Sony PVM-2730QM no HV

[Rotary]

Helle frineds of reparing electronic stuff :-)

My good old Sony PVM-2730QM seems to have some issues after a decent period of sleep.
When i powerd it up a few days ago, controlpanels and audio comes on, i hear the HV followed by the switch HV of sound after a second.
Meassuring a few voltages proofs this. All Voltages from the main power supply are present. the voltages from H drive are missing so I assume the HV protection circuit kicks in.
After a lot of measuring and turning the TV on and off via remote it suddenly stayed on for 5-10 seconds. A few meassurings and powercycles more it stayd on for arround 45 minutes now and still runing.
But near all voltages arround the protection circuit and HVR1 and HVR2 (HVRBUFFER IC1503) feddback are far away from teh datasheet and i cant locate the source of those over and under voltages.

Are anyone here familiar with this PVM and can help me out with some infos or ideas ?
Thank you very much.

[shakalnokturn]

No experience with this model, plenty of experience with other CRT TVs.

First of all beware of dust and dampness if you powered it shortly after bringing it in from a cold environment, it can be enough to cause HV related problems.

If there is a real fault unfortunately the most likely cause is going to be the HV transformer or HVR block because they are very stressed parts.

With the back cover removed are there any ozone smells, crackling, purple glow around the HV components when looking at it in the dark?

Anything unstable on the picture? Brightness, focus, geometry variations?

[Rotary]

Hey,
tanks for reply.

Ther is no abnormal glow or strange smell noticable. I had the TV running for gaming yesterday for 3 hours without shutdowns. It even turned on today without hickups.
This TV has a cascade after the flybacktransformer where the fedbacklines for protection circuit is coming from, too. This voltages are very low compared to the values in the schematics. But is it possible to deliver a clear picture with near a 1/4 of the usual voltage.
Interesting thing was, it first powered up while i was measuring the feedback voltage with my DMM. Next try without DMM it was shuting down. With DMM its started again.
With every try it stayed on for a bit longer.

Only thing i noticed on the picture,  the more white is displayed on screen ,the more the left side of teh picture is "bowed"? So its not a straight line its deformed a bit.
I will try to post a picture of that later.
Does this may be in context with a low HV ?

[shakalnokturn]

Usually low HV will result in a zoomed picture and less brightness.

If anything yours may be too high. I doubt it is normal to actually see the end of the scan and pincushion. (Does the pincushion adjustment work?)
Getting it to start while measuring feedback voltages at IC1503 would also point to excessive HV as the DMM's input impedance will have brought the voltages down.
Also beware of your readings, the resistor values in the HVR are obliously very high, the 10MΩ of your DMM are seriously going to influence what you're trying to measure. The sanity check should be on IC1503 outputs if anywhere.

(Looking at that schematic on my phone is wrecking my head...)

[andy2000]

While I have no experience with this specific model, I have seen Sonys where a bad HV feedback block caused weird shutdown issues.  You may need to get a HV probe so you can measure the HV directly. 

The HV regulation should be rock solid in models like this with direct HV feedback.  Most TVs just regulate the B+ and hope for the best, or use one of the lower voltage flyback secondaries as a reference. 

The fact that it works better after more use might point to bad capacitors.  This is more likely if it's a heavily used monitor, or was stored somewhere hot. 

[Runco990]

I have repaired THOUSANDS of Sony PVM and BVM monitors.  FIRST THING.... get out your ESR meter.  Number one failure are Capacitors.  Small value high voltage, i.e. 10uF 160v, etc.  They were dying 20 years ago already, so I'd bet you that's your problem.  Same with pincushion on that model.   

[Rotary]

Thanks for your thoughts.
Its not that long ago since i replaced the caps (electrolyte) on the D-Board when i had a blown Q510 VDrive transistor, but i will check again, maybe i missed one.

Anyway i took the following voltages.

IC1503

     my reading / value in schematics
1 = 29,4 V   /   26,8 V
2 = 1,4 V     /     9,6 V
3 = 1,4 V     /     9,6 V
4 = 1,0 V     /     9,5 V
5 = 0 V        /      0 V
6 = 1,2V      /    14,4 V
7 = 22,6 V   /    14,4 V
8 = 22,6 V   /    14,4 V
9 = 29,4 V   /    26,8 V

IC1502
1 = 10,8 V   /    10,9V
2 = 6,8 V     /    6,8 V
3 = 6,8 V     /    6,8 V
4 = 6,8 V     /    6,8 V
5 = 0 V        /    0 V
6 = 9,2 V     /    5,9 V
7 = 6,0 V     /    5,9 V
8 = 9 V        /    5,9 V
9 = 10,8 V   /    10,9 V

Q1520
C = 17,5 V   /    11 V
B = 4,2 V     /      1,8 V
E = 3,6 V     /      1,4 V

all while TV is on.

On the attached picture you can see the deformation a little bit