Sony KV27EXR20 comes on with sound 10 to 20 minutes before picture

The CRT is failing. The AKB circuit blanks the screen if the emission is below a certain point. You may be able to get a little more life out of it by increasing the G2 voltage a bit.

David

Thanks David! Is that an adjustment on the flyback?

Usually, yes (the lower one). Some Sony sets had the G2 adjustment on the CRT socket board. I do not recall which one was on this model.

David

That's certainly possible, but before condemning the CRT it's worth making sure that's the problem. When I've seen this happen, the picture will flash for a while and then finally come on, if it didn't do the flashing thing, suspect something else.

Just what the other guy said, weak CRT causing the AKB circuit to blank the picture.

I found the G2 on the board attached to the CRT. When I dial it up the flickering begins sooner than before. It certainly isn't acceptable. I saw a post from 1999 from a David which may have been you.

"Here is a bit of information regarding the video blanking at turn on in Sony tv sets that use the IK detect line.

With the tv set in a full cold start, look at the cathodes of all three of the guns with the oscilloscope. It will take some work with the scope settings to see the blanking pulses during the vertical retrace time.

Take a good look at the pulses, they all 3 should be fairly close to the same P-P value, usually between 50 and 150 volts. If one of them is much smaller or much larger than the other 2 the crt guns are getting very weak and way out of balance causing the blanking problem at turn on. At this point the only proper fix is to replace the picture tube.

In about 50% of the cases a newer low current crt rejuve only on the bad gun can sometimes rebalance the guns for better AKB performance. In some other cases a slight increase in the g2 voltage will allow a better turn on and gray scale.

We have seen a lot of older Sony tv sets coming in with the same symptom as he described it with the above troubleshooting and failure result.

Some older sets also had bad solder connections to all of the voltage regulators in the center of the main circuit board.

The ones with the stand up power supply on the side of the chassis have a special capacitor 1000uf16v that goes bad and can cause poor power supply regulation.

David".

I hate to toss out what was a very nice set. Do you have any thought that the power supply board could be at fault? I could certainly replace the capacitor mentioned above if it would do any good. I apologize, I'm still in denial.

Barry

You could measure the output of the power supply, but the tube is almost certainly shot. Perhaps you could find a lightning damaged or otherwise defective set with a good tube? If you're in the Seattle area I have a dead

how old it this tv?

-B

weak. It is possible to have a power supply fault that can cause this type of symptom, but that is very rare. When the CRT is very week, the AKG circuits keep it biased off. In the case that the CRT is taking very long to warm up to have enough emission, the AKG circuits will keep it biased off until the emission is high enough.

At this point, I would be looking for a new TV set.

Jerry G. ======

Hello Berry,

I did not write the archived post, but it appears largely accurate.

I assume you do not have a schematic of this set, but there is one more thing you can try. You may have low heater voltage on the CRT, but first you have to determine how the CRT filament voltage is supplied. A simple voltmeter can not be used to measure the filament voltage. These sets get that voltage from a winding on the horizontal output transformer. There are two cases: 1) the winding directly feeds the high frequency AC to the filament [usually through a low resistance voltage dropping resistor of 2 - 5 ohms], or 2) the voltage is rectified and filtered with a capacitor and DC is fed to the filament [again possibly through a dropping resistor]. If yours is AC fed, Bridge the dropping resistor with one of equal value and see if that helps. If so, you can leave the resistor bridged and coax a bit more life out of the set. If it is DC fed, check the filter capacitor for high ESR or just replace it. If that helps your are done, if not, try bridging the dropping resistor as above.

David

Thanks all!!!! I'm convinced.