[Elecraft] K2 Failure

[Don Wilhelm]

Ted,

Matt is correct, if you measure 0 volts on *both* sides of F1, then the 
power source and D10 are suspect.
It could be that the 0 volts is the result of your power source folding 
back or the soldering of D10 or the soldering of the power jack.

In any case, cure the low resistance at the collectors of Q7/Q8 first - 
that low resistance indicates a direct short for the 12 volt power input.
Once that is solved, you can move on to other potential problems.

DO NOT attempt a TUNE or Transmit with the heat sink removed - doing 
that will kill the PA transistors very quickly.

73,
Don W3FPR

On 12/4/2015 11:36 PM, Matt Maguire wrote:
> Good move taking a rest and a glass of wine — it is important not to panic, as that can lead to doing something silly :)
>
> If you were entering 10000, you would have been tapping the « 0 » key next the the VFO knob multiple times, and maybe the pressure has caused the front panel and control boards to come into contact and short out. As I remember, there was not a lot of clearance there, especially with the adapter board for the encoder. I’d be looking for possible shorts around there.
>
> Just a comment on your observations with F1 — if you are applying power and measure 0V on both sides of F1, then that suggests that F1 is not open circuit. It may indicate that diode D10 has gone high resistance and is dropping the 13.8V when the radio tries to draw current.
>   
> -- 
> 73 de Matt VK2RQ
>
> On 5 décembre 2015 at 2:56:47 PM, Dauer, Edward (edauer at law.du.edu) wrote:
>
> More on the defunct K2: I measured the DC voltage on both sides of F1,
> the self-resetting fuse. With the power switch “off” the voltage is 13.8.
> With it on, the voltage is essentially zero on both sides of F1.
> Measured the resistance to ground at the collector of Q7 - it’s about 2
> ohms, not the >500 it should be. But that doesn’t mean that Q7 or Q8 is
> the culprit. A short anywhere on the DC line could cause that reading
> anywhere else, yes? So, what’s the best procedure to isolate the problem
> — I removed the KNB2 and the KAF2; no change. Tomorrow, in the cold gray
> light of dawn, I will pull the front panel board and the control board off
> the RF board, to see if that narrows it down. Tonight, I will just have
> another glass of wine. That should help.
>
> Anyone know if F1 has a reset time of just under a second? If so, then
> the “popping” noise may be F1 trying to reset itself. Which doesn’t help
> locate the downstream problem, of course. But it would strongly suggest a
> DC short somewhere rather than some configuration glitch, yes?
>
> Ted, KN1CBR
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