Q9 is in parallel with Q11. They are supposed to share the load equally. Perhaps Q11 is defective as an open circuit, or poorly soldered, or just has a much higher than normal on resistance so that Q9 takes all of the load.
Replace Q11 as well, and verify that the two are indeed paralleled with your ohm meter.
Tony
AD0VC
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Hard to tell, but a number of possibilities have been mentioned here. In addition to the obvious ones (maybe the other transistors failed open?), the driver IC could have failed, or the replacement transistors you got are floor sweepings
instead of first tier distribution.
Any time one transistor fails, the general recommendation has been to replace all four.
73, Willie N1JBJ
> On Sep 14, 2023, at 4:20 PM, Jerry <Jerryh47@...> wrote:
>
> I was more interested in responses to the main Question of my post ¡ª why should only Q9 be the failure multiple times??
