Re HDTV Teac cm-687 is this what I should try?
 

re post 18/7/2005
Thank you all.
I would like to do this test but I need to check about correct
procedu would it be proper to solder a 3.9 zener diode with the -
end to the tuner's AGC pin and the + end to the tuner's ground.
I understand the idea is to clamp the voltage to 3.9; is this right?
I will wait for confirmation.
Al.

alitonto wrote:
re post 18/7/2005
Thank you all.
I would like to do this test but I need to check about correct
procedu would it be proper to solder a 3.9 zener diode with the -
end to the tuner's AGC pin and the + end to the tuner's ground.
I understand the idea is to clamp the voltage to 3.9; is this right?
I will wait for confirmation.

That would be the proper way. To make sure, check that the AGC line
actually contains a resistor so as not to short anything with the zener
diode. Then connect the zener directly between the tuner pin
(cathode) and the ground (anode).

---
Met vriendelijke groet,

Maarten Bakker.

wrote:
alitonto wrote:
re post 18/7/2005
Thank you all.
I would like to do this test but I need to check about correct
procedu would it be proper to solder a 3.9 zener diode with the -
end to the tuner's AGC pin and the + end to the tuner's ground.
I understand the idea is to clamp the voltage to 3.9; is this right?
I will wait for confirmation.

That would be the proper way. To make sure, check that the AGC line
actually contains a resistor so as not to short anything with the zener
diode. Then connect the zener directly between the tuner pin
(cathode) and the ground (anode).

---
Met vriendelijke groet,

Maarten Bakker.

Thanks Maarten
I now must say that the AGC pin from the tuner is connected directly to
the pin of the I/C; no resistor is connected in series between the 2
pins.
However there is a couple of resistors off this line therefore in
parrallel. Is this still okai to do the test?
Thanks for your input.
Al

alitonto wrote:
I now must say that the AGC pin from the tuner is connected directly to
the pin of the I/C; no resistor is connected in series between the 2
pins.
However there is a couple of resistors off this line therefore in
parrallel. Is this still okai to do the test?

There is a risk of blowing up the IC. Disconnect the tuner pin and use a
variable power supply directly to the AGC pin of the tuner. Or use a 9V
battery with a 10k variable resistor.

---
Met vriendelijke groet,

Maarten Bakker.