Question about Radio Communications
First thing to try is to read the DC voltage with the PTT pressed on Pin 2 of the RF amplifier "brick". It should be somewhere around 6 volts. If it's way high or zero, it's likely that yours is one of the victims of a design flaw wherein Q19 on the underside of the main board (and right next to Pin 2 of the RFPA module) fails. It usually fails due to heat. It's a well-enough problem that, were you to send it in to Icom for repair, it would likely be repaired and have an undocumented heat sink panel affixed to its back. For awhile, an internal memo at Icom service instructed techs to make the repair and blame the failure on high antenna system SWR, and then charge the customer big $$ for it. Incidentally, when the radios come back, they now have that little heat sink installed on the replacement transistor.
I've had 6 of these radios come across my service bench for that very problem. It's a pretty easy fix once you know to look for it.
BTW, it's also possible that one of the PIN diodes in the T/R switch has failed open, but not nearly as likely as Q19.
I've also found the stock chassis heatsink fin area to be insufficient to dissipating the heat from even medium power operation, so for my own radios (I've got 4 of these in service) I have put quiet 12 vdc muffin fans on the heat sinks to help keep the radios running cool. Many users believe the relatively massive heatsink area of the outer chassis is enough to dissipate the heat produced by the final PA block, but any time I can't stand to rest my hand against a heat sink because of its temperature, I have to wonder just how badly the components producing that heat are suffering, so I opt for the fan.
HTH es 73,
Posted on Jan 01, 2017
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Posted on Jan 02, 2017
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