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bitx v3 zero pa output

David Nelson
 

I have an bitx v3 with stock firmware. It was working fine with good output on all bands. Very good receive. I did not use it 
for a couple of weeks then when I started to use it again receive was fine but zero output. Thought it was my meter but I
tried some other meters with same results. Tried meter on another radio. Meter works fine. Tried listening on another
receiver and could hear myself very faintly. M y only test gear is a pretty good dmm. Replaced tr relay no change. Replaced
both irf510. Now when I key the mike instead of showing tx on display the display goes blank and I get a squeel. I do not know
if I have counterfiet 510 or I need to redo the bias adjustments. I found a test fixture on the net and built it. Both the old
510 and the new test good. I am retired heavy equipment mechanic at 82 yo and all I know about electronics is self taught.
Greatfull for any advice  anyone has for me.  Dave kc2ipx

Evan Hand
 

I had similar problem that I traced to rf feedback getting into the Nano controls.  That does not mean that it is your issue, just one other thing to test.  That fact that you changed the IRF510 is a potential pointer to the RF feedbackissue, as it is very lead and postion orientation.

Have you tried into a dummy load so that htere is minimal RF in the shack?  If you do not have the issue on the dummy load, then I would guess feedback is the issue.  If the problem still persists, then I would recheck the wiring and the solder joints on the devices that you replaced.

I would also use the DMM to measure the current to the PA (brown wire) and do the bias adjustments.

If all that fails to point you to the problem, then may need to build an RF probe to go with your DMM and trace the RF from TP2 through each TP until you get to the antenna output. (TP2 to TP7).  You should see a signal growing in strength from roughly 200mv PP to over 50v PP at the antenna.  Here is a link to scope traces of a version 5 (has the same power circuits) https://groups.io/g/BITX20/message/72786

73
Evan
AC9TU

David Nelson
 

Will try to work on this some more tomorrow. Thanks  Dave


On Wed, Nov 6, 2019 at 4:01 PM Evan Hand <elhandjr@...> wrote:

I had similar problem that I traced to rf feedback getting into the Nano controls.  That does not mean that it is your issue, just one other thing to test.  That fact that you changed the IRF510 is a potential pointer to the RF feedbackissue, as it is very lead and postion orientation.

Have you tried into a dummy load so that htere is minimal RF in the shack?  If you do not have the issue on the dummy load, then I would guess feedback is the issue.  If the problem still persists, then I would recheck the wiring and the solder joints on the devices that you replaced.

I would also use the DMM to measure the current to the PA (brown wire) and do the bias adjustments.

If all that fails to point you to the problem, then may need to build an RF probe to go with your DMM and trace the RF from TP2 through each TP until you get to the antenna output. (TP2 to TP7).  You should see a signal growing in strength from roughly 200mv PP to over 50v PP at the antenna.  Here is a link to scope traces of a version 5 (has the same power circuits) https://groups.io/g/BITX20/message/72786

73
Evan
AC9TU