A faulty in vehicle DCDC charger has fed 16V or so into my brand new IC7100, killing the main board and preventing it from transmitting. I've replaced the mainboard with a brand new one however I'm stuck with an non-transmitting PA board.

I've noticed, if I configure the radio at 7Mhz FM, I get a good carrier at the gate of the drive amp, however it's Vpp is 5V which I don't believe is enough for the drive amp MOSFET (Q251) to conduct, thus there is nothing driving the TX stage. I'm not exactly sure how the DRIDV bias works however I'm not measuring anything from the ribbon connector from the mainboard during TX (EP721).

What's the purpose of the "TX drive AMP idling current control" and what would be it's expected behaviour with no measured output? Should it's voltage be additive with the output of the earlier staged drive pre-amps?

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  • $\begingroup$ You have had no answers it seems. I am chasing a related fault and came across this. So curious about your figures I measured mine as it is open on the bench. Q251 I have 13.5V on the drain all the time, and a bias of 3.2v on the gate on TX. It is worrking ok. Hope that helps but I doubt that at 6 months ago post you still have it in fault cndx. Cheers ZL3OZ $\endgroup$
    – Ken
    Dec 28, 2021 at 4:23
  • $\begingroup$ Hi Ken! This was a hassle and a painful repair. After talking to Icom about the fault they said that the PA board lost its calibration and the radio needed to be recalibrated. Having returned the radio to them for said calibration they decided that the PA board was fried and needed to be replaced (which I'm not so sure about) however it was fortunately done under warranty $\endgroup$ Jan 11, 2022 at 3:23


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