[Elecraft] K2 Troubleshooting

[Don Wilhelm]

Ron,

Is this a newly built K2 that has not worked before, or has it once 
worked and has now failed?

The DC voltage chart listings for the Control Board are for the 
condition that the Front Panel is removed. If you have the Front Panel 
plugged in, the U2 voltages will be quited different.
I assume you are referring to Control Board U2 pins 1, 2, and 3 rather 
than pins 5, 6, and 7. With the Front panel in place and the RF Gain at 
maximum, U2 pin 5 should be set using the AGC Threshold control to 3.8 
volts - check that first. If you are unable to achieve 3.8 volts, then 
check the voltage of the 8 volt regulator and set the U2 pin 5 voltage 
to 47% of the regulator output (but not less than 3.65 volts).

Back up a bit and make some other checks.
1) Check out the 'stupid' things first - did you remove the KDSP2 or 
KAF2 from the Control Board? That will cause no audio. Did you remove 
the KSB2 and fail to insert the jumpers? Did you remove the KNB2 and not 
replace the jumper? Do you have either the K60XV option or the K160RX 
option not plugged in? Each of these options will stop receive if 
removed and the appropriate jumpers are not installed. Do you have the 
K160RX installed and RANT turned on for the band in question?
2) If you are receiving a signal of any kind, does the S-meter move? 
Tune around the bands with the preamp on and see if anything gives an 
s-meter indication.
3) Tap on RF board W3 with a screwdriver tip while the AF gain is set to 
max - do you hear a click when you do that? If you do, then the IF 
amplifier, product detector and the AF Amp on the Control Board have a 
path capable of passing the signal.
4) If no sound is heard during the test above, try tapping on U11 pin 1 
with the screwdriver tip (be careful not to short to other pins). If you 
hear clicks, then the product detector is working.
5) No clicks above, try U11 pin 4 (using the same caution). If you hear 
clicks, the audio stages are good.
6) If you have gotten this far and still hear nothing, check the /Mute 
signal voltage at Control Board U6 pin 17 - if it is near zero, the 
microprocessor is muting the audio. In receive, this signal will be near 
5 volts.

If you have not found the problem source by these steps, let us know and 
we will try to help more.

73,
Don W3FPR



Ron McCurdy wrote:
>
> My reason for troubleshooting is there is NO SOUND. I can hear the 
> sidetone when I turn it on. I cannot hear the 7000hz tone.
>
> 1. My reference oscillator output is 0.511…a little low.
>
> 2. VCO output is okay.
>
> 3. BFO output is okay.
>
> 4. Mixer, I.F. amplifier, & Crystal filter = 0.00 vdc.
>
> So, I started with the control board. U1 voltages are okay. U3 
> voltages are okay. U4 is a little low at 7.80 vdc. U5 is perfect. 
> U6-U10 are okay. The problems:
>
> 1. U2 voltages are around 3.27 vdc instead of 6.9 vdc input voltage is 
> 7.80 on pin 8.
>
> I didn’t want to move on to the RF board without finding the problem 
> with the Control Board. Do you have any suggestions for finding where 
> the U2 voltages are dropping off.
>
> When I adjusted the AGC in step 5 page 48, I was only able to get 3.71 
> vdc.
>
> Ron, KE5QDA
>
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