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#sBitx Apparent short following unintended TX #sBitx

 

My from-kit sBitx (#131) now shorts every time turn on the power.

I received the kit last week and had it connect to my LDG AT-100 Pro II tuner. It was tuned for 80m. I had switched down to 40m and was listening LSB for a couple of hours. The mic was not connected, and, not finding how to set my call sign and grid within 10 minutes of searching, I typed "/callsign" on the cmd line and pressed <Enter>. At that point, I'm guessing the unit tried to transmit "/callsign" and immediately turned off. My power supply instantly went into "protect" mode as it did in ensuing attempts to power on the sBitx.?

Upon inspection of the mainboard, I found no visible indicator of where the short might be. Nothing appears blown or burned. The power cable has been checked and is fine. I have taken several detailed pics.

I am looking for a starting point for rectifying this problem. Does anyone have an idea of where my initial focus should be?
 

In all probability, one of the PA transistors is blown. Cut out the drain leads of the PA transistore and check if the short goes away.
- f

On Tue, Sep 13, 2022, 9:54 PM AB1ZU <ab1zu.00@...> wrote:
My from-kit sBitx (#131) now shorts every time turn on the power.

I received the kit last week and had it connect to my LDG AT-100 Pro II tuner. It was tuned for 80m. I had switched down to 40m and was listening LSB for a couple of hours. The mic was not connected, and, not finding how to set my call sign and grid within 10 minutes of searching, I typed "/callsign" on the cmd line and pressed <Enter>. At that point, I'm guessing the unit tried to transmit "/callsign" and immediately turned off. My power supply instantly went into "protect" mode as it did in ensuing attempts to power on the sBitx.?

Upon inspection of the mainboard, I found no visible indicator of where the short might be. Nothing appears blown or burned. The power cable has been checked and is fine. I have taken several detailed pics.

I am looking for a starting point for rectifying this problem. Does anyone have an idea of where my initial focus should be?
 

I ended up replacing both PA transistors and presumably will need to source more?IRFZ24Ns or equivalents for the future. The unit powered up without issue following replacing them.?

Now I'm on to dealing with the radio being off frequency and mostly deaf. I'm finding FT8 up 14kHz on 20m and 40m.

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