John,
ok, If the current is flowing from 5 V trough the PA transistor, the current on 5 V could be around 200 mA and the heat power 1 W or so. This is much more than 60 mW and will clearly heat up the PA. It would be good to know the Duty cycle for 5 V (Terminal Diagnostics).
If the fault current is flowing via the 5 V some of the outputs of IC503 have to be ON. So IC503 could be faulty in this case. But I guess, not the whole IC503 is faulty because the PA is working partially.
An other possibility would be if the signal "TX" to IC503 is not LOW and so one pair of BS170 is ON the whole time. It depends also on the signal "CLK2" to IC501 and IC502. Are there pulses in RX mode?
Not so easy to predict the faulty part.
73, Ludwig
