Hi new here, CRT TV question..

[ziggatron]

HI I have a CRT TV that I am trying to repair, it is my first CRT TV that I have looked at.

I have just finished reading how to diagnose and fix everything electronic, which was really excellent and I got hold of this donor TV to attempt my first CRT TV repair.

Would have liked to work on a LCD etc but could not get a donor.

Having removed the rear panel, I powered up the TV and there is an obvious short, i.e sparking and smoke in a pretty larger component which feeds directly into the tube.

I have supplied pictures.

I wondered if you could help me to identify this shorting component and maybe offer any opinions to the possibility of repair. (the third pic circled in red - sparking inside the component, close to the tip of the marked red arrow) (is this some type of inductor or transformer? Actually looks vaguely similar to a HT lead coil on a motorbike..or is that just my imagination

I know the TV has little residual value these days, but this is as much a process of learning as it is anything else.

I would like to take the main board out to clean all the dust and gunk off it and to have a better look at it but I am wondering about the many large caps (on the AC supply side) and whether they will still be holding a charge, particularly if the TV doesn't work and there has been no load placed on them.

Caps pictured in pic 4 circled in yellow.

I don't have resistors lying around here and I was wondering what your advice would be.

The TV has been unplugged for a few days now, but as I understand it, thus can mean very little in terms of the caps being discharged.

Thanks for your help.

 

[GreenGiant]

The caps should be fine by now but as alwaus with CRT's be careful of everything that you touch, you dont need a resistor for the caps just a metal rod to short the leads, that'll do it.

The component that is sparking is the flyback transformer, it is integral to the operation of the set, its basically what powers the tube, you will need to buy a replacement one, other than that there's not much you can do.

 

[shrtrnd]

And that flyback generates over 20,000 Volts. so watch it.
The anode plug from the flyback to the plug on the picture tube will have a few
thousand volts on it even when the TV is turned-off and unplugged, stored energy
within the picture tube itself. so watch that.
If you find a replacement flyback for your model, it'll probably cost you more money
than you want to pay for it, ... but who knows what you might find.
In any event, if you continue with this, be careful. You're working with the most danger-
ous part of the old CRT TV's: the high voltage section.

 

[ziggatron]

Many thanks for the replies, I have just read them.

Wondering why I received no email notification of the replies actually? I left the default post reply setting as "instant email notification", maybe some one could shed some light, as I would like to know as soon as any replies are posted...

Thank you for the i.d of the component and the warnings..

Is it ok to short the caps in situ?

I am thinking I will use a standard house light bulb.

I have heeded this warning..

"" While it is also possible to use a small screwdriver to connect the capacitor leads, the amount of current discharged may melt the screwdriver's tip or the copper on the circuit board if the capacitor is still connected to it. Particularly large sparks can fry power supplies or turn melted copper or solder into a projectile that can injure you.
Large capacitors are extremely dangerous and others are often in the vicinity of one you might attempt to work on. Working with them probably isn't best for a typical hobbyist.""

@greengiant
@shrtmd

""The anode plug from the flyback to the plug on the picture tube will have a few
thousand volts on it even when the TV is turned-off and unplugged, stored energy
within the picture tube itself. so watch that.""

Will this still be the case when the set has been disconnected from all power for 4/5 days?

How would I get around this live voltage problem?

Lets say I find a flyback transformer and manage to replace it, turn the set on and discover that the fault is not fixed and I need to check other components. Is there anyway to discharge the energy on the anode plug safely, or at least be aware it's still there or discharged?

""The component that is sparking is the flyback transformer, it is integral to the operation of the set, its basically what powers the tube, you will need to buy a replacement one, other than that there's not much you can do. ""

The TV is a DAEWOO Model GB2898ST
28inh Colour TV, 240V 50Hz 75W

Do you think I should I remove the flyback transformer (hopefully not killing myself) and see if there is a component number on it and go that route?

Obviously I will Google as much as possible, but was wondering if you had any helpful advice on sourcing parts.

Thanks for your help.

 

[shrtrnd]

The voltage stored in the picture-tube will still be there 4/5 days later.
I take a needle-nose plier (with insulated handles), and squeeze the anode plug
attached to the picture tube (it's under the rubber cover), to release the metal clip
so that you can detach the clip from the picture tube. Then you can do what you
want with the flyback, which will have no voltage itself.
As Green Giant explained, it's good practice to just short the big electrolytic capacitors
with a screwdriver (plastic, insulated handle), in case they have any stored energy in them.
Some circuits have bleeder resistors to discharge the caps, and some don't.
AGAIN, Do not do any of these things with the television plugged into a power source.
I hope you're doing this as a study, and not EXPECTING a fully functioning television
that will last for many more years. Don't mean to be a wet-blanket, but your television
could very well have other problems that need to be repaired.

 

[ziggatron]

Thanks for the response, all points taken..

I will do as you say regarding detaching the anode plug from the actual tube, thanks for that.

Any advice on sourcing components beyond Google or any search techniques that might give positive results..

Thanks for your time and advice.

p.s email notification for this thread was automatically going to Yahoo.com's spam folder? For anyone else who does not get reply notifications, check the spam folder. thx.

 

[KrisBlueNZ]

To discharge the final anode voltage, I use a wire with a large alligator clip on one end (clipped to the braiding and springs that make contact with the aquadag, the graphite coating on most of the rear CRT surface), and a piece of metal at the other end that you can slip under the ultor cap (the rubbery cover at the end of the wire from the LOPT (line output transformer)).

Edit: LOPT is pronounced "LOPP-tee"; at least it is here in New Zealand.

