Sony KV-M1411U Video display issues

[Dagare]

Audio and controls for this TV seem to work perfectly fine, at first it seems to have no display what so ever, but turning up the scan shows a blue screen instead of white, and the OSD shows very faintly. The screen seems to change between 240p and 480i correctly with the input. I haven't been able to find any faulty components and all voltage readings I've taken have been fine. Has anyone run into this sort of issue before?

[Electronic M]

My HD-CRT Sony intermittently does the same thing with the red gun then goes into shutdown if I don't catch it in time. I've been trying to fix the issue for a few years. It was mostly a summer issue and I thought it was a CRT H-K short (tapping on the neck of the CRT would clear the issue for a while) and I actually floated the CRT heater supply to try and stop it (which worked for a few weeks).
This winter I became convinced it is a neck board IC issue... Humidity in the house drops well below %20 in winter and the issue always almost completely vanished in winter, and it did until mid winter this year when I got a humidifier and at %45 humidity the issue became as bad in winter as in summer.
I got a used neck board for my set and when I get time I plan to swap boards and see if that cures the issue.

[zeno]

Try this
Put blue drive back where it was.
Turn color level all the way down.
Put a source on it, composite easiest if it has it.
Measure these CRT voltages at the socket then report back
Use a meter safe to 1 KV DC This usually narrows things down.

R- K
B- K
G- K
G-2

[Alex KL-1]

In fact, several modern TV's and monitors especially ones having "cathode kine bias" DC current feedback from video output, for stabilyzing white levels, can shutdown the image if cathode currents are outside some preset values. Can occurs with shorted guns or weak guns.

[Dagare]

Originally Posted by zeno

Try this
Put blue drive back where it was.
Turn color level all the way down.
Put a source on it, composite easiest if it has it.
Measure these CRT voltages at the socket then report back
Use a meter safe to 1 KV DC This usually narrows things down.

R- K
B- K
G- K
G-2

Does G2 reach this high? I only have a meter rated to 600v so I may have to wait on this if it does.

[Alex KL-1]

Originally Posted by Dagare

Does G2 reach this high? I only have a meter rated to 600v so I may have to wait on this if it does.

Yes, is possible. Some CRT have "hot" G2. Is good to be safe/sure.
Some time ago I also had only a 600V Fluke DMM, and I needed to measure +Boost on a TV (near 900V). I carefully ajusted a attenuator asing the 600V range (on manual range) using lower voltage and a relatively robust potentiometer. then, I sub it with a array of series 1kV rated resistors to achieve correct value, and measured perfectly on the 600V range (in that time, I only made a 2:1 att; eg. 900V reads 450V).
Nowadays I restored a tube MM, using HV resistor on voltage scale divider. Resulted limited only by switch, and I comfortably use it's own full 2kV scale without any trouble.

[Dagare]

Originally Posted by Alex KL-1

Yes, is possible. Some CRT have "hot" G2. Is good to be safe/sure.
Some time ago I also had only a 600V Fluke DMM, and I needed to measure +Boost on a TV (near 900V). I carefully ajusted a attenuator asing the 600V range (on manual range) using lower voltage and a relatively robust potentiometer. then, I sub it with a array of series 1kV rated resistors to achieve correct value, and measured perfectly on the 600V range (in that time, I only made a 2:1 att; eg. 900V reads 450V).
Nowadays I restored a tube MM, using HV resistor on voltage scale divider. Resulted limited only by switch, and I comfortably use it's own full 2kV scale without any trouble.

Thanks for the explanation. My knowledge is patchy so I will wait until I can get a higher rated MM instead of improvising.

