[Ron Ramirez]

So, Mondial...I went back to the bench and reinstalled the MPX board, but did not resolder the wires as I will be pulling it back out to replace the 25 uF electrolytics with new 27 uF units when I order them.

Before I did that, though, I discovered that sure enough, there was a wire which goes from the Stereo Beacon bulb to terminal 10 on section 1 of the function switch. A wire goes from there to the MPX board.

I removed both wires from terminal 10 and soldered them to terminal 9, which is a dummy terminal (does not connect to anything no matter the position of the function switch). That change made my audio return in FM stereo mode. I still do not understand why Fisher wired the circuit in that manner, but it is also shown in the earlier version (serial number 10000 and up) of the 700-T service manual. My 700-T has a S/N in the 35000 range and I am using the service manual for S/N 30000 and up. It does not make any sense to me why they would apply Stereo Beacon voltage to the feedback circuit of the preamplifier and the equalization circuits only in FM Stereo mode.

Well, anyway...the LED still remains lit no matter what position the function switch is in. One difference: it gets just slightly brighter when tuned to a strong station in FM Stereo mode, then dims slightly when tuned off station. I removed the wire from 4F and grounded it, and the LED lit up brighter than when connected to 4F.

Voltage readings:

TP401 (4G): 2.5 mV (mono), 150.6 mV (stereo) - schematic shows 0.8V in stereo mode.
4B: 4.25V (shows 4V on schematic)
24V source - 24.8V
4F (Stereo Beacon): 21.4V (mono), 20.8V (all other positions)

I think I'll go see if I can find where the hum is coming in on the left channel, while I have the signal tracer out.