[Elecraft] K2 Power Fluctations

[Randy Foltz]

I have K2 serial nr 213.  It has been updated to Rev B.  Modules are KAT2, 
KIO2, KAF2, K160RX, and KNB2.  About everything but the SSB and DSP modules.

Thursday night I noticed that the power was fluctuating more than the usual 
1 bar.  It would go from 5 w up to 7 w then down to 2 w and sometimes below 
1 w.  Turning the Power knob always got it back to 5, but it would soon, 30 
seconds or less, start to vary again.  Similar things happened when I hooked 
up to a dummy load.  ANT1 or ANT2 and different coax jumpers made no 
difference.  This tells me it isn't the antenna, the coax, or the ANT1 or 2 
jacks.

Today, Friday, I changed R98 to 1k.  Again the power jumped as it had on 
Thursday.  This time I did a bit more testing into the dummy load.  With the 
ATU set to CALP and the Power set to 5.0 I recorded the power out reading 
every 5 seconds for 30 seconds after pressing the TUNE.  After leaving the 
K2 off for 30 seconds I repeated the readings.  They are shown below.

Immediate  5sec  10sec  15sec  20sec   25sec   30sec
0.1        4.4   4.8    4.7    4.7     4.7     5.0
0.1        4.4   4.6    4.7    4.9     3.9     3.7
0.1        3.4   3.5    3.6    3.6     3.7     4.0
0.1        1.3   1.7    1.4    1.6     1.4     4.0
0.1        5.0   5.1    5.2    5.7     3.8     3.8
0.1        4.3   4.0    4.8    5.5     5.3     4.6
0.1        5.0   5.0    5.2    5.1     5.3     5.2

Only 2 of these 7 sets are within the +/- 0.5W spec.

I then let it set for 5 minutes and took the following readings

Immediate  5sec  10sec  15sec  20sec   25sec   30sec
0.1        5.1   4.8    4.7    5.1     5.2     5.1
0.1        5.1   5.1    5.2    5.1     5.2     3.3
0.1        4.3   4.2    4.2    4.2     4.2     4.4
0.1        4.6   4.8    4.9    5.1     5.3     5.3
0.1        4.7   5.0    4.1    4.2     4.0     4.0
0.1        5.7   5.5    5.7    5.7     5.7     5.9
0.1        5.4   5.5    5.5    4.9     5.6     5.7

Again only 2 of the 7 sets are within the +/- 0.5W spec.

After each 30 second set of readings the heat sink was warm to the touch, 
but not hot.  The power supply was a 20 A Astron.

Suggestions of what to look at would be welcome.

Randy, K7TQ