Sorry for the obvious that follows, but it has happened to me before hahaha. There is a MOX knob that puts the radio in transmision without pushing PTT. If it is pushed in, the radio goes in TX without PTT. Maybe it can happen too with the VOX. Of course to go into TX has to be in HAM mode. So if any of the events are "ready" as soon as you go in HAM the radio goes on TX. So check that you dont have MOX or VOX ready to activate TX.
In case the radio goes on TX when in HAM, you lose reception. As I told you it had happened to me during repair. ?Why does it not receive? SILLY it was in transmission? because MOX was ON. Some modes FM FSK or CW can produce full power
Because the PA (alias "the brick") has only 3 connections, 24V for finals, 13,5V for drivers, and (switched RX/TX) TX13.5V for predriver Q01 and bias 13,5V>8V>0.7V with the two voltage regulators. It is very pasive just follows the orders, but has no decision.
You can test the PA outside the radio. and measure intensity. TX13.5V in mine was about 200mA. 24V for finals, and 13.5 for predrivers should be almost 0 without TX13.5V (reception). I have not measured intensity because mine worked OK, but I think that 24 and drivers should take about 1A each in TX (no signal out) and nothing in RX.
Check voltage out of Q01 in RF unit in RX and TX with PA out. That is the TX13.5V output to PA.
It inhibites (cuts) TX13.5V in GEN and allows transmission in HAM, I mean ALLOWS, because RL01 in RF unit is the one really switchin RX/TX. In a very brute way Q01 in RF unit can be bypassed, it only inhibites in GEN or TRANSVERTER, in other words KILLS the PA even if RL01 goes in TX, RF unit Q01 stops TX13.5V to the PA. As all is OK in GEN, I think Q01 in RF units makes its job cutting TX13.5V from RL01, even if RL01 moves from RX to TX, Q01 stops 13.5V to PA. Only when Q01 in FREE (HAM mode) you get the problem. You have to check Q01 output. If you get 13,5V in HAM RX the problem is in RL01 ?welded allways in TX? I think this is the first thing to do, and it is easy. Just disconnect the PA and open the low cover to have access to RF unit.?
As you see, nothing should change in PA unit as long as the radio keeps in RX.
Check MOX and VOX. and relay RL01 in RF unit. Maybe does not cut TX13.5V out in RX mode. Easy to check in Q01 in RF unit. just in a front corner, a large transistor, acting just as a switch.
Even so, you have a problem, because even in TX should not smoke. So when (AFTER) you clear the first part (RX/TX switching), you have to check the PA. I think something makes drivers and finals high intensity. Maybe some are damaged (short collector-emmiter) or bias that should be about 0,7V from second regulator, is extremelly high ?8V? and makes drivers and predrivers crazy.
I have repeated myself a lot hahaha, but I think the message it is clear.
73 EA1FC
