Replace screen taps w/pot Zenith - Videokarma.org TV - Video

TinCanAlley · #1 08-25-2013, 02:22 PM

I've been looking over the schematics for my zenith and it seem that the hi tap is straight through, the medium tape gets a 2K resistor and the low adds another 2K resistor for a total of 4K. Since this setup really doesn't allow for fine adjustments in the grayscale setup (I still see a faint amount of red in the bright areas while watching B&W), would it be possible to replace this setup with a 4K pot for each color?

Thanks!

zeno · #2 08-25-2013, 03:45 PM

Absolutely. There are often pre drilled holes on the
chassis to mount the controls also. Finding the right
value & mounting is the challenge. ( use 5K's)

73 Zeno

TinCanAlley · #3 08-25-2013, 03:59 PM

Quote:

Originally Posted by zeno

Absolutely. There are often pre drilled holes on the
chassis to mount the controls also. Finding the right
value & mounting is the challenge. ( use 5K's)

73 Zeno

Well there are holes, but they're blocked by the heat sinks. If I rotate the heat sinks, the holes are uncovered. Then there's the issue of the transistor sockets. They're pretty close to the holes, so I'll have to find the smallest 5K pot.

I'm assuming the pot should be rated higher than 200V, right? Maybe somewhere near 350V.

TinCanAlley · #4 09-02-2013, 12:45 PM

Anyone know where I can get the connectors like the ones on the tap wires (the white crimped piece)? I'm going to replace the taps with 5K pots and decided the best way to do that, with little modification of original, is to make a piggy back card that will have the pots on the tops side and the plugs on the bottom side. I can then just sit it directly on top of the terminal strip shown in the pic of the post just before this one.

The connectors would sit directly on the HI pins and then the current wires would be connected to pins on the board. I could then more precisely tune them and if necessary, remove it and be back to factory.

Oh, and one more question. I noticed in the schematics that the resistors used in that section are all 1/2 watt. Does that mean I can use a 1/2 watt pot, or should I go higher? There seems to be up to 180V passing through it.

TinCanAlley · #5 09-05-2013, 11:34 AM

Bump....

Found the connectors, but having a hell of a time figuring out what pots to get. Voltage seems independent of wattage in many descriptions. All I know from the SM is that the voltage is 200 and the wattage used for the resistors is 1/2w. Pots I've been looking at range from 1/5w up to 5w and the voltages range from 200V to 500V. I figured a 200V would be good, but then I saw the wattage was only 1/5w. These two things can't be independent, right?

Also, does anyone know of a good source for the pot I'll need? I've looked at mouser and they are between $50 and $120 each. Not only that, but many of the wirewound I've looked for are multi-turn. Don't think I really need 10 turns for adjustment.

So if anyone knows where I can get 5K pots that can handle the 200V from the screen taps that won't exceed the value of the set or burn up shortly after first use, please let me know. Want to get this right the first time.

Thanks