Since i am not television repair person i just a hobbyist interested in electronics,I will patch the crack in high voltage wire where spark jump with silicone And after patching the wire and if a new area of the wire start spark that mean maybe got problem with high voltage.
mrel

Failure to verify the EHT level is inadvisable!

Continued operation at excessive EHT levels will not, necessarily, result in further failure of anode lead insulation (hence said failure must not be regarded as diagnostic/exculpatory of same) but will certainly stress, degrade and/or destroy the LOPT and other components -- moreover, there are distinct fire and (long term) X-ray exposure liabilities...

EHT probes are inexpensive and readily available.

Here is an example of an inexpensive, high quality, self contained (DC) EHT voltmeter:
http://www.mouser.com/ProductDetail/BK-Precision/HV-44A/?qs=OfNnNsH3l7sGI0%2bK50GGug==

Best regards
HP

 

In that case the problem is indeed a faulty anode lead and, possibly, excessive EHT...

Excessive EHT was common with the old hybrid CTVs, and usually hinted at a clapped out CRT not drawing enough current - most solid state sets I encountered had some form of X-ray protection that usually sensed excessive EHT. The early ones shut down the contrast and brightness to protect the CRT, but pretty much anything with a front panel micro would shut down to standby.

One fault that can fool the X-ray protection, is the horizontal flyback tuning capacitor - most manufacturers use a self healing capacitor that doesn't arc and burn, it just chimbles away the foil and gradually reduces in capacitance - the symptoms are reduced width with excessive EHT.

 

Failure to verify the EHT level is inadvisable!

Continued operation at excessive EHT levels will not, necessarily, result in further failure of anode lead insulation (hence said failure must not be regarded as diagnostic/exculpatory of same) but will certainly stress, degrade and/or destroy the LOPT and other components -- moreover, there are distinct fire and (long term) X-ray exposure liabilities...

EHT probes are inexpensive and readily available.

Here is an example of an inexpensive, high quality, self contained (DC) EHT voltmeter:

In most cases; if the B+ to the horizontal output stage is correct, the EHT will be too - but see my post which mentions the flyback tuning capacitor.

 

the symptoms are reduced width with excessive EHT.

Ah yes! Increased EHT sans (significantly) increased horizontal deflection current -- shades of ye olde 'shunt regulated' schemes (via the 6BK4/6EN4 and their ilk)...

the horizontal flyback tuning capacitor - most manufacturers use a self healing capacitor that doesn't arc and burn

I recall ceramic tubular caps conspicuously marked "SPECIAL" --- always wondered what the deal was, now I know! Thanks!

In most cases; if the B+ to the horizontal output stage is correct, the EHT will be too

Just so -- Still, IMO, verification of EHT magnitude should be regarded as essential following repair of associated circuits -- While it is my considered opinion that the X-ray 'hazard' (such that it is) is overstated to the point of hype and/or hysteria -- the fire risk attendant to continued operation at excessive EHT levels is indisputable! At ~ $100 (USD) for an accurate self contained EHT VM there is no excuse for laxity in this regard -- My $.02

Best regards
HP

 

TWEEET! (That's a whistle.) Referee here: I see one person repeatedly saying, "Do it the correct and safe way." and the other person repeatedly saying, "I choose not to, and offer these excuses for my frugality and laziness." Please agree to disagree or I'll show each of you a yellow card .

That said, I think $120 plus shipping for a meter that only does one job is, "expensive" compared to its utility. The last one I had crumbled at the tip and thus committed suicide. I can offer the idea that x-ray fears only started causing compensation techniques when the voltage levels approached 32KV. I would not fear a 20KV CRT. Besides, difficulty with the focus adjustment is going to reveal the problem, if there is one.

 

Ah yes! Increased EHT sans (significantly) increased horizontal deflection current -- shades of ye olde 'shunt regulated' schemes (via the 6BK4/6EN4 and their ilk)...



I recall ceramic tubular caps conspicuously marked "SPECIAL" --- always wondered what the deal was, now I know! Thanks!
HP

The usual thing is reduced capacitance upsets the resonance of the predominantly inductive flyback system, more energy appears at the flyback pulse voltage, and less energy is available in the scan current department.

