Looking for help, CRT TV, color issue , trinitron kv-21r1d

[someguy7593]

Hey everyone.
I got this CRT TV from dead relative and I am hoping to fix it.

To not talk too much, I made a blog where I documented all the stuff, model, schematics,issue,what I tried so far, etc.
I am hoping to try everything in my power to fix it, but if the tube is damaged, I guess I will either scrap the parts or put it back and leave it as a kind memory.

If you have time, please take a look and tell me what you think, hopefully guide me to what should I test out next.

https://hmrkv21r1d.weebly.com/

 

[betwixt]

The problem is either lack of green drive signal from the video amplifier or the CRT green gun has lost emission.

You really need to use an oscilloscope to look at the CRT drive waveforms, with the color bars shown, the signals to the red, green and blue (KR, KB and KB) should be roughly the same amplitude. If green is low you have a fault in the video output stage, if they are about the same it's the CRT I'm afraid.

Beware of VERY high voltages on the CRT and connector board!

Brian.

 

[someguy7593]

Thanks Brian, sadly I dont have an oscilloscope, could there be some other tests I could do instead ?

Here's some thing I did in the mean time

Things I tried so far​

C board aka neck board :
-switched q702 and q703 to see if that makes a difference, NO FIX
-switched R721 with R722, NO FIX
-checked R709 and R710, in circuit they give 189 ohms, but out of circuit both 220 ohms, so they are good, NO FIX
-switched c705 and c706, NO FIX
-switched and checked Q708 and Q707,both good, NO FIX
-checked r718 and r717, both good 3.3k ohms value, NO FIX
-checked r745 and r744, both good 2.2k ohms, NO FIX

Voltage test CNC71 6p :
B in 6 = 3.15v
G in 5 =3.39v
R in 4 = 3.19v
IFB 3 =1.75v
+5v = 5.5v

Voltage test CNC72 5p
1 - +190v = 210v
2 - n/c = 0v
3 - E = earth 0v
4 - n/c - 0v
5 - H2 = 2.8v


Looking at PICTORIAL board these are all writings on it
(KB) B - 126v
(KG) G - 113v
(KR) R - 126v
EY4 - 60v
EY2 - 2.52v
Rest of the points give no voltage reading.
All were measured between the point and ground, of course, goes without saying.

I attached 1_orig photo which shows the issue and how it looks like on my TV
And rest of the photos are schematics.

 

[betwixt]

There is a trick you can try: At the CRT base, lift one end of R718 and R719, then temporarily cross link them to each others connections. This makes R718 go to KR instead of KG and makes R719 go to KG instead of KR.

The colors WILL be wrong but what matters is whether the green bar is now bright and the red bar is dimmer. If the green is now bright, the CRT is good and we can look at the electronics, if it is still dim the CRT is bad and there isn't much point in continuing. Let me know what you see.

Brian.

 

[someguy7593]

First the original

And then after doing what you said, crossing the resistors gets me this

So what am I looking at ? Its the tube worn out ? As in, its dead, can't be repaired unless tube is replaced ?

 

[betwixt]

Certainly looks like the CRT green gun has failed. Effectively what you did was swap the drive signals to the CRT over but it still has little or no green in it. The common factor is the CRT itself I'm afraid. If it had been a driver fault, the picture would be lacking red instead of green.

Brian.

 

[someguy7593]

I see, its OK, I am happy I tried and also learned a lot.Thank you Brian cheers