k4900 missing blue

paul400

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i swapped out the three main componets with the green and the the blue is still not working.when i turn up the blue all i get is brighter screen but no blue. any thoughts??? tube is verified with another good chassis.
 
took readings at the neck red 66v green 63v blue 174v.
blue doesnt adjust like the others, what does that tell me?
 
You mean that you swapped the color transistors?

Something is defintely out of spec; check everything on the blue circuit.
 
yea, i swapped out the one on the neck and the two on the main board and still no blue, also changed the blue pot.
 
First check that you have blue coming into your chassis. Measure the DC voltage at your video connector compared to the red and green. They should all be the same. Then follow that trace thru Q205 and Q208.

Next make sure you have blue coming into your neckboard. Measure the DC voltage on the blue line as compared to the red and green. All three should be the same.

It's possible you have a problem with the blue gun on the tube. Try a momentary ground jumper to the metal tab of Q403 (on the neckboard) to see if the screen turns all blue. If not, check the tube. If so, check those parts on the blue path as listed in the schematic...
 
First check that you have blue coming into your chassis. Measure the DC voltage at your video connector compared to the red and green. They should all be the same. Then follow that trace thru Q205 and Q208.

Next make sure you have blue coming into your neckboard. Measure the DC voltage on the blue line as compared to the red and green. All three should be the same.

It's possible you have a problem with the blue gun on the tube. Try a momentary ground jumper to the metal tab of Q403 (on the neckboard) to see if the screen turns all blue. If not, check the tube. If so, check those parts on the blue path as listed in the schematic...

Tube tested good with another chassis also shorted neck pin and still good.I will test all the traces and lines
 
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