Sonic'

After a bit of help really

Got a 32" Widescreen TV, and the litttle lad was the other day repeatedly hitting the screen with a small plastic toy (I didnt see this happening as I was at work) so unsure whether it was anywhere on the screen or repeatedly in the same spot (or small area)

Anyway the TV went off and a bit of smoke came out from the front, and the usual rather rancid burning smell that electronics equipment gives off 'when fried'

Is this possible that just by hitting the tube it can break it?

Now I have taken the back of the tv off, and checked a few things out, and I noticed an internal fuse has blown (the one directly from the mains lead)

It is a 250V 1.6A fuse, and I replaced it with one of the same rating (got shedloads of them in the garage) and then plugged the TV in and turned it on (still with the back removed) and the tube went to come on (usual surge, when turning the TV on) and then went straight off, the fuse had blown again

And again followed by the rather rancind smell again, so everything unplugged I traced where the smell was coming from, and it is a module full of capacitors of varying ratings and sizes (mostly small ones) a largeish heatsink, with what looked like voltage regulators on either side, this module also contains the external speaker outputs, and provides the signal to the internal speakers, and the module itself has a warning on it saying 'Warning 20V'

Anyway, ive put it all back together and left unplugged etc

Now what I would like to know, is it the Tube that has gone, or possibly a capacitor or something similar that is causing the internal fuse to go

The TV is approx 10-11 years old, and still has (or rather had) a fantastic picture for its age, but the last 12 months or so has seen some hammer from the kids, including throwing water all over it about 12 months ago, which only resulted in a blown capacitor, and cost me 40 quid to have taken away and repaired, and they fixed the east west too which reset after the millenium

the kids usually have a tendency to repeatedly turn the TV on and off in very short spaces of time, and i know this cant be good for the tube

So is hitting the tube the likely cause of the damage, or has it just been coincidence and the tube died of old age?

I know it probably isnt worth repairing unless again only a blown capacitor etc, and I doubt I would be able to claim on the house insurance either

Any help would be appreciated, and if it is likely it isnt the tube, then I will get it booked in to be looked at

Steve

P1Drifter

iTrader: (7)

make make and model is it ? to damage the tube your kid would have had to of hit it pretty hard, i would of said the tube is probably not at fault here and its something else.

Fuzz

Before getting the TV repaired...

Train your bloody kids.


Andy

Sonic'

LOL Andy, I know, they do know better, well most of the time

Its a Thomson and the number on the back reads

81 DXG 69 DL, other than serial numbers, this looks like the main model number

He may well have hit the tube quite hard, there is also a very tiny chip in it, on the surface of the tube, which happened when he threw one of his toys at it a while ago, but he is only 4, but then again is incredibly strong for his age

Shark Man

The most likely failure from vibration/hitting is a bad solder joint(s) on one of the PCBs, if on a critical component (say, voltage regulation cicuit - which is highly important with CRTs), it can cause a chain reaction and overload and blow up other components (thus the burnt smell and blown fuses).

The thunk of the degauss coil on switch-on shows at least part of the TV is working and a glimmering hope of repair, and from what you say it seem the fault may lie in the control/audio part of of the TV (usually on a separate PCB to the CRT control PCB? ). Very rarly does the tube itself fail. However, failure of one of the drive components for the tube is common, worst case is the flyback transformer which will render most CRTs scrap these days. The only way to check if the main part of the TV is ok is to power it up from a externl power source with a restricted current flow and eliminate the suspect control/audio PCB. So is not really a task that can be done at home without an inkling of what to prod and probe.

Here's some info: Notes on the Troubleshooting and Repair of Television Sets

And a stern word of warning, that "20V" maybe "20KV" as in 20,000volts and yes, this can get stored in good capacitors, and they trust me, they hurt...alot. If you can't discharge the caps don't go prodding. Leaving off it for a week won't work either - some info is on the above link (somewhere).

Some TV repair shop (if you can find one these days) may cahrge a flat rate diagnosis fee to give you a quote, last TV I had done (dead flyback) cost £20 to diagnose, Unfortunately a new transformer was £150 all-in, so I let them dispose of it and bought a new one.

Just to add, some Thomson TVs have very good circuit schematics in the back of the owner's manual. Quite handy for trying to identify which PCB does what purpose.

