Could be a bad IRF510.
I would put a 1 amp fuse in your 12v power supply line, monitor the power supply current
so you know if that IRF510 is suddenly taking off.
With PTT pressed, verify that the drain of that IRF510 has 12v dc.
Slowly turn that bottom pot (RV2 or RV3) counter-clockwise while
monitoring gate voltage of the associated IRF510, the gate voltage should go up from
zero volts toward 5 volts.  Somewhere around 4 volts the drain current will suddenly rise
if the IRF510 is any good, do not go any higher than perhaps 200ma.

If you never see the rise in drain current, that IRF510 is probably blown.
If some bad connection is momentarily restored somewhere, that IRF510 could
burn out in a second or two with 5v on the gate and no 1 amp fuse..
In normal use, perhaps a 3 amp fuse would be about right.

Jerry, KE7ER



On Wed, Oct 7, 2020 at 07:33 AM, Praba Karan wrote:

I have noted no transmission from my ubitx V3.
But Rx is working nicely.
I noted following observations during my troubleshoot.
1.during Rx - current draw 300ma
2. During PTT - current draw 500 ma
3. during PTT with loud halllow - current draw 600ma.
4. Adjusting bottom pot ( RV2 or RV3) have no effect on current consumption to PA (contrary to upper pot.)
5. During adjusting PA bias, no heating noted in left IRF510 even at full clockwise position of bottom pot. ( Contrary to right IRF510).

Can I assume that one of final irf510 went QRT? 

Hello Jerry i think  5 volts on gate is very to hight  i have 4 v on gate of my Ubbitx  V3 73’s jo f6cht.

 

Provenance : Courrier pour Windows 10

 

I agree.   In my message I wrote:
#  Somewhere around 4 volts the drain current will suddenly rise
#  if the IRF510 is any good, do not go any higher than perhaps 200ma.