RE: K2/100 power maxes out

[Brian F. Wruble]

Don, that did it!  I got a 1N5711 and replaced D16.  It was easiest to mount
it on the bottom of the board.  That solved the problem.  Your diagnosis was
right on the button.

Thanks so very much for your time, wisdom and patience.

73 de Brian W3BW

-----Original Message-----
From: W3FPR - Don Wilhelm [mailto:[hidden email]]
Sent: Monday, September 05, 2005 3:22 PM
To: [hidden email]
Subject: RE: K2/100 power maxes out

Brian,

Sorry I forgot to mention subs on my last post - as a temporary sub, you can
use a 1N34 as the best choice, but a 1N914 or 1N4148 will work too - at
least enough to get you over the hump.  You should replace it with a 1N5711
when you are done because they have a bit more uniform response over the HF
range - your indicated power may be off a bit with the sub, but that is the
only consequence.

73,
Don W3FPR

> -----Original Message-----
> From: Brian F. Wruble [mailto:[hidden email]]
> Sent: Monday, September 05, 2005 3:46 PM
> To: [hidden email]
> Subject: RE: K2/100 power maxes out
>
>
> OK.  R26 shows only a bit over 2 volts, and not varying with
> power setting.
> I assume that D16 is the culprit.  T4 seems to be fine.  Unfortunately, I
> can't find any 1N5711s in my box.  Are there any acceptible substitutes?
> Otherwise, I'll order some and try again next weekend.
>
> Thanks again.  Brian
>
> -----Original Message-----
> From: W3FPR - Don Wilhelm [mailto:[hidden email]]
> Sent: Monday, September 05, 2005 1:11 PM
> To: [hidden email]
> Subject: RE: K2/100 power maxes out
>
> Brian,
>
> 0.5 volts is not enough voltage at those points - If your KPA100 is
> developing 100 watts (or the base K2 is developing 15 watts with the power
> set for <10 watts) the voltage should be about 4 volts during transmit.
>
> OK, so what we know is that the path is continuous and likely OK - next
> thing to do is check the diodes in the wattmeter circuit - they could have
> been zapped with a static discharge.  If you have 1N5711s in your bag of
> spare parts, I suggest that you arbitrarily replace them if there is any
> chance they could have been zapped.
>
> The other things that could cause low voltages in the wattmeter is T4 -
> there is really not that much else that could cause a complete failure to
> get a power level indication of some sort from the wattmeter.  Check that
> all the leads of T4 are well soldered (there are 6 leads and one
> is the red
> wire coming from the SO239 to terminal 5, and the other is the
> bare wire to
> terminal 6).
>
> BTW, D16 is the only diode that must work to provide power
> control - D17 is
> for the reflected power.  You may also have a bad connection to R26.
>
> One other thought that you may want to check for a voltage reading - the
> high end of R26 should show a substantial voltage (it does depend on the
> power output) if the forward power portion of the wattmeter is working -
> i.e. if diode D16 is OK and properly rectifying the output of T4.
>  Check the
> schematic and I believe you can follow the circuit.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> > From: Brian F. Wruble [mailto:[hidden email]]
> > Sent: Monday, September 05, 2005 11:27 AM
> > To: [hidden email]
> > Subject: RE: K2/100 power maxes out
> >
> >
> > OK.  I have about 0.5 volts at every one of those points.  U6 Pin
> > 8 is 4.9v
> > on both transmit and receive, which I assume is ok.  I have
> continuity on
> > pin 10 of the ribbon cable.  On the control board, I have 1 volt
> > at C11 and
> > also at U6 pin 2 during transmit.  So, it appears that the V
> > RFDET signal is
> > getting to the control board.  What do think I should try now?
> >
> > de Brian
> >
> > -----Original Message-----
> > From: W3FPR - Don Wilhelm [mailto:[hidden email]]
> > Sent: Monday, September 05, 2005 9:49 AM
> > To: [hidden email]
