[Elecraft] KX1 Please need help with T/R thump

[Jerry W7ANM]

Don,

Installed the 2n3904 for Q7. Transmit voltage now normal 0.65V going to zero
when switched to receive. 6T_2 voltage at R28 still 5.63v for TX and 0v at
RX.  Unfortunately thump still there unchanged.....

Jerry


"Jerry,

Those voltages do look better.  Did the thump change any at all?
I would suggest you look for an incorrect value component somewhere in
muting transistor area.
Is there any chance that you mounted the muting transistors upside-down?  I
have seen that, and yes it causes a thump.  The flat side of the transistors
should face away from the board.

73,
Don W3FPR"  


Don,

Thump is the same. It does not seemed to have changed any. If anything the
T-R turn around is snappier is all (.047 cap across c9 has been removed).
Thump has same intensity and duration.

I have checked the muting transistors and they are not installed upside
down. The other components associated with the muting transistors are the
correct ones. In fact I swapped out c9 just in case it might have been
open.... No improvement.....

73,
Jerry


"Jerry,

OK, but I have run out of ideas.  All I can say is that it is abnormal - a
properly operating KX1 does not do that.

Are you operating into a dummy load or an antenna?  If that is into an
antenna, try a dummy load.  You could have some form of RF feedback from an
antenna, and the results of that condition are unpredictable - but the place
to fix that situation is in the antenna system.

73,
Don W3FPR"


Don,

It is the same with an antenna or dummy load.

What would be the effect of a slow or strange MCU Mute signal? Anything to
look at with a scope?

Is a normal KX1 thumpy to any degree?


Jerry


"Jerry,

I would not say the KX1 is "thumpy", but the sidetone note is not the
cleanest shape in the world.
Can you determine whether it is the return to receive that creates the thump
or is it something on the tail end of the sidetone?  You might try turning
the STL parameter down as low as it can go for a test.  Several that have
come into me for repair have the sidetone cranked up to max and they really
sound terrible.

73,
Don W3FPR"


Hi Don,

It is definitely the return to receive that creates the thump. The way I
determined that is to set the Menu T-R to something really long like 400 or
500 or so. Also I can set the STL to 0 or 1 (or even 2 or 3). Then with
these parameters you can key the KX1 and you would hear the side tone very
much separated from the change-over from T to R and the thump.

The sidetone sounds good. Not distorted or strange but, as above, after you
have stopped keying the sidetone, when the Menu T-R times out , you hear the
thump. I always run the sidetone at 1 or 2 normally. You can hear this with
an antenna or a dummy load connected, using batteries or power supply, any
STL, and using any headphones.

Please try this on one of your KX1s and let me know what you hear in your
normal one.

Oh, I did do some more voltage checks this am. Q2  and Q3 voltages are in
spec. U1s mute line is the proper voltage also.

73,
Jerry



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