[Elecraft] [K2] Update: K2/100 loss of power control (long post)

[david]

New diodes arrived yesterday, thanks to Richard at Elecraft.  After
installation and re-calibration of the SWR/wattmeter, everything looks
good, I made two quick contacts on 20m PSK31, one in Greece, the other
in Slovak Republic.

Thanks again Don, Richard, and Elecraft!

73,  David AJ4TF


On Sat, 2011-06-11 at 19:48 -0400, david wrote:
> Don,
> 
> Thanks for confirming my diagnosis.  I *usually* remember to disconnect
> the antenna when I am not operating.
> 
> I assume that the standard 1N5711 will work, Elecraft doesn't screen
> them for any special characteristics do they?
> 
> As always, I'm sure I'm not the only one that appreciates the knowledge
> you bring to the Elecraft community.
> 
> David AJ4TF
> 
> 
> On Sat, 2011-06-11 at 18:13 -0400, Don Wilhelm wrote:
> > David,
> > 
> > Yes, it looks like U5, U6, Q10, Q11 and the associated components are 
> > behaving as they should.
> > 
> > It certainly could be that D16 and D17 are not either open or shorted, 
> > but are not fully functioning as they should.  The fact that you could 
> > only get the resistance measured at the wiper of R26 as high as 30k does 
> > confirm that -- replace the diodes.
> > 
> > It also seems from your description that things are a bit intermittent 
> > and erratic, so while you are in there to replace the diodes, give the 
> > soldering in the wattmeter area (particularly T4) a good inspection and 
> > perhaps re-flow the solder with a hot iron (800 degF for the KPA100 
> > board), and perhaps add a tiny bit of new solder (actually you are 
> > adding a bit of flux).
> > 
> > Yes, those diodes are sensitive to lightning surges.  Switch the K2 
> > antenna to a dummy load when not in use for best results.
> > 
> > 73,
> > Don W3FPR
> > 
> > On 6/11/2011 4:42 PM, david wrote:
> > > K2/100 s/n 7006
> > > Initial symptom:  No control of output power at any knob setting.  At
> > > 1-9W setting, output was>10W as measured by external wattmeter, SWR
> > > read back>9.9 (external meter shows around 1:1).  At 10-100W setting,
> > > output>100W, SWR>9.9.  HI REFL message displayed.
> > >
> > > Unit was previously working fine for several months.
> > >