Disabling Sharpness Control on a Sony

[vol.2]

I am looking at my KV-9PT20, and it's got not Sharpness control, but the jungle chip has Sharpness. I'm assuming that Sony just set the Sharpness to be permanently at a specific value, and judging from the picture, it's not "off."

I'm wondering if there's a way to either remove the Sharpness from the circuit totally in order for it to be "off," or to add a Sharpness control.

Thanks for any ideas here.

The jungle IC is the LA7672:





And on the schematics:

[KPackratt2k]

My suggestion would be to replace R212 (and R214, if necessary) with different values to see if it makes any difference in the sharpness of the image.

Try removing R212, run wires from its pads (or nearby pads that connect accordingly to the schematic) to a breadboard, place a 20k-50k ohm potentiometer on the breadboard, connect those wires to the potentiometer on the breadboard's lines, and adjust it while the set is on to see if it makes a difference. If this allows you to adjust the sharpness and you have it to your liking, measure the resistance of the potentiometer at its ideal position, find a replacement resistor that matches its value (I assume you'll need an 0805 SMD resistor judging by what I remember from the last time I opened mine up), and replace R212 with it.

If temporarily replacing R212 with a potentiometer doesn't make a difference, then remove R214, run a wire from chassis ground to the breadboard, place another 47k-50k ohm potentiometer onto the breadboard with one side wired to the R212 path closest to the jungle chip and the middle wired to a 10k ohm resistor to ground (so you don't accidentally ground the 9V rail during testing), and adjust both potentiometers while the set is on. Once you have the sharpness at a desirable position, measure the resistance of both potentiometers (measure between the side leg of the second potentiometer and the ground side of the 10k ohm resistor on your breadboard to get an accurate reading, order replacement resistors that match the values of your measurements, and place them where the two removed resistors used to be on the chassis.

I haven't tried this personally, so I can't comment on whether or not it would work, though my hunch is the value of the sharpness is controlled by the voltage the pin is receiving, so it's worth a shot to try it. I'd match the values of the breadboard potentiometers to the original resistor values before you turn the set on and make slight adjustments to be safe, in case receiving an excessive voltage can hurt the chip.

The measurement circuit can be simplified as:

Jungle chip sharpness control (side of R212 closest to jungle or a nearby component connected in its circuit) -> Side legs of both 50k ohm pots (or just one if you're only testing R212 first before testing both, depending on whether it would be necessary or not).
Center leg of 20k-50k ohm pot #1 -> 9V rail (where the other end of R212 connects).
Center leg of 47k-50k ohm pot #2 -> 10k ohm resistor -> ground.

EDIT: For what it's worth, I've just replaced R212 with a 22k ohm resistor on my KV-9PT20 and saw a noticeable improvement once I tested the set afterwards. I no longer see a sharpness effect on the neither the stock Composite input nor the S-Video input mod that I did to it and it didn't appear to affect image definition. Maybe a resistor in the 15k-22k range might be the magic bullet here.

[vol.2]

My suggestion would be to replace R212 (and R214, if necessary) with different values to see if it makes any difference in the sharpness of the image.

Try removing R212, run wires from its pads (or nearby pads that connect accordingly to the schematic) to a breadboard, place a 20k-50k ohm potentiometer on the breadboard, connect those wires to the potentiometer on the breadboard's lines, and adjust it while the set is on to see if it makes a difference. If this allows you to adjust the sharpness and you have it to your liking, measure the resistance of the potentiometer at its ideal position, find a replacement resistor that matches its value (I assume you'll need an 0805 SMD resistor judging by what I remember from the last time I opened mine up), and replace R212 with it.

If temporarily replacing R212 with a potentiometer doesn't make a difference, then remove R214, run a wire from chassis ground to the breadboard, place another 47k-50k ohm potentiometer onto the breadboard with one side wired to the R212 path closest to the jungle chip and the middle wired to a 10k ohm resistor to ground (so you don't accidentally ground the 9V rail during testing), and adjust both potentiometers while the set is on. Once you have the sharpness at a desirable position, measure the resistance of both potentiometers (measure between the side leg of the second potentiometer and the ground side of the 10k ohm resistor on your breadboard to get an accurate reading, order replacement resistors that match the values of your measurements, and place them where the two removed resistors used to be on the chassis.

I haven't tried this personally, so I can't comment on whether or not it would work, though my hunch is the value of the sharpness is controlled by the voltage the pin is receiving, so it's worth a shot to try it. I'd match the values of the breadboard potentiometers to the original resistor values before you turn the set on and make slight adjustments to be safe, in case receiving an excessive voltage can hurt the chip.

The measurement circuit can be simplified as:

Jungle chip sharpness control (side of R212 closest to jungle or a nearby component connected in its circuit) -> Side legs of both 50k ohm pots (or just one if you're only testing R212 first before testing both, depending on whether it would be necessary or not).
Center leg of 20k-50k ohm pot #1 -> 9V rail (where the other end of R212 connects).
Center leg of 47k-50k ohm pot #2 -> 10k ohm resistor -> ground.

EDIT: For what it's worth, I've just replaced R212 with a 22k ohm resistor on my KV-9PT20 and saw a noticeable improvement once I tested the set afterwards. I no longer see a sharpness effect on the neither the stock Composite input nor the S-Video input mod that I did to it and it didn't appear to affect image definition. Maybe a resistor in the 15k-22k range might be the magic bullet here.

Awesome. Thanks so much for experimenting with this. I knew it had something to do with the value at pin 33, but I didn't know what would do that because there are so many other things connected to it. After reading your explanation, it seems obvious that it would be a resistive divider altering the voltage on the IC pin, but I guess I was worried it might have some effect on the other side of the circuit where the inductor is.

I'll setup a breadboard and see if I can't get it to be tuned in and report back with the value that seems best on my set. It's totally possible that the sweet spot will be a little different, depending on the set. I have Wii 240p Test Suite, so I can use the Sharpness Pattern in that over S-Video and dial it in good.