A slightly different scenario was common in the early days when they couldn't make high enough voltage horizontal transistors, what they did was stack 2 horizontal transistors, each with its own tuning capacitor and secondary on the horizontal driver transformer. The base of each transistor was fed via a reactance winding, the 2 inductors shared a former and tuning slug that moved between them for drive balancing.

If one of the capacitors reduced in value, the peak voltage would increase and the associated transistor would eventually fail short circuit. Since the normal situation has 2 capacitors in series, the shorted transistor makes that just one - and the capacitance is then double the required value. You'd end up with the picture stretched way off the sides of the screen.

 

...difficulty with the focus adjustment is going to reveal the problem, if there is one.

Well... I feel symptom based diagnosis (while of definite utility) is recklessly relied upon in safety-critical situations --- Moreover, what's $120 (USD) in this day and age? Seems little enough for the peace of mind alone...

That said, I wholeheartedly concur with the notion that the consumer-product X-ray 'hazard' is greatly overstated! -- 'Physical insults' requiring decades to allegedly produce frank illness are 'easy prey' indeed for avaricious barristers -- where the merest dubiety as regards etiology is seen to exist

Very Best Regards
HP

 

May I suggest, Google, "DIY KV probe".

 

May I suggest, Google, "DIY KV probe".

Good idea -- The divider resistor{s} can be tough to source, though...

 

Good idea -- The divider resistor{s} can be tough to source, though...

www.mouser.com

http://www.mouser.com/Passive-Compo...0vkovZ1z0vkogZ1yzu4rmZ1z0vkk4Z1z0z819Z1z0wljo

 

www.mouser.com

http://www.mouser.com/Passive-Compo...0vkovZ1z0vkogZ1yzu4rmZ1z0vkk4Z1z0z819Z1z0wljo

Should be ok so long as the resistor length ~ 5mm per kV of anticipated maximum EMF (Re: atmospheric insulation) -- should you find such resistor{s} difficult to source, you may, of course, 'series' several lower-value units in geometrically linear dress...

Best regards
HP

PS: For the life o' me I don't know why anyone would want to take on all this rigmarole when < $200 will place the required instrument in his/her hand???

But then, perhaps, I'm just lazy -- Its a fair cop...

 

Yes, that is the essence of the instructions for a DIY KV probe. Read the ratings for the resistors, place several in series. That results in a probe long enough to keep your fingers out of harms way.

 

That results in a probe long enough to keep your fingers out of harms way.

And to prevent flash-over with lamentable consequences to the connected DVM!

 

If the voltage had jump from 120 volt to 135 volts would this television put out more X-Ray?
If the voltage gone higher as in your post if putting silicone on the wire can stop the spark jump to the picture tube if voltage go higher than 135 volt which is high would that put more X-ray out?
mrel

yes the high voltage will be higher and there will be more xray emitted, if you have a high voltage probe you can check it easily. Mostly the sets have a protection circuit built in but that doesn't mean they are working correctly and shutting down the set. If you have a schematic look for high voltage protect or x-ray protect circuit.

 

May I suggest, Google, "DIY KV probe".

One of the magazines published an EHT probe in the last few years - might have been EPE. if it wasn't them it must've been Elektor.

 

The usual thing is reduced capacitance upsets the resonance of the predominantly inductive flyback system, more energy appears at the flyback pulse voltage, and less energy is available in the scan current department.

Emphasis added

Then too, of course, required deflection current is (non-linearly) proportional to accelerating potential (and, hence, effective electron velocity)...

 

Hello All
Is there a website where i can get free download of schematic for this television mention in this post.
looking for RCA television model 20f420T ,make by TTE Technolog inc.
Serial number H022E7BD6.
Need schematic to check high voltage circuit
mrel

 

Hello All
Is there a website where i can get free download of schematic for this television mention in this post.
looking for RCA television model 20f420T ,make by TTE Technolog inc.
Serial number H022E7BD6.
Need schematic to check high voltage circuit
mrel

For best results please try posting your request to the "Electronics Resources" forum of this site

 

For best results please try posting your request to the "Electronics Resources" forum of this site

Nobody likes a minimod, gf!

 

Nobody likes a minimod, gf!

Yikes! -- Actually that was not the intended tone of my post

PS --- Not being especially au fait with 'IM shorthand' - might I bother you for an expansion of "GF"?