Kv-27ts27 color problem

"Joust" bravely wrote to "All" (01 Nov 05 20:46:28) --- on the heady topic of "Kv-27ts27 color problem"

Jo> From: "Joust" Jo> Xref: core-easynews sci.electronics.repair:347167

Jo> i have a KV-27ts27 made July 1992 Jo> I'm noticing that red is more brown than red. Jo> i tried adjusting things a bit but not gotten very good results. Jo> there is no red drive pot. there is a green drive and a blue drive but Jo> no red. Jo> there is a red BKG pot and a blue BKG and a green BKG.

Jo> is there a procedure for tuning color? i made a nice colour bar test Jo> pattern on my PC and use the tvout from the PC into the video 1 input.

Jo> Wish i could get this set tuned up because it works well other than Jo> the poor colors. there is definately red there so its not a failed Jo> gun. at least not completely.

Jo> i have replaced the MPX chip in the past. Jo> any help would be appreciated. Jo> Joust

The drive pots are for the colour gain, an analogy can be made to an equalizer control in audio. Only 2 DRIVE pots tells us that the red gain is fixed. The green and blue pots are used to match up these colours to the red (both typically set at about 1/4 rotation). The drive pots are used to set the colour temperature of the bright white. The other 3 pots are for setting the bias or the low brightness grays. These usually set initially about 1/3 but then more or less depending on the health of the colour guns. A weak gun will require more bias and more drive. At some point though the internal voltages are upset and the gun will both not focus, and converge properly, or even bloom.

I have a monitor with a bad video processor. Colours are saturated with good white and nice gray scale but yellow looks beige as if it didn't have enough red gain.

A*s*i*m*o*v

... I worked hard to attach the electrodes to it.

Assuming the user picture controls work properly and the image is not gray when the color is turned off:

Could be a worn out picture tube that will no longer properly balance or a failure in the video circuitry. You really need to have the video output voltages and drive levels checked to confirm that there is no failure before cranking on controls.

In short, the drives control the high level on the tube and the background sets the low level.

If readjusting:

Depending on the specifics of the model the drives probably need preset to mid control for the blue and green to set the base drive levels the same as the red.

Then turn all three background controls all the way back to minimum.

Apply a black and white gray scale bar pattern on screen. If the set has a service switch then it needs to be set to give a single line across the screen.

Turn up the G2/screen voltage until one of the gun colors is clearly but slightly visible across the screen. If there is no service switch then the 10 IRD gray bar should be used for the background adjustment.

If it is red or green then the other colors background, red or green, needs adjusted to make the line yellow. Then adjust the blue background to make the line as close to white or light gray as possible.

Turn off the service switch and look at the lightest color of gray before the white. Adjust the blue and green drive to make the highlights look as close to gray and white as possible.

Given the age of the set it is probable that the crt will not track properly from low light to high light gray scale. Get it as close as possible.

Otherwise it might be helpful to have a technician do the gray scale adjustment that has lots of experience. They will be able to generally get it close by eye and fudge the adjustment a little even on a weak tube to get a watchable picture.

is there a way to know for sure if the tube is bad? can you measure voltages on the guns or use a scope? I've tweaked these a lot and got no satisfaction.

another question. since its the red drive that needs turned up can a pot be added presumably in place of some fixed resistors that set the red as the ref color.

Yes to the first question. Take the TV to a service shop that has the CRT testing equipment. As far as messing with the resistors NO.. Then you will know for sure and then can get on with your life and replace the TV....After all its only an appliance.