04-04-2014, 07:45 PM
C O R R E C T I O N
After further testing, I have to revise my previous comments.
A second test proved that I was indeed getting audio at the L and R outputs of the MPX board.
Now, here is where it gets really interesting.
With the function switch in either the FM AUTO or FM MONO positions, audio gets all the way to the inputs of the driver boards, and it is quite strong indeed.
With the function switch in FM STEREO...nothing. Dead. The signal is lost at the preamplifier; very weak at the preamplifier input, nonexistent at the output.
As an aside, I am getting a hum in the left channel at the input to the left driver board that is not present at the input to the right driver board.
One more thing. With the function switch in either FM AUTO or FM MONO, the Stereo Beacon dims somewhat but remains illuminated whether the set is tuned to a station or not. It remains illuminated when the unit is set to PHONO or AUX. In the FM STEREO position, it gets brighter and stays bright, whether tuned to a station or not.
Through all of this, I realize that the load of the driver and output transistors not being present may, or may not, have an effect upon these tests.
Click the thumbnail below to see the schematic for this set.
[Image: http://www.philcoradio.com/images/phorum...ematic.jpg]
After further testing, I have to revise my previous comments.
A second test proved that I was indeed getting audio at the L and R outputs of the MPX board.
Now, here is where it gets really interesting.
With the function switch in either the FM AUTO or FM MONO positions, audio gets all the way to the inputs of the driver boards, and it is quite strong indeed.
With the function switch in FM STEREO...nothing. Dead. The signal is lost at the preamplifier; very weak at the preamplifier input, nonexistent at the output.
As an aside, I am getting a hum in the left channel at the input to the left driver board that is not present at the input to the right driver board.
One more thing. With the function switch in either FM AUTO or FM MONO, the Stereo Beacon dims somewhat but remains illuminated whether the set is tuned to a station or not. It remains illuminated when the unit is set to PHONO or AUX. In the FM STEREO position, it gets brighter and stays bright, whether tuned to a station or not.
Through all of this, I realize that the load of the driver and output transistors not being present may, or may not, have an effect upon these tests.
Click the thumbnail below to see the schematic for this set.
[Image: http://www.philcoradio.com/images/phorum...ematic.jpg]
--
Ron Ramirez
Ferdinand IN
