AGC Tuner problem

[John Q]

Hi , I'm working on a combo TV/VCR SAMSUNG CXD1333.

I have a problem with the RF signal .

On video cassette , picture is OK.

With the RF signal , picture is very very snowy...Can see only a little bit
but too snowy to watch.

On the tuner , I have a steady 5 and 33 volts. On AGC , stay at 0.16 volts
all the time , even when removing the antenna.

I trace the AGC signal to an IC (SEC KA2163) to pin 5 and still 0.16
volts.This pin is called "RF AGC".

On pin 3 of the same IC , it's called IF AGC ang I have 7.79 volts.

How can know why AGC is not changing at all.

My next step will be to inject a voltage to AGC input of the tuner to make
sure the tuner is OK.

Any idea ?

Thanks...

 

[Sofie]

John Q:
Probably NOT an AGC problem but more than likely a bad RF amp and/or some
other components in the front end.
Look for the obvious cracked solder connections on the tuner module pcb and
where the shielded box is soldered to the tuner pcb. It will probably be
much easier and might even cheaper to just replace the tuner module.

 

[Bentech]

Hi ,

Thanks for your reply...I should not have a AGC voltage to the tuner at
least ? I had openned the tuner and resoldered all connections and
samething...