[Electronic M]

Originally Posted by Alex KL-1

Yes, is possible. Some CRT have "hot" G2. Is good to be safe/sure.
Some time ago I also had only a 600V Fluke DMM, and I needed to measure +Boost on a TV (near 900V). I carefully ajusted a attenuator asing the 600V range (on manual range) using lower voltage and a relatively robust potentiometer. then, I sub it with a array of series 1kV rated resistors to achieve correct value, and measured perfectly on the 600V range (in that time, I only made a 2:1 att; eg. 900V reads 450V).
Nowadays I restored a tube MM, using HV resistor on voltage scale divider. Resulted limited only by switch, and I comfortably use it's own full 2kV scale without any trouble.

There's another way to measure 1KV on a 600V meter. Find a 400V B+ source measure it with respect to ground and record the number, then measure the 1KV point with respect to the 400V B+ then add that value to your recorded value to get the actual value of the 1KV source....I did this once on an early SS RCA I was fixing on site with limited tools at a friend's house. It worked great. I think in my case it was a 900V boost, a 350V B+ and a 600V meter, but the same principle applies if the TV has power supply rails that are a good fraction of boost.

[zeno]

Most G-2 run off a divider. First the focus apx 6KV is dropped by high
ohm resistors off the HV. then the low side of the focus is divided out
to put the G-2 in range. Typ G-2 is 400 +- vdc.

Alex mentioned A.K.B. ( auto kine bias) & yes most Sony used it.
They also made it so the video would be cut off if the jug was weak.
I asked Sony FS tech about that & he said sony did NOT want a set with a bad pix so you get none !
Symptom usually no raster then blinking raster as it warms up.
On AKB sets if you shrink the V size a little you will see 3 color stripes
at the top. Thats the guns firing to collect current data.
A few more tricks if need be.

Anyhows I am going to cool off. Spent the morn at Hampton beach N.H.
and wow was it hot

Zeno

[Dagare]

Sorry for the delay, been pretty busy.

These are the reading with composite input, these seem in good range but I'm not 100%.

kg 193.6
kb 202.8
kr 202.8
g2 535.0

[zeno]

Originally Posted by Dagare

Sorry for the delay, been pretty busy.

These are the reading with composite input, these seem in good range but I'm not 100%.

kg 193.6
kb 202.8
kr 202.8
g2 535.0

Seems to be no video at all. G-2 OK.
Cathodes are at VCC voltage so no raster. Now it depends on where the video comes in. Usually its to the RGB outputs emiters. Sometimes in the
jungle IC.
With AKB you can look at the CRT condition. Each output & K is fed by
about a 27K 2 W Ground the collector with a same value resistor. ,
one C at a time. Should get nice brite color for that gun.
Mucky dim color is usually the CRT.
& remember the lower the K voltage the briter the pix.

Zeno

[Dagare]

Thanks for the response Zeno.
So if I've understood everything correctly, there are at least two issues.
Video input is dead, but osd + top rgb lines are there, so the issue has to be between the jungle ic and input, as its a direct line to the neckboard from jungle and osd shares rgb input from what I can see on the schematic.
Then either the tube is worn or there is an issue on the neckboard.
With g2 set correctly but reducing vertical size, the blue line shows fine, but red and green only show after boosting g2.
If I disconnect the vid input cable from the neckboard, the screen is still blue when boosting g2.
Do I need to input a white screen to check the tubes health?

[zeno]

I would feed it so it gets sync. Some sets blank or go blue
without H sync. And remember it tests one gun at a time.

If you are SURE its the CRT try this. There is a low ohm resistor
usually 1 or 2 ohms 1 or 2 watts in series with the filament. You
can jump it out & get more time out of it. There is some RISK doing
that !

Zeno

[Alex KL-1]

I wonder about the screen being too blue... most CRT react to high Vg2 displaying gray/white or faintly coloured... I fear that the red/green being weak.
So is interesting to follow the zeno suggestion to check it.

[Dagare]

Ok so I was able to rule out the tube as the issue, its actually in very good shape.
Luckily I have a working kv-14m1a laying around which uses the exact same tube + yoke that I could test it in.
Guess that issue must be on the neckboard, back to testing.