I'm setting up an FR3000 and would like to use the "External Mod B Input" (pin 9 on the 25 pin connector) to inject audio from another receiver's discriminator into the transmit path after pre-emphasis so that it's not preemphasized twice. I can inject a signal onto Pin 10, which injects the signal before the preemphesis circuit and it works just fine, but not matter what I put on pin 9 I seem to get an unmodulated carrier when PTT is activated. I've looked over the service manual in detail and can't figure out what I'm doing wrong. The jumpers on the board seem be placed correctly for the signal path I want. Has anyone used Pin 9? Any ideas what I might be doing wrong?
Thanks in advance,
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