Every third off-hook (intercom or outside line doesn't matter) results in extremely low volume level in the handset, both sides of conversation, any/all terminals. I assume that there is a three-channel audio crcuit in there somewhere that gets selected in sequential order with each off-hook, and that one of the channels is bad. My question is which module do I need to replace? I assume the 61330A processor but would like confirmation. Thanks, Bill Martin