Do you see any change on the screen at all when
you change from channel 6 to channel 7 ?
If so, then the band switching is probably working and the
microprocessor is probably communicating with the tuner.
In that case I would look to see if the tuner is getting
the 30-33 Volts it needs for tuning.
Also, to test the RF amp in a tuner,
you can float the AGC pin, then if you use one
hand and touch this floating pin with one finger, you can
then touch some point in the circuit that has about 8 volts
and up with another finger ( on the same hand), or you
can touch the other finger to ground.
By doing this, you can actually set the AGC voltage of
the gate of the preamp mosfet to just about any voltage
you want without the need for an external voltage supply.
It's a good idea to touch some ground point in the set first
(tuner can itself) and discharge any static electricity from
you body first as you will be directly handling the gate
of the preamp mosfet when you do this, and you don't want
to spike the gate with a charge of static electricity that may
punch through the gate.
Any voltage in excess of 20 volts might do this.
Some of the newer mosfets can handle up to 30volts on
the gate, but doubtful that this would be the case for
the small RF amp type mosfet devices used in tuners.
So what I usually do is discharge my body by touching
the tuner can, then I find a pin on the tuner that is something
like a 12V B+ supply, and use that for the "hand conducted"
voltage source.
Usually, to test the RF amp in the tuner, I simply try two things.
1,, pull gate of the RF amp up to 12V by touching 12 V
2,, pull gate of the mosfet down to ground by touching ground.
The tuner should be snowy when pulled down to ground and
look good when pulled up to 12V.
There,, there's a simple "hands on" approach to testing the
RF amp in the tuner
