[Elecraft] K2 meter alignment issue

[Don Wilhelm]

Mike,

That value for CAL S LO is way off.  And that indicates that something 
is not connected properly.  Look at the schematic for the Control Board 
in the lower left corner and check the values and soldering for all the 
components around U2 and Q12.  You also could have a problem with the 
connections (including the connectors) between the Control Board and the 
Front Panel RF Gain control.

I measured the voltages on a good working K2 - note that the AGC 
Threshold (U2 pin 5) was set to 3.74 volts instead of 3.8 volts which 
will make a little difference, but not a whole lot - the voltages should 
be proportional (or set your U2 pin 5 voltage to 3.74 before measuring).

With the RF Gain control set to full clockwise:
U2 pin 5 -- 3.74 volts
U2 pin 6 -- 3.74
U2 pin 7 -- 3.73
U2 pin 8 -- 8.34 (this voltage will depend on the output of the 8 volt 
regulator)
U2 pin 1 -- 3.74
U2 pin 2 -- 3.44
U2 pin 3 -- 3.42
U2 pin 4 -- 0.00

Q12 base -- 3.68
Emitter -----  3.42
Collector --   8.22

Then with the RF Gain set to full Counterclockwise:
U2 pin 5 -- 4.77 volts
U2 pin 6 -- 4.77
U2 pin 7 -- 4.76
U2 pin 8 -- 8.34 (this voltage will depend on the output of the 8 volt 
regulator)
U2 pin 1 -- 4.30
U2 pin 2 -- 4.30
U2 pin 3 -- 4.30
U2 pin 4 -- 0.00

Q12 base -- 4.58
Emitter -----  4.29
Collector --   8.22

If you find the voltages for U2 pins 5, 6, and 7 do not track my 
readings between full clockwise and full CCW, you can suspect a problem 
in the connection between the Control board RP6 resistors and the front 
panel RF Gain control.

OTOH, if the voltages for pins 5, 6, and 7 do track somewhat similar to 
mine, then the RF Gain is OK and the problem is with the components 
feeding U2A (pins 1, 2, and 3).

73,
Don W3FPR

On 5/30/2013 7:30 PM, VE3WDM wrote:
> Good evening Don, I checked the solder connections on Q12 and U2 all were
> good and I even reheated each connection allowing it to flow. I also checked
> for proper orientation for U2 and that's ok as well.
> D1 is good with band facing toward Q12 and to me that is the proper
> direction.
> As for CAL S LO the value at which the first bar goes out is 255 and comes
> back on at 000
> As for CAL S HI I am not able to get any of the bars on the meter to light
> up so I do not have a value for you.
> Thank very again for your time.
> Mike
> VE3WDM
>