Sony KVM1430A low contrast

[bigboss80]

Originally Posted by vol.2

It's out of spec and should be replaced, but it is unlikely to be the problem with your set. It's 70% of spec which is almost certainly not going to bring a whole portion and the circuit to its knees.

If there is something wrong with your set that it not just the CRT tube failing, then you will probably be able to find a problem with something in the service manual. There should be voltages listed all over the place, and possibly waveforms to check with an oscilloscope. Sony was pretty good with the waveforms, and a Sam's should have them too.

First order of business is to verify all of the power supplies. TVs tend to have a bunch of supply sources taken from both the initial power supply of the sytem, and also some derived from flyback pulses. Check all of them.

Once you've done that, start checking voltages on ICs and make sure everything is correct.

Then check all the waveforms.

At some point, you'll find an issue.

Keep in mind that voltages and waveforms are specified with a specific input condition, like a color bars input or a window input, etc.

What you have displayed on the screen will change voltages in many places, and waveforms in many places.

I don't have an oscilloscope, nor a color bar generator, I use a DVBT with color palette as a generator, from what I understood by reading R812 it is part of the ABL (Automatic Brightness Limiter) circuit, but I don't know if I misunderstood the diagram