Worn CRT or other issue? (Sony)
 

I recently picked up a Sony KV-20V50 mfg in 1993. The picture had a red bias/tint/whatever you want to call it. I messed with the gain/cutoffs in the service menu and got it to look a little better. The overall image is still fairly sharp, but there's a bit of horizontal smearing.

I went over the power supply board and main board with an ESR meter and found several caps with high ESR. I replaced those, and the image cleaned up a little, but I still can't get the colors dialed in properly. There's also a pulsating blue horizontal line that shows up at the very top of the screen when the TV is first turned on, and it goes away after a while.

Also, I noticed that the screen control (which is on the neckboard and not the flyback) doesn't seem to have a large range. It either goes super bright with retrace, to bright, to completely blanking the picture.

Just for fun, I measured the cathodes and the red cathode was always at least 10-20v higher than green and blue. I'm not sure if this is normal as I'm still learning all this stuff.

TLDR: What are some ways to determine if the picture tube itself is on the way out, vs some other problem?

I had a similar tracking issue in a KV-20FV12, caused by a soft CRT. The cure would be to raise the CRT heater voltage a bit. Not being a Sony specialist, I didn't know if there's a resistor in series with the CRT heaters (as there is in many brands). It would be a small value, like 2 - 3 ohms, and would be on the neck board. So I asked the Sony gurus on here, and sure enough there is. So I jumpered that resistor an lo, the Jug came right up and looks great to this day. If yours has that resistor, try jumping it temporarily and see if the tracking improves.

1) on the CRT board there are 3 identical 2W resistors. They feed the
R,G & B outputs. Where they join is apx 200VDC. Follow that line & you
will come to a cap typ 4.7 mfd 350 volts. change it.
2) check resistors off the G-2 control. High ohm values & they like to
open.
3) blue line at top is probably the AKB ( automatic kine bias) firing.
With AKB each gun is fired & measured during retrace & automaticly
adjusts the grey scale. Normaly on a Sony with AKB & a weak CRT
the video will blink on & off but less as the set warms.
4) keep in mind the cathode voltages will all be a little different.
The lower the voltage the higher the brightness of that color.

73 Zeno:smoke:
LFOD !

I assume it's R704 in this picture? You mean you removed the resistor and jumped the two points with a wire? I might try that.



Thanks for the info as always! I forgot to mention that I replaced all of the resistors around the G2, as I had read somewhere else that those can go bad. I didn't find any caps with the value of 4.7uf 350v. According to the service manual, the highest value cap with 4.7uf is c523 4.7uf 160v. I think I changed that one already but I'd have to go back and look.

Here's the service manual if anyone is interested.

https://drive.google.com/file/d/19P2...ew?usp=sharing

Yep, that's the one. I left the resistor in place and jumpered it with a wire.

follow the 200 v line down to the main PCB. It should be near
the FBT. Its a common problem on all brands.

That's an excellent model, Sony's best 20" from the era. Good luck with it.

quick update: Finally added RGB to this TV like I'd planned for a while. It was dead simple, just injected into the CC daughterboard header.

Looks WAY better than even s-video. Very crisp image.

There's still a red bias to the gray scale. I stuck a colorimeter on it and it confirmed it for me. There's no red cut or red gain in the service menu so I wasn't able to dial it down. Any suggestions? Is the red gun working harder to compensate for the other guns? Also, I seem to recall reading a specific reason why sony CRTs don't have red cut/gain available to adjust but I can't quite remember.

If it's favoring the reds, then the green and blue aren't doing their jobs, which is pretty typical for a TV like this with a bunch of hours on it.

If the CRT is strong, you don't need those other adjustments. I would guess it was a cost decision.

When you're dealing with an unbalanced tube, the more adjustments you have the better. One manufacturer (can't recall now) had low, mid, and high drives for all three guns in the service menu.

John

Thats what I was afraid of. Well, I'll just enjoy this TV while it lasts and keep an eye out for possible tube swap candidates, but 20" Sonys are becoming quite rare around here.

If the red is stronger than the other primaries and you don't have controls to turn red down, why don't you just increase green and blue to balance the grayscale?

I tried. No matter what I did, I couldn't get the grayscale balanced very well at all. According to my colorimeter, using HCFR, the red was over 150% and I couldn't get it to go down much, if at all. Also, the drive/cut controls didn't seem to have a very big range.

Do this. Measure the 3 cathodes (K) of the CRT at the socket & post them.
Should be abt the range of 125-150 VDC.
With AKB the way Sony did it things dont make sense. If its the CRT
you should get the pix blinking on & off especially when COLD.
A dominant red may indicate a problem in the red BUT usually would come
with thin white lines in the pix. If you can post a pix with the color
level all the way DOWN it would help.

73 Zeno:smoke:
LFOD !

R - 134.4v
G - 128v
B - 127.5v

Here's a pic with the color set to 0. That moire in the middle is just from the camera.
https://i.imgur.com/8wgYpAr.jpg

I've only had this TV a few months but the picture has been rock solid, no blinking at all. I mentioned in my original post that I could see a horizontal blue line at the top that would go away after a while. Today, when I turned it on, I could see the R and G line too, along with the blue line, but they all disappeared after the TV was on for a few min.

OK the voltages look with in reason. So you may have
1) a very slightly weak CRT
2) something very slightly off in the red or the jungle IC.
The pix looks very good otherwise. You may want to check
all the resistors in the red from the jungle IC to the CRT.
Be sure to lift one end to check. Beyond that you could go
up in value on the red out collector resistor ( typ 18 K 2W ) a little but
leaving it alone may be the best....

73 Zeno:smoke:
LFOD !