Hi all,

About a year ago I did an attempt to repair a Sony KV-4SV2. Which I could not fix: viewtopic.php?f=3&t=415231

I recently bought another one, which seems less damaged by the leaky caps.

I started to replace bad caps and cleaned all the boards.
Once I turn on the TV, I get a horizontal white line.

What is the safest way to further troubleshoot ? I cannot keep it turned on more than a few seconds (as I don't want to burn the tube).

I tried reducing brightness and SCREEN but it remains very bright.

In order to further proceed I would need to have the TV turned on and use the scope to see what is going on.

Thanks all

Disconnect the CRT's heater/s, so that there is no electron emission from the cathodes. That will save the phosphor. It should not affect the vertical circuits that you are fault finding with the scope.

One other method is to disable the EHT and line scan, by disconnecting the collector of the H output transistor, or, shorting out its base-emitter connections to kill its drive. This kills the EHT and line scan and power to the video output stages usually. However, in some TV designs, the auxiliary voltages from the line OPT transformer are used in other places in the set, and that can cause some issues.

Yet another method would be to look at the CRT's grid circuit and see if there is an easy way to apply 30 or 40V negative to help cut off the beam.

Thanks for the suggestion, I see there is a resistor on the CRT neck board with the H1 line, I will just disconnect it.

Or just leave the CRT socket unplugged.

Oh yes that's even easier.
Are those sets known for bad vertical deflection IC ?
For now I suspect something on the D3 board as this one was the most eaten by electrolytic fluids.

I have never seen a bad vertical IC on one of these. It's probably just an open trace, or via. Start by checking the supply voltage to the vertical IC on the D4 board.

I didn't suggest unplugging the CRT socket, because there are high voltages on it and then its is dangling somewhere. If you do unplug it, wrap it up in a plastic bag so it won't short out or arc over to anything nearby.

Indeed I put s plastic bag on it to avoid any contact / short with something else.

So there is indeed something wrong with the 12v and 9v lines feeding the vertical IC.
I will further troubleshoot but looks like the problem already starts in D2 board.

Probably an open trace somewhere. The power supply usually has the most damage.