Repair attempt of marantz 2240b with "no FM stereo" symptom.

Common symptom, but this one has a far bigger underlying problem. Many are quick to jump to the HA1156w multiplex decoder IC because its readily available, or they replace the lamp because in some designs the lamp has to be good for the multiplex to start. No so here. In many later marantz designs, the muting circuit is responsible for the audio output muting between stations, as well as controlling the command line to start or stop the multiplex. The tell is to turn the FM muting on. If the FM now goes silent, look to the muting circuit. If it does not, then we have to troubleshoot the multiplex. In this scenario, the multiplex internal VCO is operating, taken from a test point, and the signal coming out of the detector is sufficient, and the signal strength at the meter is sufficient. The voltage at the control transistor that turns muting off and MPX on is missing. lets try and find out why.