[Ron Ramirez]

Now, while I was down in the basement a little while ago taking the photos in my previous post, I decided to do some further testing. I removed the output and driver transistors, turned the receiver upside down, and brought the unit back up on the Variac.

I had it tuned to an FM station as it turned out, and as I turned up the voltage, the signal meter slowly swung to the right and the Stereo Beacon lamp (converted to an LED already) came on.

I had my signal tracer ready, so I looked for an audio signal at the predriver.

Nothing.

I went back to the preamplifier.

Nothing.

I turned it off, flipped it right side up, turned it back on again, and checked for audio at the output of the IF board.

Bingo - there was mono audio.

To make sure the cable between the IF board and the MPX board was OK, I checked for audio at the input of the MPX board.

Yup, still there. But there is nothing at the L and R outputs of the MPX board, and nothing at Test Point 402 (Mono).

So the signal gets to the MPX decoder board, but is cut off there as there is zero output from the MPX decoder.

Side note: The Stereo Beacon LED stays on whether the set is tuned to a station or not.

This ought to be fun to figure out...not.