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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