Kortek KT-3301 pincushion problem.

[Arm123]

Anybody work on one of these before ?



I have 2 of these chassis...  One works perfectly and the other has a pincushion problem.

As far as i can tell, all the components on boards are identical.  However, the sub board that adjusts the pincushion has no effect on the malfunctioning board.  I have tried swapping the sub adjustment board, where the pincushion pot is located, with no success.  The malfunctioning boards sub board works on the good chassis as well.  So that rules out the sub board.

I have checked and changed most of the caps with no effect.

Any ideas ?

[grantspain]

i have only come up against one particular issue with pincushion failure-the east/west correction diodes,these are normally very close to the HOT.if one goes leaky then the pincushion does not work although adjusting the width will affect it
also i have only ever had this fault on hantarex polo 2 chassis-nearly every one i may add

[Arm123]

hmmm...  thanks for the info Grant.  Ill check and see if the Hrz. width affects the pincushion.

Is there any 'dead giveaway' in locating the east / west correction diodes ?

[grantspain]

hmmm...  thanks for the info Grant.  Ill check and see if the Hrz. width affects the pincushion.

Is there any 'dead giveaway' in locating the east / west correction diodes ?

i would need a schem but usually they are quite beefy diodes located on the collector of the HOT

[Arm123]

Thanks very much Grant.

I'm about to check those diodes this weekend and wanted to ask another question before i got started.

The 'good / working' chassis displays a bit of a problem when it starts up.  The contrast (i think its the contrast, cuz i can make it go away with that adjustment pot) seems to make the colors bleed when the monitor is first turned on.  Then over a period of 60 seconds, it warms up and all goes to normal.

What might cause this ?

[qrz]

Thanks very much Grant.

I'm about to check those diodes this weekend and wanted to ask another question before i got started.

The 'good / working' chassis displays a bit of a problem when it starts up.  The contrast (i think its the contrast, cuz i can make it go away with that adjustment pot) seems to make the colors bleed when the monitor is first turned on.  Then over a period of 60 seconds, it warms up and all goes to normal.

What might cause this ?

if the crt has some age to it , that symptom can be an indication of the tube getting weak.
however,  some NEW crt tv's will exhibit the same for a few seconds.
crt's require a hot cathode to free electrons. it does take a measure of time to go from 0 emissions to full operation

if the delay increases , time to "rejuve" the tube...

qrz

[Arm123]

I have two of these chassis and the other one that has the pin cushion problem doesn't exhibit this behaviour.

Also, i have tested the CRT for emissions and all is well with it.  So i know its not the CRT.

Im wondering if i could be a bad RGB / chroma chip (just speculating) ?  I think it also controls the contrast.

[MonMotha]

Dunno if this model features an auto contrast limit, but it sounds like that could be a possible culprit (settings perhaps drifting as it "warms up").

[qrz]

I have two of these chassis and the other one that has the pin cushion problem doesn't exhibit this behaviour.

when changing a chassis , the crt adjustments will usually need to be aligned 

qrz