Tv repair question

[techrex74]

OK, so I traced out the "no blue" tv problem to 2 open bias resistors at the color drive transistor. But now, the blue is way strong. Any advice on how to properly adjust the convergence without guessing, special tape to use or?

 

[Nigel Goodwin]

Well it's not 'convergence', it's 'greyscale' - but if nothing has been 'twiddled' then you shouldn't need to adjust anything - make 100% sure (and then check AGAIN!) that you've used the correct value resistors - they are usually 1% or 2% and difficult to read. It would also be EXTREMELY unlikely (I've never seen or heard of it) that two resistors on a single colour would be faulty. You've got two other working colours, compare them to the blue channel.

Usually it's the feedback resistors that go high, and you should replace all three!.

 

[zevon8]

Maybe there is a reason the 2 resistors were open circuit? Perhaps the driver transistor is faulty?

 

[Nigel Goodwin]

Maybe there is a reason the 2 resistors were open circuit? Perhaps the driver transistor is faulty?

That's why I queried two resistors faulty, ONE is extremely common, it's a high value feedback resistor (which values commonly go high or O/C) and it's also usually under-rated, I always replace them with 1W metal film resistors, basically as much for their voltage rating as their wattage.

 

[techrex74]

Nigel, thanks for the info. I too have never seen both resistor open Beyond 2M when color bands indicate 120K 2% (tested out of circit), and frankly it's been 10 years since I have even worked on a TV. Yes I did twiddle. But the set had zero volts at the blue drive pot. R and G had about 5V. Once I changed out the resistors, Boom, blue now present. Now that you said the replacements need to be exact, I'll change them out to the exact as I did not have, and used "close to". And yes I checked the color drive transistors (both OK). I have run the set for 24 hours now, still working.

 

[sheldonstv]

is it bright blue with flyback?check between the blue cathode and either heater connection........you may have a cathode heater short

 

[Nigel Goodwin]

is it bright blue with flyback?check between the blue cathode and either heater connection........you may have a cathode heater short

You've not read the full thread!

The original complaint was NO BLUE, with too much blue after changing the resistors (possibly for the wrong values?).

 

[things]

why are people trying to fix CRT's?? you can pick one up for dirt cheap now, or even an LCD one? if you still have too much blue, you must either have the wrong value resistor, or something else is playing up?

 

[gregmcc]

For me its still worth trying to repair them - if the problem is simple enough and is not going to require days of time. Its still a lot cheaper here to repair them than to buy a new one. And for a decent LCD its still waaaay too expensive, at least here in SA anyway.

 

[techrex74]

Hey all, thanks loads for all the help. I found this 25 in. stereo TV in the trash and thought I'd give it a shot, (recovering alcoholic needs to do somethingwith his time). I changed out the 2 bias resistors on the blue drive on the PCB on the tube, adjusted the gray scale and have had it running for 3 days straight, the unit is beautiful so far, made a great addition to my bedroom. Again, thanks to all the great techs out there.

 

[Nigel Goodwin]

You've never mentioned what set it is?, what make and model is it?.