White Balance Failure - Sony KD-34XBR970

[user181]

I have a Sony KD-34XBR970, which is a modern HD CRT set. A couple weeks ago while in use, the standby/timer LED began blinking a diagnostic test code. The code is 5 flashes of the LED, which the service manual states is "White Balance Failure." The set has continued to function with no observable degradation to the picture. The LED flashes the diagnostic code even when powered off, but unplugging the power cord resets this until the next time it is power on.

I have attached an excerpt from the service manual which defines the error code and lists probable causes. Does anyone have any experience with repairing this issue? Of the probable causes listed, is there one which has been the most common?

Do any of these repairs require extensive adjustments to complete? Since this set is such a complicated system, I'm trying to understand if there would be more effort involved than merely replacing ICs or swapping a board.

Lastly, given that the set is working right now, what is the typical progression of this fault?

[vol.2]

Interesting. Someone else here might have experience with these weird beasts, but they are extremely complicated inside.

My first impression is that the fault code itself could be the fault. I have fairly extensive experience troubleshooting automotive computers, and sensor fault is by far the most common outcome of things like ECU computers. I haven't ever seen the situation you are experiencing, but I would tend to think it's highly suggestive of a failed sense circuit that is incorrectly reporting a failure.

That being said, it would be most prudent to check and make sure that all specified conditions are okay.

ICs do fail sometimes, but most issues I've encountered are due to failed components that support the operation of the ICs. Leaky caps, drifted or cracked chip resistors, noisy or failed transistors, etc. And when the ICs fail, it's typically because of the failure of something else in the circuit.

Again, I'm not sure if someone else here has specific knowledge of Sony HDCRT failures, but I think it would be extremely difficult to speculate on the nature of a fault that doesn't seem to have occurred (at least yet).

The only path I would see open (to myself in the same situation) is to check the G2 and the areas around where the ICs are located that the service manual is complaining about. Sometimes you get lucky and there's a burned mark on the PCB, or a visibly damaged component.

[Electronic M]

I have had a couple of DA-4 chassis songs like that 34XS955 34XBR960, but I don't remember that 5 blink fault. The 955 had an interesting problem where it would randomly (sometimes first drift red) go completely red screen with retrace lines and shut down when it was somewhat humid...If you could give it a knock before shutdown it would fix it's self. Tried floating the heater (figured heater cathode short) and while that briefly reduced it it didn't fix it. Was going to swap the neck board but the 960 presented it's self cheap before I got around to it.

The service manual can be found free on the net and explains how to get into the service menu if you need to adjust grayscale. Write down all the values before you change anything as well as the resolution and modes you are in (some settings have multiple values and each different one will only display and adjust depending on resolution of signal or picture user preset mode.

A lot of these sets come from factory with excessive overscan. I've gotten good at fixing that in the service menus.

[zeno]

The set has AKB ( Auto Kine Bias). During blanking each gun is fired
and measured to adjust grey scale. Usually its the CRT. Symptoms
are slow warm up, blinking or no video. The pix may not be as good also.
For now I would leave well enuf alone. At most turn up the G-2 just a tad.

Zeno
LFOD !

[user181]

About a year ago, the set was having an issue with the image in which there was some horizontal smearing in the picture that was most noticeable when the picture had a dark colored area right next to a white or lighter colored area. The smearing looked reddish. It also had some faint horizontal streaks or lines in the picture. This had been going on for some time.

But then one day (about a year ago) while the set was on, there was a very quick 'zap' noise from the set. It was so quick I didn't even realize where it was coming from at first. My daughter was in the room and heard it too. From that point onward, the issues with picture were gone.

I've never been sure what the noise was, and have wondered if it was either a component that will eventually fail, or if dust/debris maybe created a partial short somewhere that cleared itself. But the picture was instantly improved.

The service manual mentions IC9001-9003 which are video output amplifiers for the 3 colors, so I'm wondering if those could be related to the issue from the past and the "white balance failure" error code now.

[zeno]

The old symptom you had sounds like the common bad cap
on the @200 volt supply. That feeds the 3 color outputs.

Post the schematic of the CRT PCB & that will help.
Almost all sets with that symptom are either that cap or the CRT,
thats sets of all brands ( hundreds of repairs ). It is probably in the
top ten of all problems from @1980 til the end of CRT sets.

Zeno

[user181]

As requested, I've attached the schematic for the CRT board (the "CH" board).

[zeno]

At CN9002 pin 1 just be sure there is 200 VDC.
Other than that I would leave it be.

Zeno

[vol.2]

Originally Posted by zeno

At CN9002 pin 1 just be sure there is 200 VDC.
Other than that I would leave it be.

Zeno

Maybe he should pull and check those 3 10uf 250V filtering caps on the video amps?

[user181]

I'm OK with leaving it be. The standby LED will blink the code ad-infinitum unless power is unplugged to reset it. Any issues with leaving that go long-term? This set is still the living-room TV.