K2 NO AF output

[g0who]

My K2 has no AF output, not even hiss.

I suspected mute circuit but voltages on Q6 & Q7 Source 4.8v, gate 1.1v and drain 4.8v, though low for gate may be within tolerance.
There is 0v on all three of vols 1,2 & 3 at pins 1,2 & 3 of P1. Where should this voltage come from?
The only visible change I note is R97 on the RF board which shows signs of having overheated at some time, though colour banding still clear and measures 32 ohms. (Maybe during initial construction/alignment?)

Possibly quite separate: when I key K2 on CW (listening on separate RX) display shows frequency shift of 22kHz and audio brief chirp signal only.

Advice sought on where to check next
Robert (g0who)


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[Don Wilhelm-4]

Robert,

You are not likely to find any measurable voltage on VOL1, VOL2 or
VOL3.  This will be a low level audio signal, so unless you have a
sensitive oscilloscope, you are likely to see zero or quite close to
that (note that the DC voltage table says .02 volts, but with an "*" on
it).  Any DC voltage would be the residual from the input of the LM380 IC.

You frequency shift may be related, and in fact, if it is as much as 22
kHz, that is not a good indication.
Check the frequencies of the oscillators and TP1 and TP2 using the
internal counter probe and CAL FCTR.  TP2 is the BFO signal and should
be near 4915 kHz - TP1 is the VFO frequency and when tuned to a lower
band edge should have a frequency near that indicated in the Schematic
Key page near the back of the manual.  If those frequencies are
substantially different than the normal values, your receive signal may
be getting absorbed in the bandpass filters because the actual received
frequency is out of range.  Make certain the oscillators are correct
first, then pursue other problems.

The best way to troubleshoot a receive problem is to use a strong signal
oscillator and an RF Probe (like the ones shown in the manual Appendix
E) to inject a strong signal into the front end of the receiver and
follow it according to the steps in Receive Signal Tracing.

73,
Don W3FPR


73,
Don W3FPR

Robert Clutson wrote:

> My K2 has no AF output, not even hiss.
>
> I suspected mute circuit but voltages on Q6 & Q7 Source 4.8v, gate 1.1v and drain 4.8v, though low for gate may be within tolerance.
> There is 0v on all three of vols 1,2 & 3 at pins 1,2 & 3 of P1. Where should this voltage come from?
> The only visible change I note is R97 on the RF board which shows signs of having overheated at some time, though colour banding still clear and measures 32 ohms. (Maybe during initial construction/alignment?)
>
> Possibly quite separate: when I key K2 on CW (listening on separate RX) display shows frequency shift of 22kHz and audio brief chirp signal only.
>
> Advice sought on where to check next
> Robert (g0who)
>
>
>  
> ------------------------------------------------------------------------
>
>
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>  

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