Looking for help to repair CRT TV, bad colors

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randod2236

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Hey guys. could anyone help me out with finding out what is wrong with my Sony Trinitron CRT TV ?
To not clutter the post too much, I made a website with all the the details

https://hmrkv21r1d.weebly.com/

I showed what the issue is, what I tried so far and voltages that I tested.
I also have the schematics there as well.


How it looks like on the screen




(here are schematics from service manual​

​

​

Block diagram​

View attachment neckboard.jpg < Neck board
View attachment bigmainboard.jpg < Big main board

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
(Bold) is how it is written in schematic board view
(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.
 
Last edited:
randod2236 said:
To not clutter the post too much, I made a website with all the the details
Click to expand...
Not the way to do it. Posts here should be complete and ALL on this site. The reason for this is that it becomes a reference for the future. Someone may google your question in 5 years time when your site has expired and won't find the answer.

Mike.
 
Red, Green, Blue are the Primary colours in a colour TV.
From your test pattern it looks like the Green is not lit. Check your Green gun drive.
 
You haven't done the basics - the first thing you do in such a case is run your meter round the CRT cathodes (marked KR, KB and KG) - the lower the voltage the brighter the colour - if green is appreciably lower than the others (as I suspect) then the CRT is low emission.

As a crude (and very) nasty extra test if above shows the CRT is at fault, I would then stick the meter on ten amps range (essentially a S/C) and 'blip' the probe very briefly across each cathode in turn. You should get an excessively bright screen of each colour as you do this, and if one colour is faulty that will be no where near as bright as the others.

But from your pictures, it looks like CRT to me - as you would expect on an antique set.
 
Pommie I added details here now, what you said makes sense, thanks.

Ramussons I am not sure if I know what do I check here and how, could you elaborate ?

Nigel Goodwin , I really have no knowledge on CRTs, that will help, thanks.

Looking at PICTORIAL board these are all writings on it
(Bold) is how it is written in schematic board view
(KB) B - 126v
(KG) G - 113v
(KR) R - 126v
EY4 - 60v
EY2 - 2.52v
Rest of the points give no voltage reading.

Just to be sure I did it correctly as I have no knowledge about this , I'll write in detail
So I just did what you said about 10 amp blip test, I set multimeter to 10 amps, put the probe in 10 amp socket, connected black com probe to the ground and then touched KB , KG and KR with red probe for 1 second, blue is good, but green and red seem to be weak.

What does this tell me ?

And btw quick question, while doing these tests, does the TV have to be showing anything, like should I switch to some channel or connect a console to it, or is it enough to just turn the TV on and leave it on a blank screen ?
(this TV when turned on(not the standby), does not show static when I switch to empty screen, it just shows black screen instead)
 
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It shows the CRT is low emission - not unexpected on a set of this age.

It would have been my first guess without doing any tests at all.
 
Do you have a scope?
You measured at "R, G, B" at the tube. I wish I could see the ac voltage at "G" as compared to "B". There is a chance the Green video amplifier is bad.
If we had a more detailed schematic, we could adjust the Green to see what is happening.
 
ronsimpson said:
Do you have a scope?
You measured at "R, G, B" at the tube. I wish I could see the ac voltage at "G" as compared to "B". There is a chance the Green video amplifier is bad.
Click to expand...

No chance at all, my 'blip' test (although I wouldn't really consider a second on each cathode a 'blip') bypasses everything external to the CRT. The CRT is worn out, as simple as that, it can't be the amplifiers.

ronsimpson said:
If we had a more detailed schematic, we could adjust the Green to see what is happening.
Click to expand...
He posted the full circuit above.
 
Yea I am probably going to scrap the boards for parts, since its safe to say its no repair if CRT needs to be replaced.

Thanks guys.
 
Nigel Goodwin said:
No chance at all
Click to expand...
You have more experience on old used TVs. You are most likely right.

I made prototypes of Sony and the tubes were usually good. The video amps were not. It was common to find a broken bias pot or a dead transistor from "sparks". I just wanted to adjust "black level" for green to see if there was anything left of the gun.
 
Trinitron CRT failure was common, and 'blipping' the cathodes instantly eliminates everything else other than the CRT.

It would be 'nicer' to use a resistor to pull the cathodes low - but you generally don't have a large resistor with wires on handy at the time, but the crude meter method works fine (and is probably already connected as you've been measuring the cathode voltages).
 
Nigel Goodwin said:
It shows the CRT is low emission - not unexpected on a set of this age.

It would have been my first guess without doing any tests at all.
Click to expand...

The colour test pattern should show a Red, Green and a Blue Band beside other colours. The Green is missing in your test pattern display.
Try this. Interchange the Red and Green (pin 9 and 10) and see if you get a Green Band on the test pattern. If you get a good Green band, the problem is in the Green colour electronics. If you still don't get a Green band, the tube is faulty.
 
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