26th Jan 2023, 1:54 pm   #28
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Default Re: Pye CT72 Fire!

Can we please stay on topic two posts deleted.

Cheers

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Old 26th Jan 2023, 3:16 pm   #29
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Default Re: Pye CT72 Fire!

I suppose the problem isn't so much the more lax standards in the past rather that TVs weren't supposed to last this long - and, of course, the vast majority didn't.

I would imagine the grommet and the tripler's casing may well have become less fire retardent than they were when your TV was made around 1971.

Some hybrid sets did gain BEAB approval - the ITT CVC9/1 and the Decca 33 series spring to mind, though the Pye Hybrid never did.

I do wonder if your fire would have gone out with damage limited to the line tower, though of course I'm glad you didn't have to find out. Some self-extinguishing plastics certainly used to burn with really acrid sooty smoke but then ceased combustion.
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Old 26th Jan 2023, 3:20 pm   #30
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Default Re: Pye CT72 Fire!

Quote:
Originally Posted by high_vacuum_house View Post
An obvious point when restoring sets is to ensure good quality of replacement parts (i.e capacitors) and to ensure such things that insulation sleeves and wiring grommets on wiring to terminals haven't gone missing or crumbled away over time.

Obviously many sets were made before BS415 came into being so there may well be poorer construction standards than is satisfactory now. (mains switching, fusing, insulation material types and properties, creepage distances ect..)

Also worth ensuring like for like power rating for such items as resistors so that if a fault develops, a protection device would operate rather than a high power resistor in place of say a small or fusible resistor sit there causing heating of another component rather than failing itself.

I keep my sets on a wooden table or shelf and away from carpets etc.. so that the ventilation holes cannot accidently be covered up.

Christopher Capener
I don't think the fault can be blamed on a previous repair as the tripler was an original PYE type and the disc capacitor looks as if it is the original one.
I have replaced the triper with a secondhand original type that is a later replacement made by ITT. so it should be safe enough. I have also made sure the soldering in the little cups is round with no spikes that could encourage tracking. All the wiring is tied back as it should be.

All of that said it has to be accepted that the set is well past its original design and expected life, insulation may well be past its best. It certainly has made me more aware of possible hazards and I will never switch off old sets and then leave the house for at least an hour after switching off and a second check of the set(s).
I have been to Screwfix this morning and have purchased two new up to date smoke alarms!
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