Re: Which xmit transistor is blown?

 

Sean,

Occasionally I get power drop and fluctuation and I found it was the power connector. 1-2A is a lot for the
pin contact.. pull the power plug from the board and put it back a couple of times and see..

Raj

At 01/09/2018, you wrote:
I have had periodic issues with the ubitx that led me to believe that my finals (IRF510) were blown, and the radio seemed to work as expected after replacement, so perhaps they were.

I have a question though...is there a good way to tell what has gone out in the xmit power chain? I recently replaced Q90 with an mmbt2222a (smt version of the 2n2222a), and then the next two stages with 2n2222a's (in TO-18 form). No other changes to the radio.

It worked fine for a few days, though the 2n2222a's would get hot to the touch in digital mode transmit (which I think is to be expected). Today I started to experience 'bouncing' power readings during transmit (as shown in the meter on my tuner) before the radio simply stopped putting out much power at all. Nothing feels hot...and nothing looks burned or heat stressed to the naked eye.

So...before I start replacing things, I wanted to ask how to diagnose the problem. Is it most likely that I cooked some transistors, and how do I best till which ones?

73

Sean

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