ICOM A200 intermittent transmit failure

We are chasing a very occasional ICOM A200 transmit issue. We found one issue that caused a hard failure (PTT connection at rear seat stick). A new connector resolved that. Now, we have a very occasional Issue where you squeeze the mic button (trigger switch), the intercom transmit light lights up but there is no sidetone or transmission. It doesn't matter which headset we use (tried three) We've checked the switch, cleaned and reseated the intercom connector. Did the same for the ICOM. The problem may go away for 10-20 hours and then come back. Five minutes later, it's working fine again and may not fail for many flights. Seems that I read somewhere, way back, about someone having this issue and it was a resistor that was used as a jumper that was breaking connection in a way that was difficult to see. If anyone remembers anything about this, could you please give me a hint where to look.

Thanks for any info.

I once had an intermittent tx problem which was traced back to high resistance in a breaker switch. Suggest check voltage at the radio...