Kortek Monitor no vertical deflection (By Belbenchtech)

[SAT (aka GANDHI)]

wgallo3193 wrote:

I have a cortex monitor that has no vertical deflection.

I have recaped it and also replaced a shorted deflection driver and open resistor to the same. I have no schematic so Im working on it blind. It seams the problem is no input from the LA78XX chip (dont remember number), I swaped it with another but still no output on pin 7.

I do not know the model number. It has a swithing power supply and is a 23 inch display I think.

Has any one had this trouble? Star tech has it listed but I am not a member. Any light you can shine would be very apreciated.

Thanks, Bill

[SAT (aka GANDHI)]

Belbenchtech wrote:

Hi Bill,

Are you sure the monitor you're working on is a Kortek?  The reason I ask is the LA78XX chip you spoke of sounds a whole lot like a Ceronix monitor...just went through my Kortek CD and didn't find any schematic for a 23" monitor.

I've never worked on a 23" Kortek monitor and don't have schematics for that size...chances are that it is similar to the rest of the Kortek family of monitors (manufacturers USUALLY don't change much from one monitor size to another size).

My best advice is to check all of your voltages, make sure they are all there, if so then the vertical sync coming into the monitor, if the vertical sync is present move to a point about half way through the vertical circuit and check for sync again...keep doing this (divide and conquer) until V. sync is lost, then backup one component at a time until V.sync is reacquired...change the component last tested.

Sorry, I'm not of more assistance to you, if you can post more info I'll try again...
Mike><>

[SAT (aka GANDHI)]

wgallo3193 replied:

Here is an up date on my problem

This board may not be a Kortex but it sure looks like one. The Ic on the bd is a LA7832 and it has a long .156 connector that leads to a remote controll board.

I have found the problem with no vertical deflection. It was an open at a solder joint leading to pin 8 of the LA7832. Now I have deflection but not full deflection, (about 2/3 screen) and the picture has fold over. I have checked all associated caps surrounding vert out IC and H/V IC but all are good. I'm thinking that I may have a fly back problem. Have you ever seen a fly back cause this?

Thanks for your help!

[SAT (aka GANDHI)]

channelmaniac said:

I haven't...

I have seen a leaky diode cause that on a couple of different makes/models of VGA monitors for computers. Back in the day when they were worth fixing... Wink

Many of the monitors out there derive the voltage for the vertical deflection from a tap off of the flyback. It'll go through a resistor (pretty much just used as a fuse) and then to a diode.... then a cap... then to the vert deflection IC.

Not sure if yours is set up the same but it probably is. If the voltage level is low then check the resistor to see if it changed value and replace the diode to see if the voltage comes up.

RJ

[SAT (aka GANDHI)]

wgallo3193 concluded:

Thanks RJ and Mike - I have solved the problems

The board is set up as you stated RJ and that area I repaired early on. The driver IC was shorted to start. After repairing that I still had no deflection and found that I had a connection problem at pin 8 of the LA7823 ic after that the deflection was rolling over and only 2/3 screen. The deflection role over was affected by the brightens controle and I had no contrast controle. I thought a power problem because levels seamed low but it was not. It was a problem in the video processing chip a UDP2XXX. I replaced it from a old board because no cross was available and bingo. That was the last of the problem.

Note that this monitor has a plug in controle board that must be attached for any vertical deflection.

I hope this will help others in the future.

Thanks, Bill