[Elecraft] K2: 8A Control Resistance 2.72 to 3.50 depending on R1

[David Woolley]

David Woolley wrote:
> 
> I've  assembled the control board (and most of the front panel.  In 
> doing the control board resistance checks I've got an apparently out of 
> range value for the 8A value.  With R1 at the low resistance end of the 
> track, it is 2k72, which is below the minimum of 3k0, in the manual. 
> With R1 at the high resistance limit, it is 3k5.  Do I have a problem? 

I *did* have a problem that was indicated by this; even though I thought 
I had carefully checked, I mixed up the 5 and 8 volt regulators.  I've 
switched them over now, and apart from losing some of the through hole 
plating, it seems OK, with a couple of minor reservations.

In the hope that it will help someone searching in the future, the 
symptoms, on powering up, were:

- All the segments on the display showed to some extent from all
   angles and dominated the proper display when viewed from above
   the horizontal.

- When the power supply voltage was above, approximately, the 8V
   regulator drop out, it kept sensing slight changes in the pots,
   so the display kept going to various parameter mode change displays.

- The current draw, measured externally, was around 220mA.

- Nothing on the control board seemed to be running warm, but there
   were indications that something on the front panel, near the centre,
   was, although not really hot.

- The internal voltmeter, was showing about 5V when the external supply
   was turned down (I presume this is because it was using the the
   nominal 5V as the reference, which was actually just was close to
   the supply voltage, as the 8V regulator in the 5V supply had dropped
   out.

- No segments lit on the bargraph.

The slight reservations are that the AGC threshold calibration voltage 
only reaches 3.79, with R1 on the end stop and the current sense test 
showed 0.14 amps (0.08 to 0.22) difference most of the time, with the 
odd excursion to 0.16, compared with the manual figures of 0.16 to 0.18.

-- 
David Woolley
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