[Elecraft] K2 Control Board Issue

[Don Wilhelm]

Glenn,

R7 has no association with the voltage display - it does however have a 
lot to do with the current display.

The voltage detection is done by the voltage divider consisting of R9 
and R10 on the control board.  The voltage measured at the junction of 
R9 and R10 (or U3 pin 5) should be 20% of the 12 volt input (as measured 
at P7 pin 2).

I would wager you have a bad solder connection at R10.  Measure the 
resistance from U3 pin 5 to ground - it should read 196k.

As for R7 reading zero ohms, I would suggest you look for a solder 
bridge.  If you find none, then remove U6 and remeasure.  Should the R7 
resistance come up to normal, then U6 will have to be replaced - and be 
careful about taking proper anti-static measures.

Is there any chance you are using an old VOM or VTVM to check 
resistances?  If so, know that those can cause solid state devices to 
conduct and may even cause damage.  Use a DMM - those do not use high 
voltages for resistance measurements.

73,
Don W3FPR

On 5/9/2014 1:14 PM, Glenn Haffly wrote:
> Doing something I should have not done , I managed to blow up Q11on the
> control board. I fixed that with a replacement from my junkbox. All
> voltages are correct on control board U3. When tapping display I get a
> voltage of 23.3 volts indicated from a 12 volt supply and zero current.
> Further checking shows R7 on the control board is zero ohms instead of
> 1.78K. How important is it to replace R7
> with a 1% resistor rather than something from the junkbox?
> Everything else on the K2 works fine , TX and RX are OK.
> Hopefully a replacement R7 will then display the correct voltage and
> current.
> Any input from the reflector is appreciated.
>