[Elecraft] Dead K2 After nearby power surge

[Don Wilhelm]

Fred,

Zero volts on both is way better than 8 volts on both - at least the K2 
is not trying to transmit.

Check the gates of Q3 and Q4 on the control board.  The gate of Q4 
should be at 5 volts and the gate of Q3 should be near zero.  If that is 
true (and only if that is true), short the drain of Q4 to its source and 
see if the 8R voltage rail comes to life - 8 volts at the anode of D6.
If so, replace Q4.  If still no 8 volts on 8R, then something is wrong 
with Q2 (likely open).
OTOH, if the gates of both Q3 and Q4 are near zero volts, you have a bad 
microprocessor output.

73,
Don W3FPR

PS: Top posting is preferred here, it is easier to see the latest 
without scrolling all the way to the bottom - on some posts it is hard 
to determine what has been added - I know about 'netiquette', but that 
is slow and laborious.

KC9QQ wrote:
>
> Don Wilhelm-4 wrote:
>   
>> Fred,
>>
>> In cases like yours, first step is to connect a dummy load to the K2 
>> just in case it is trying to transmit - it is not good to enter transmit 
>> state without a load on the PA transistors.  If it is a K2/100, remove 
>> the KPA100 and connect the dummy load to the BNC antenna jack on the 
>> lower rear panel.
>>
>> First thing is to check the state of the 8T and 8R voltage rails. Those 
>> are easily checked at the anodes of D6 and D7.  If D7 anode has 8 volts 
>> on it while D6 anode has zero volts, then the K2 is in a transmit 
>> state.  If both D7 and D6 anodes have 8 volts present, power it only 
>> briefly while making further checks lest some components overheat.
>>
>> If both 8T and 8R are present, you need to check the state of the RX 
>> signal at the gate of control board Q4 as well as the TX signal at the 
>> gate of CB Q3 - one should be on (about 5 volts) while the other should 
>> be off (near zero volts).  If both of these are on, the microprocessor 
>> was zapped with the power surge, but if only one is on, the problem is a 
>> shorted Q3 or Q4 on the control board.
>>
>> 73,
>> Don W3FPR
>>
>> Fred Keller wrote:
>>     
>>> I also just noticed that the power output transistors Q7 and Q8 are 
>>> getting warm when the power is on.  I did not say  before but, their 
>>> is no display or any other activity on the control board or front panel.
>>>
>>> Fred, KC9QQ
>>>
>>>       
> Don,
>
> I pulled the control board again to reset the relays and then reinstalled it
> to make the measurements on D6 and D7.  When I powered the unit, Elecraft
> was again shown and the frequency of 7100 was briefly displayed.  When then
> display went out I measured the anodes and cathodes of both d6 and d7 and
> measured nearly zero volts on both.
>
> Fred
>
>   
>