Need help trouble shooting PLL noise on a Tempo 2020
 

I'm in the process of restoring a Tempo 2020 (Uniden 2020). I have
everything working again, but there is one small bug left to swat.
When listening to the receiver I hear a slight gurgle or blip every
few seconds in the receive audio and in the transmitted signal.
I took a general coverage receiver and zero beat the different IF
frequencies in the receiver. All the IF carriers are gurgle free
except the 6.x MHz IF signal generated by the PLL board. The gurgle
or blips in the IF signal generated by the PLL board match the ones I
hear in the receive audio in both time of occurrence and sound. It is
not constant, but it may happen three of four times within five
seconds.
I tapped around the circuit board with a pencil, and noticed a
similar noise when I tapped around resistor R812 and C815. I replaced
those two parts, but it did not make any difference. D807 (part #
mv201) is a varactor diode in the same vicinity, and I'm suspicious of
it. Any helpful suggestions would be appreciated

There is a schematic of the Tempo 2020 PLL board on-line at;

http://www.shadowstorm.com/cb/schema...-pll-board.jpg.

Thanks,

-Rea

On Mon, 11 Apr 2005 02:36:50 GMT, (Rea) wrote:


I'm in the process of restoring a Tempo 2020 (Uniden 2020). I have
everything working again, but there is one small bug left to swat.
When listening to the receiver I hear a slight gurgle or blip every
few seconds in the receive audio and in the transmitted signal.
I took a general coverage receiver and zero beat the different IF
frequencies in the receiver. All the IF carriers are gurgle free
except the 6.x MHz IF signal generated by the PLL board. The gurgle
or blips in the IF signal generated by the PLL board match the ones I
hear in the receive audio in both time of occurrence and sound. It is
not constant, but it may happen three of four times within five
seconds.
I tapped around the circuit board with a pencil, and noticed a
similar noise when I tapped around resistor R812 and C815. I replaced
those two parts, but it did not make any difference. D807 (part #
mv201) is a varactor diode in the same vicinity, and I'm suspicious of
it. Any helpful suggestions would be appreciated

There is a schematic of the Tempo 2020 PLL board on-line at;

http://www.shadowstorm.com/cb/schema...-pll-board.jpg.

Thanks,

-Rea


If the the link above does not work it is because I accidentally
included a period at the end of the hyperlink. Try the link below.

http://www.shadowstorm.com/cb/schema...-pll-board.jpg

I fixed it! The problem was voltage regulation from the AVR board
(automatic voltage regulator). The pots (R659 and R653) had oxidized
over time and were making irregular connections. The voltage
fluctuations were causing the PLL board to randomly wobble one of the
IF frequencies (6.3 MHz, 6.4 MHz, 6.5 MHz, 6.6 MHz, and 6.7 MHz
depending on the selection from the front panel segment KHz buttons).
I cleaned the pots on the AVR board with contact cleaner, and set the
voltage back to 5.0 volts and 8.2 volts as specified in the Tempo 2020
alignment manual. The PLL IF stabilized and appears to be working
normally now. The frequency warble in the PLL IF carrier is gone, and
the audible warble in the receive and transmit audio is gone as well.

-Rea

On Mon, 11 Apr 2005 02:40:12 GMT, (Rea) wrote:

On Mon, 11 Apr 2005 02:36:50 GMT, (Rea) wrote:


I'm in the process of restoring a Tempo 2020 (Uniden 2020). I have
everything working again, but there is one small bug left to swat.
When listening to the receiver I hear a slight gurgle or blip every
few seconds in the receive audio and in the transmitted signal.
I took a general coverage receiver and zero beat the different IF
frequencies in the receiver. All the IF carriers are gurgle free
except the 6.x MHz IF signal generated by the PLL board. The gurgle
or blips in the IF signal generated by the PLL board match the ones I
hear in the receive audio in both time of occurrence and sound. It is
not constant, but it may happen three of four times within five
seconds.
I tapped around the circuit board with a pencil, and noticed a
similar noise when I tapped around resistor R812 and C815. I replaced
those two parts, but it did not make any difference. D807 (part #
mv201) is a varactor diode in the same vicinity, and I'm suspicious of
it. Any helpful suggestions would be appreciated

There is a schematic of the Tempo 2020 PLL board on-line at;

http://www.shadowstorm.com/cb/schema...-pll-board.jpg.

Thanks,

-Rea


If the the link above does not work it is because I accidentally
included a period at the end of the hyperlink. Try the link below.

http://www.shadowstorm.com/cb/schema...-pll-board.jpg