[Elecraft] K2 voltage on SCLK line and degraded receiver performance at test 2

[Wendell Pyles]

I have completed the K2 down to Test 2, at which time the receiver is
supposed to work on 40 meters.   All parts, values, etc of Test 2 were
completed successfully down to I.F. Amplifier Alignment on page 61.  I
do hear faint to medium faint cw and foreign broadcast there; all
filters (1-4) sound different, but am not pleased with the strength of
the signals.  I noticed that when I place my fingers on the PC board
under L1 & L2, the signals are quite a bit stronger, although somewhat
raspy (distorted) .  I proceeded to check current and voltage under the
display key and have 13.1 V and .220 amps.   The power supply is well
regulated, a 35 amp Astron which is used successfully to power other
transceivers at this station.  Upon checking some of the voltages, I
note that I have 5.07 V on the 5 volt regulator, and 8.37V on the 8 volt
regulator, all healthy voltages.   I did note however, that pin 7 of the
U4 on the RF board was 5.07 V, not the 0.0V as suggested by the chart on
page 17 of the Appendix E.   I note this is SCK which I take to be
System Clock pulse.  The same line on U5 also shows 5.07 V (same buss).
While looking for solder bridges, (even to the point of removing U4 and
U5 from the RF board)  I found that the cause of the 5.07 V on U4-7 and
U5-1 seems to be due to the fact that this line is  sourced from the
microprocessor on the control board. In other words the voltage remained
on those two pin pads.  When I removed the U6 on the control board, the
5 volts went away. Is it supposed to show 5 volts instead of zero, and
the table is a mistake??  I don't see how the processor  functions,
controlling all features I have tried successfully?
On trying to fix the low signal receive, I bypassed the T-R switch by
running a cap from W1 to W6, and even from the antenna center conductor
to W1 or W6, but no appreciable change in signal strength.  Only a raspy
sound.

I would be happy to have any suggestions you might be able to offer.


Wendell

WA4ERD