My TV has died!

There's probably a million and one things that could be wrong but I just wondered if anyone could hazard a guess why my portable TV is dead. It's a Grundig 15" cobi tv/vcr twin tuner which is around 10 years old, so may well have died of old age. It was left recording but later noticed there was no power or standby light. There's power from the plug going into the tv. Had a look inside and noticed the main fuse had blown so replaced with identical T1.6 from maplins. A continuity tester showed power was now flowing around the circuits when switched on but still nothing happening on either the tv or vcr. I'll probably scrap it but thought I'd ask just in case anyone knows of any common problems with this model that may be worth having fixed?

Reply to
Redwood
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Or post same to sci.electronics.repair but quote the model number!!!

Reply to
Adrian C

I'm not quite sure what you mean about "power was now flowing around the circuits" - do you simply mean that there was a finite resistance between live and neutral, rather than an open circuit?

As a pure guess, something - maybe a diode or capacitor - in the internal power supply has blown, causing the fuse to blow. Locating and replacing the faulty component may well fix the problem. If you can do it yourself, it may only cost a few pounds - but it may not be economical if you have to pay someone else to do it.

Reply to
Roger Mills

Check the power supply PCB joints for any dry joints by using a tooth brush dipped in meths and scrub over the area of the power supply,this will reveal any dry joints ie the solder will go grey and if a dry joint is present it'll show up as a dark/blac cracking or use a magnifier.

If you're not savvy with electronic stuff then bin it although it is a TV/VCR these are worth more than the TV/DVD Combis.

Reply to
George

Ya got that right, I've ust been down to my local TV&Radio spares shop which I have not been to for nigh on ten years and I knew the bloke very well.

I was disheartened when he told me he's closing down as his over heads is crippling his profits because the electronic consumer goods repairing has diminished considerably as no one wants to pay for the repairs of TV's Video's,DVD's.. ect.

I blame it on todays throw away society.

Reply to
George

How conductive is flammable meths applied over a rectified mains recently charged reservoir capacitor? The latter should be safely discharged before attempting this.

Reply to
Adrian C

Erm! I've been doing it for over 25 years and never had a fire yet nor a short on TV's,the meths dry out very quickly.

Reply to
George

A bit like todays standards of literacy.

I blame it on the parents.

Reply to
Man at B&Q

Yep,in your case they reared an asehole.

Ah didums, what did you fail at in scool?

Reply to
George

I rest my case.

Reply to
Man at B&Q

I rest my case.

What ya mean School and Aw?

You can't even spell necessary,its spelt with one 'c' not two

Reply to
George

snipped-for-privacy@8g2000hse.googlegroups.com...

And its should be it's

Stop digging!

Reply to
Man at B&Q

messagenews: snipped-for-privacy@8g2000hse.googlegroups.com. ..

And its should be it's

Stop digging!

Stop being a pedant.

Reply to
George

I did have a fire once using 'cfc free' electrical spray cleaner. I was using it to clean a switch carrying only 28volts, when I noticed the flames.

Reply to
<me9

Reminds me of the time I was on the Manx ferries.

One of the deckhands was all set for a night out on the town. Had a ciggy in his mouth and started spraying cossack hairspray on his bonce,ended up with no eyebrows...that put paid to nights out for awhile. ;-)

Reply to
George

snipped-for-privacy@l42g2000hsc.googlegroups.com...

Learn to quote correctly.

Reply to
Man at B&Q

Guessing, I suspect that the ohmmeter reads fairly close to short-circuit and the fuse has blown violently, and that a replacement fuse suffers the same fate. It's worth sacrificing one more fuse to confirm the hypothesis. (Alternatively use a service technicians' trick and connect the set to the mains via a 500 W halogen lamp to act as a current limiter / fuse saver.)

IME the most likely component to have failed will be the 'chopper' transistor in the SMPS - usually a power MOSFET these days, and probably a 3-legged TO-220 device which can easily be unsoldered and tested with the multimeter for a source-drain short. If this is the case then carefully check the snubber network for o/c components or joints, else you may instantly lose the replacement transistor.

Other possibilities are a s/c RFI filter capacitor in the mains input circuit, or one or more of the diodes in the mains bridge rectifier.

Yet another possibility is the PTC device ('posistor') in the degaussing circuit. This is easily disconnected and of course there's no harm in powering-up a set with the degaussing disconnected, as a test.

Of course a service manual, or at least a circuit diagram is a great help in finding your way round.

Reply to
Andy Wade

Thanks for all the replies and links. I had another quick look today and using a DVM I tested for voltage across the new fuse that I replaced inside the tv. I noticed that when the fuse is in place there is no voltage showing at either end of the fuse holder terminals - however if I remove the fuse then there is mains voltage going to one end of the fuse holder but when I refit the fuse there is no voltage again. Although there is no power flowing across the fuse, using one of those cheapo continuity testers that glow when detecting mains voltage, if I hold it within a foot of the tv when switched on it glows fairly bright when pointed all around the tv - and if left unplugged for a while and then switch on I do hear a slight noise like it's recharging the tube or something? Not sure if this narrows things down any but I think I've gone as far as my capabilities allow on this.

Reply to
Redwood

I think the last sentence is correct. Sorry to be a bit of a damp squib, but...

This is a joke, right? If not, then replace the cover on the TV now.

"Voltage across the fuse"? Of course there is none if the fuse is good, the fuse is a bit of wire! Of course there is mains voltage with the fuse removed! That's correct and normal.

"No power flowing across the fuse"? I'm sorry, your understanding of how his works is clearly far below the danger level here. Put the cover back on.

The cheapo continuity tester glowing in close proximity indicates the main PSU is up, the Line Timebase is running, and the EHT multiplier is running. You have around 25,000 volts on the tube anode, ( also the cause of the power-up crackling noise ) and you have no clue what you are doing. You are in severe danger of having a very bad experience. Under no circumstances come anywhere near the fat wire which comes from a 'sucker' on the top rear of the picture tube, and is held in plastic wraps well away from everything else. It contains the 25,000v I mentioned.

Put the cover back on. Now. Please.

Reply to
Ron Lowe

Excuse me Ron but I do know that a tv carries around 30k volts and I have no intension of going anywhere near "the big fat wire" or capasitors. I do realise that a tv is the 2nd most potentially dangerous equipment in the hosehold behind the microwave.

Reply to
Redwood

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