If you make a wire for this, make sure the wire is thick and good quality, and make sure the connections at each end are visible. You don't want the wire to break without you knowing about it!

If you get a spark, leave the ultor shorted out for a while - say a minute, otherwise the ultor can "re-charge" because of the CRT's distributed capacitance. Then unclip the ultor cap from the CRT, and you should be safe.

I think you'll find that there will be no voltage on the ultor, because of the failure of the LOPT, but it's better safe than sorry.

Re discharging capacitors. The capacitors you'll find in a TV set don't really fall into the category of causing solder and copper to become projectiles, but they could take a small bite out of your screwdriver. I think your idea of using an incandescent lamp is a very good one. The highest voltage you're likely to see is around 350V which could concievably blow out the filament of a bulb I suppose, so you might want to check large capacitors with a multimeter after discharging them.

(There are capacitors that carry more than 350V when the set is operating, but these are low-value capacitors and they have a discharge path, so they won't hold a charge for more than a few seconds after power-off.)

As to whether it's worth replacing the LOPT, that depends how much a replacement would cost (if you can even source one), and how much the TV is worth to you. I think it's reasonably likely that there will be nothing else wrong with the set if you replace it, but obviously you can never be sure. Also consider the age of the set and how much longer the rest of it is likely to last. On the other hand, LOPTs are a common cause of failure, so by replacing it you may be extending its lifespan.

 

[ziggatron]

Hi,

Thanks again for all your advice.

@KrisBlueNZ

Thanks for your response mate. Because of the dangerous nature of removing this flyback I decided to do some more research, reading and videos etc.. must admit I was a bit hesitant but with enough research I felt comfortable to move forward.

I went with your idea for discharging the final anode voltage using a crocodile clipped wire attached to an insulated screw driver and the other end to the grounded braid. (Pictured) I have seen enough you tube videos of people arcing the flyback transformers for fun and also some one actually using exactly the same method you described where he got a audible "click" as the anode discharged. I didn't get any click, but I'm not doing this for fun, just want to repair the TV if possible and BE SAFE.

I have removed the main circuit board now, cleaned it up and desoldered the flyback transformer from the board. (pictured)

You can see form the photograph clearly where the transformer was shorting across two pins, sort of melted and very black.

I have done some initial research on sourcing a replacement flyback and surprisingly there are a few around. I live here in London UK and the supplier I have found initially is i the states.

I wasn't sure of the exact component number until today so I was previously going on what looked similar and came from a Daewoo.

It seems that one type of flyback will fit a few different models.

The supplier in the states I found is here..

http://www.technotronic-dimensions.com/Products2a_z.html

Pretty cool site, now looking for anything similar in the UK?

Fitting an identical part is well within my ability, but failing this, is it possible to source and use a generic flyback as a replacement? There are loads on Ebay for example and reasonably cheap.

I have checked the rest of the main circuit board over for obvious damage and apart from some mild discoloration in a few places which I would put down to prolonged heat it seems on the face of it in good condition.

Thanks for the help.

Edit::

I have found two suppliers straight away..

http://www.electrical-spares.co.uk/index.php?item=562

http://www.dalbani.co.uk/catalogue/product_details.php?id=7575

I notice one of them gives this warning about matching the item?

"" ALL DIGITS MUST MATCH - type within the message box (in the secure area, while purchasing it) all digits of the old LOPT so we can double check it before is dispatched
We cannot check for model compatibility, unless specified
THIS ITEM SHOULD BE FITTED BY A QUALIFIED ENGINEER

Image is only for display purposes ""

Any advice on this please?

You can see the label on my damaged flyback (pic'd), has these identification numbers..

1352.5008
50H0000181
4 49 99

4936 (in a traingle) :2

Any idea what all these refer to and which are the important ones in terms of sourcing exact replacement?

I searched using 1352.5008 and 50H0000181.

Thanks for your help.

 

[KrisBlueNZ]

Nice work! It's good to see someone who has some initiative and makes sensible and safe choices.

If that arcing is just on the surface of the LOPT - perhaps caused by dust and dampness on the top surface of the circuit board - you may be able to clean it up and apply some silicone sealant and put it back together. You need to remove every trace of discoloration. You may need to grind out some of the potting sealant using a dremel or similar.

If the arcing started inside the LOPT and bubbled out, there's no way to save it. In either case, clean the top of the circuit board thoroughly - isopropyl alcohol is best but any solvent will work.

Re using a generic LOPT from eBay, I wouldn't recommend it, but you might get lucky I suppose. LOPTs are custom-designed and have multiple windings on them, which all need to have the right characteristics. If it doesn't work, I doubt you'll be able to get any money back.

I have no idea which digits are important. If in doubt, as the website says, make sure that ALL digits match. I would go with the supplier who asks for the complete original part number. Also tell them the make and model, serial number, screen size, and year of manufacture, and any model or chassis number and revision number or date marked on the PCB. If they sell you a LOPT based on all that information, they're making a commitment that the part they sell is suitable; if it doesn't work, they might take it back.

Do a basic continuity check before you install the new LOPT. Use a multimeter on ohms or continuity range, and find out which combinations of pins have continuity between them, then confirm it's the same on the replacement.

Good luck! I hope it works out for you!

 

[Sinewave]

Very good thread.

Personally I'm petrified of touching flyback transformers. My Philips 32PW9586 has a flyback transformer issue, so even if I could get a new one, don't know if I'd be confident working with it. I'm fine and confident with working with electronics and electricity in general, but flybacks with that stored voltage in the tube just worries me.