Regards
Kingpin

***I don't sell TVs, nor do I fix them, but I can get cheap LCD monitors, get your car serviced, supply car alarms, sort out those car park fender benders, build you a house and provide management solutions for small businesses. Does this affect the advice I give? I dunno, ask Sigma Sam ***

Sonic'

Cheers SM

This module, had a single wire going to the board that the tube attaches to at the back of the TV, just having a quick glance over that link you gave me, quite interesting stuff

One thing I did notice when I turned on the TV with the cover off, was what looked like a few blue sparks coming from the back of the tube, not quite arcing, although it could well have been some short arcing

Dont have the manual to hand for the TV, but I think it may well have a few diagrams in the back of it

Last time it went in, it was a 40 quid diagnosis, including collect & return (if not dead) I might take a few pics of the module tomorrow

CRAIGFIN

If its 10-11 years old, its had a decent life span. I wouldn't have much confidence in an electrical item that keeps going up in smoke. For safetys sake, get rid and get a new one.

I wouldn't take the risk fixing it.

Sonic'

Craigfin,

It doesnt keep going up in smoke, it did it once when the fuse first blew, when I changed the fuse tonight, it didnt smoke,

I know the TV is 10-11 years old, but the picture on it was still fantastic, especially for its age,

it never even got switched on for 6 months a few years ago, and for at least 3 or 4 years it only got switched on and watched for Formula 1

I used to spend a lot of time working away, and hence the TV never got used, so in reality out of those 10-11 years, it has only probably had about 3 years of 'normal' tv useage

The advent of kids, that useage has gone up dramatically over the last couple of years, but even so, apart from weekends, its still only on for a few hours in the afternoon

and unfortunately I just dont have spare cash to just go out and buy a replacement TV just like that, the kids can go without TV for a while, and maybe they might learn not to break it anymore

dharbige

Do you have Accidental Damage cover on your home insurance policy? That normally covers this sort of thing.

ru'

[quote=Shark Man;6800151]...And a stern word of warning, that "20V" maybe "20KV" as in 20,000volts and yes, this can get stored in good capacitors, and they trust me, they hurt....quote]

Heed this warning; the high voltage used for TV tubes can really ruin your day.

Leslie

Sounds as though you have got a short somewhere, either a component or even internally in the CRT. If it is the CRT then you might as well bin it. It has done you pretty well anyway. PSL will give you lots of good advice on a replacement!

Les

Diesel

Ther vacum tube doesnt really 'go'.

Cant really work it out from your description - take a pic! Sounds like it may have something to do with the line output transformer drawing a lot of current if there is arcing and fuse popping. Could be quite cheap and NO, dont enter a disposable culture! CRT's rock!

D

andy97

iTrader: (1)

Your kids hitting the tv, has probably exposed a soldered dry joint issue, which would of happened sooner or later, sooner with your kids thumping the screen.

If the mains input fuse is blowing then the fault is most likley in the power supply section of the tv (converts mains AC into various DC voltages to feed the relevant tv sections).

You will need a tv engineer to diagnose the components that have failed. Power supplies in tvs are complicated switched mode operation (operating a high frequency tuned oscillator) and can damage various bits when they fail.

Andy

former tv engineer for 19 years

Diesel

It is a brave [or foolish] man who challenges 19 years of hands on experience, but I would have thought it a component/circuit AFTER the PSU that causes the problem? PSU issues usually result in no funcion/click/fizz output or hearing the fzzz of the shadow mask or degausss circuit on switch on?

D

Sonic'

Looks like it will be tomorrow now when I can get some pics lol

Cheers for all the advice, I *do* know that it will need a TV engineer to take a look at it, and not something I can fix myself, I really want to know if I am wasting my time having it looked at

I *do* know about the capacitors holding charge too, and how dangerous they can be

I cant remember off the top of my head now, where the relevant ribbon cables etc go after the mains comes into the tv, I do know where it comes in (where the fuse has blown) is a small pcb, encased in transparent plastic, with a small transformer, the odd capacitor, and one or two other small components

I will get some pics up tomorrow eveing tho, for those experts amongst us
so I can show where the smell is coming from )right behind a large heatsink on a plugin module (which primarily looks like the audio feeds for the internal and external speakers) but one small thin blue wire heads off up to the pcb the tube is attached to (the one with the gun adjustments on)

Steve

andy97

iTrader: (1)

If the mains input fuse is blowing, the two primary cuases would be the degauss circuit or the power supply itself. Generally power supply sections will go into protection mode and reduce the current and/or voltage to the rest of the tv if a fault is further in the set. If the mains fuse blows then then it would likely be one of the two causes listed.

