I have a Smile/KFC Monitor, Model CB1414VL

At Start the Power Supply MosFet was blown (really), I replaced It and the KA3842A.

When I power it nothing heapens.

I've made some tests and the power to KA3842A, is always going up and down from 11V to 14V.

I have replaced some broken resistors and some Capacitors (that I don't know If they were bad), but I've seen that solution elsewhere to solve this kind problem.

Now I don't know what to do more. I'm stuck.

Best Regards

Did you check the low value resistor in the source of the fet.

Usually 0R33 to 0R47 at 2W.

Rich

I replaced that one, I think it is an 0R22.

I replaced the diode at the gate of the Fet and checked almost every compunent arround...

Don't know what to do more.

Best Regards.

The voltage on pin 7 must go above 16V for the IC to start,the electrolytic on pin 7 has to supply the increased current to pin 7 until the psu starts up and produces the continuous rail for pin 7. If the psu fails to start the voltage on pin 7 drops below the UVLO level and the start up sequence begins again.

So I guess that you may have excessive load on the output.

Rich

So what can be wrong.

What can I test after?

I've no experence, I'm now trying to learn something more about monitors.

Best Regards

There are lots of items that can cause excessive load.

Short circuit diodes in the psu.
Short circuit HOT (Horizontal Output Transistor)or parallel diode.
Failed frame output IC or Video IC or output transistors.
Failed FBT

This is a few of the more common monitor failure items.

Rich

Now I'm stuck for good.

Some of that expressions realy exceed my knowledge about monitors.

"Short circuit diodes in the psu." -> If they are arround the power supply MosFET and the KA3842, I have tested all compunents, including resistors. With all the replacements I made, I think that no one is short.

"Short circuit HOT (Horizontal Output Transistor)or parallel diode."
-> Where is it located? What are the normal refereces for it?

"Failed frame output IC or Video IC or output transistors."
-> Don't know what/where they are, can you help?

"Failed FBT"
-> Not a Clue, Can you help, again?

Sorry, but in this kind of subject I'm realy a rockie, I'm now starting to learn.

This forum is realy nice, and seams that are realy nice users too.
I hope someday I will be able to help someone too.

Best Regards.

Are there anyone that can give-me some hints?

I've removed the Flyback from the board and the monitor does exacly the same as if it was their.

I supose that if the flyback was bad the monitor would keep the power on for a while (at least)

Best Regards.