[Elecraft] Dead K2

[Don Wilhelm]

Kristina,

You will just have to continue measuring things until you discover the 
root cause.  Did you measure the resistance at the power plug with the 
power switch ON?  Try the checks below (in order until you find the source).

Measure the resistance to ground from the cathode of D12.  You may find 
it quite low (indicating a short).  Remove the control board and check 
it again - if the resistance increases, look for the problem on the 
control board.

If not on the control board, remove the heat sink and then recheck - if 
things are OK with the heat sink removed, check the thermal pads.

If you still have not found it, the 'hunting' gets more difficult.  Use 
the schematic to follow the path of the 12V voltage line - it starts at 
the lower right corner of RF Board sheet 1, and goes to the regulators 
on the control board, and various places on the RF Board (mostly on 
sheet 4).  Check those paths thoroughly, even if it means removing some 
components to see which side of the component the short is located.
Remember that the most likely cause is a solder bridge (connecting 2 
points that should not connect together) so a VERY careful visual 
inspection may reveal the problem source.

Work in an orderly manner - a short on a power line is difficult to find 
because the PC traces seem to go everywhere and it is difficult to 
isolate them - expect some frustration in the process.

73,
Don W3FPR

Kristina Wright wrote:
> OK, here's what I've done so far: checked the resistance from the
> power plug to ground, the meter read infinite resistance. Also checked
> the voltage at the same and got 12 volts. Then I measured the voltage
> at the cathode end of D10 and got 12 volts with the power switch on
> and off, but at D12 I got nothing with the power off and 0.7 volts
> with it on. Obviously the fuse is being tripped, but I still don't see
> any shorts (yes I inspected the whole board carefully).
>  Thanks for the help so far, any more ideas?
> 
> 73,
> Kristina, KE7LUC