Unless you have bought a cheap tv, with a crap protection power supply design and then virtually any fault will cause the power supply to blow aswell as the original cause of the psu blowing.

HTH

Andy

Sonic'

Ok, got a few pics now

The first one, the red highlighted area is where the fuse blew



The second the highlighted area is where the smell is coming from (behind the heatsink), it is unplugged in the pic which is why it is at a funny angle



The last pic, Ive highlighted two areas, as this is where the slight blue arcing/sparking came from, although I cant remember which area it was I saw it, and havent plugged it back in to try and test



the TV wasn't cheap when I bought it, there was only that one and the Philips Widescreen TV's that were available, but that isnt to say it was a cheap tv lol


Steve

Diesel

I think Anndy's yer man here, but in pic 3 the arcing is most likely to come from the EHT [v high voltage] thick red wire somewhere - check it for connections/damage/burns [has that degauss wire melted into it?]. Remember that when you pull it out of the glass of the CRT it may have a high voltage [v low current] still present so rubber gloves would be the order of the day and it should be discharged to earth [run the camcorder in case of a £250 Beadle opportunity]. The scan coils [that you circled] are low voltage and shouldnt really arc. Many options in reality really - sorry.

D

Shark Man

Ok, looks like the main power supply board, this is separate to the main flyback transformer, but does feed power to it, inside that there is a small keep alive transformer (for standby operation), and a few large ceramic resistors, there should be nothing much on that PCB that would cause problems. But obiviously an overload upstream of this would cause the fuse to blow.




Yup, big heatsink is usually for the power amplifier for the audio to drive the speakers, so this PCB is responsible for audio, although many modern(ish) TV may use the same PCB for other purposes, so it maybe responsible for video processing, tuner, or remote control operation. Seeing this board seems to house the input/outputs on the back of the TV, you can note its purpose by just looking at what connectors are soldered to it (speaker connectors, phonos etc). Blackened areas and components are a good sign of dead components, be be aware that componets that do get hot (such as the power amplifier transistors) can cause burning and browning of the PCB and even blisters on teh components themselves yet can still normally operate, not to mention attracting dust. The key to note the difference is noting if they are soot deposits from a quick exposure to intense heat giving layer of black carbon as opposed to brown heat stains and dust from sustained heat over a long period.

I also note that this board has speaker level connectors as used with many audio amplifiers, if speakers were connected to these and too much insulation was exposed (either from too much insulation stripped off or a wire being half pulled out), the disturbance of the TV (from "minor" abuse ) could cause wires to cross and cause an overload. I would however expect to see the TV resume normal operation once the short was removed and fuse replaced, abielt with a dead power amplifier (no sound). Although an overload could cause a component to permanentally short. So this maybe not the problem, but something to keep in mind.




The left circuled area is is common to get static dicharge between the windings, it shouldn't do it, but as the TV ages it can, and those sparks should be consitstent with a cracking static type noise you get everytime you turn the TV on and off. The right circled area contains the electron guns this can glow as it contains heaters, but it should be a glow like a small lightbulb.

Abdabz

Lugsmore Lane, my friend, the shop at the top by Taylor Park / Prescot Road... I'm sure you may have someone local in mind, but if not they might be worth a try.
I once used a mentallist from Duke Street to look at repairing my old 32" phillips which I bought in 2000 and only lasted 3 years, but he just dribbled on it and said it was "broke"...

Sonic'

I cant see any visible signs of soot deposits, or anything that looks out of the ordinary, cracks in the ceramic capacitors etc, there are around some of the components on the back of the tube, what look like to be iron filings for want of a better term, but I expect this is normal for a TV of its age

The back of that module only has the speaker outputs, and no speakers have been plugged into it for about 8 or 9 years

Behind the heatsink are a rather large number of small purple capacitors, again none of which look 'blown' or damaged in any way, but this is where the smell is coming from, behind this area

one blue wire goes from that module upto the Tube PCB, and it has a number of other connections off to the internal speakers, and has two strip connectors (about 8 on each) where the module plugs into the mainboard, the Modulators etc are housed next to this module on the main PCB

The Video inputs are on the main PCB, and the phono inputs are on a very small PCB attached to the side of the TV casing

I think this is what is more than likely was, and it did only happen for a brief moment, and you can hear the degauss side of things going


Abdabz, IIRC it was Duke Street who sorted the TV out last time, after being soaked with water whilst switched on, one replaced capacitor and fix of east west, job done, all for 40 quid

I couldnt get through to lugsmore lane last time, but may try them this time