> > Subject: RE: K2/100 power maxes out
> >
> > Brian,
> >
> > Sorry for the confusion, look at the KPA100 for those points -
> the KPA100
> > wattmeter or the circuits that pass the wattmeter output to the
> > base K2 are
> > likely the culprit.  On the KPA100 schematic they are located
> in the upper
> > right corner of the 1st sheet.
> >
> > 73,
> > Don W3FPR
> >
> > > -----Original Message-----
> > > From: Brian F. Wruble [mailto:[hidden email]]
> > > Sent: Monday, September 05, 2005 10:31 AM
> > > To: [hidden email]
> > > Subject: RE: [Elecraft] K2/100 power maxes out
> > >
> > >
> > > Don, I'm confused, and feeling a little dumb.  I spent the last
> > hour going
> > > over the schematics, and can't seem to figure out where these
> > points are.
> > > U5 on the RF board has pin 5 as a ground.
> > >
> > > Is the U6 you refer to the MCU on the Control Board?  Or is it
> > > the U6 in the
> > > PLL Synthesizer area of the RF board?
> > >
> > >
> > > Where is the wattmeter calibration pot?
> > >
> > > Tnx in advance.  73, Brian W3BW
> > >
> > > -----Original Message-----
> > > From: W3FPR - Don Wilhelm [mailto:[hidden email]]
> > > Sent: Sunday, September 04, 2005 9:59 PM
> > > To: [hidden email]; [hidden email]
> > > Subject: RE: [Elecraft] K2/100 power maxes out
> > >
> > > Brian,
> > >
> > > If I understand your wording correctly, no matter whhere you
> > set the power
> > > level <10 watts, the K2 output is 14 to 15 watts, and if the
> > > power level is
> > > set for >10 watts the output is 100 watts (or more).  (Should I have
> > > misunderstood, ignore the rest.)
> > >
> > > The normal cause of that behavior is some failure in the
> > > wattmeter circuit -
> > > and the net result is that the VRFDET signal to the
> > > microprocessor indicates
> > > no power is being transmitted, so the K2 firmware responds by
> increasing
> > > power in an attempt to obtain 'sufficient' output - yes, it really is
> > > sufficient, but the microprocessor is not getting the signal to
> > > tell it so.
> > >
> > > To find out where the failed component is, turn the power to
> > less than 10
> > > watts, connect a dummy load.  Then transmit for brief periods while
> > > monitoring voltage at the following points (you are looking for
> > > the presence
> > > of a 'healthy' voltage, and not a specific voltage - you only
> > need to find
> > > where the path is broken).
> > > U5 pin 5   -- voltage direct from the wattmeter calibration pot
> > > U5 pin 7  -- buffer output
> > > U6 pin 3  -- VRFDET driver input
> > > U6 pin 6  -- VRFDET driver output
> > >
> > > If you have a voltage at U6 pin 3, but not at pin 6, then check
> > > the voltage
> > > at U6 pin 8 - it should be about 5 volts during transmit.
> > >
> > > If all is well at the points above, the problem is with the
> > > VRFDET signal on
> > > the K2 control board, or possibly a break in the 10 conductor
> > ribbon cable
> > > (pin 10)
> > >
> > > BTW, if you have the KPA100 in a separate enclosure, you may
> > want to check
> > > the cable that goes from the KIO2 to the KPA100 for
> continuity on pin 7.
> > >
> > > 73,
> > > Don W3FPR
> > >
> > > > -----Original Message-----
> > >
> > > >
> > > > Hi all:  I got no response, so I thought I'd try to be a little
> > > > clearer.  My
> > > > K2 was working fb, in all regards.  Suddenly, it maxes out at
> > > about 14-15
> > > > watts, regardless of the power setting.  With power set >10
> > > watts, kicking
> > > > in the amp, this naturally leads to output of 100 watts, regardless.
> > > >
> > > > I did a complete reset, but the symptoms remain the same.
> Can anyone
> > > > suggest a starting point to trouble shoot?  Tnx de Brian W3BW
> > > >
> > > >
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> Date: 9/2/2005
> > >
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