K2 weird problem

[Gregg mulder]

Hello agn fellow Elecrafters,
  I still have a problem with my K2, upon cold startup. power cont. set to 5w. CW mode. when 1st x-mit . bargraph shows almost no ind. but hi curent alarm, power out is 10+ watts( 40m) es after a minite or 2 all is backto normal with bar graph showing 5w es power out is 5w es no alarm. i followed Keith Darwins suggestion es made some rework eliminators. I narrowed the problem to when the ssb brd is plugged in. with ssb brd out, all is fine. I went thru a rebuild of the ssb board es all parts are in proper places es no cold solder joint or bridges. Problem is with ssb brd. could my problem be a faulty (intermittent) IC ??? Any sugestions appreciated.      tnx,   Gregg WB8LZG
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[Don Wilhelm-3]

Gregg,

There are no ICs on the KSB2 board that should cause a problem of that
nature.
When in CW mode, and during transmit, the only components that should be in
the signal path electrically are C42, D3, Q3 and C39.

Follow along on the KSB2 schematic - at the bottom, the BFO signal enters at
P1 pin 12, goes through C42, then D3 should be conducting because the TXC
signal from the KSB2 firmware should be active (+5v) during CW transmit.
The TXC signal also causes Q3 to conduct and the BFO signal flows out the
emitter of Q1 and through C39 to pin 7 of P1 - from there it goes to the RF
Board and on to the transmit mixer.  Be certain the TXC signal is correctly
present from the firmware chip (Pin 12 of U1).

So there is little involved on the KSB2 board for CW transmit.  Check to see
if you have the proper conditions present for the signal flow described
above, and that information should lead you to the source of the problem.
Check Q3, D3, and possibly D5.

73,
Don W3FPR

> -----Original Message-----
>
> Hello agn fellow Elecrafters,
>   I still have a problem with my K2, upon cold startup. power
> cont. set to 5w. CW mode. when 1st x-mit . bargraph shows almost
> no ind. but hi curent alarm, power out is 10+ watts( 40m) es
> after a minite or 2 all is backto normal with bar graph showing
> 5w es power out is 5w es no alarm. i followed Keith Darwins
> suggestion es made some rework eliminators. I narrowed the
> problem to when the ssb brd is plugged in. with ssb brd out, all
> is fine. I went thru a rebuild of the ssb board es all parts are
> in proper places es no cold solder joint or bridges. Problem is
> with ssb brd. could my problem be a faulty (intermittent) IC ???
> Any sugestions appreciated.      tnx,   Gregg WB8LZG
> _______________________________________________
>

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[w9cf]

Others on the list know infinitely more than I do about how the K2-KSB2
work, but from the symptoms, I would guess that the KSB2 is loading down
the VRFDET line so that the K2 thinks it isn't generating enough power.
It then tries to up the power, gives the high current warning, and drops
back to 10 watts.  This would suggest checking the components around Q1
on the KSB2.

73 Kevin w9cf

>
> Hello agn fellow Elecrafters,
>   I still have a problem with my K2, upon cold startup. power
> cont. set to 5w. CW mode. when 1st x-mit . bargraph shows almost
> no ind. but hi curent alarm, power out is 10+ watts( 40m) es
> after a minite or 2 all is backto normal with bar graph showing
> 5w es power out is 5w es no alarm. i followed Keith Darwins
> suggestion es made some rework eliminators. I narrowed the
> problem to when the ssb brd is plugged in. with ssb brd out, all
> is fine. I went thru a rebuild of the ssb board es all parts are
> in proper places es no cold solder joint or bridges. Problem is
> with ssb brd. could my problem be a faulty (intermittent) IC ???
> Any sugestions appreciated.      tnx,   Gregg WB8LZG

=-------------------------------------------------------------
Kevin Schmidt, [hidden email], http://fermi.la.asu.edu/w9cf
Department of Physics
Arizona State University, Tempe, AZ 85287-1504
[phone] Fax: [phone]
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[Peter Zenker]

 I just had a very similar problem at a customers K2: Without SSB board but
jumpers and C167 set, all is ok. With build in SSB board ALC sometimes
worked, sometimes not.

The failure was caused by a reversed Diode D2. Even if your Diode is not
reversed, it may have a thermal failure. Also check transistor Q1


73 de Peter, DL2FI

> -----Ursprüngliche Nachricht-----
> Von: [hidden email]
> [mailto:[hidden email]] Im Auftrag von Kevin Schmidt
> Gesendet: Dienstag, 28. November 2006 19:10
> An: [hidden email]
> Betreff: RE: [Elecraft] K2 weird problem
>
> Others on the list know infinitely more than I do about how
> the K2-KSB2 work, but from the symptoms, I would guess that
> the KSB2 is loading down the VRFDET line so that the K2
> thinks it isn't generating enough power.
> It then tries to up the power, gives the high current
> warning, and drops back to 10 watts.  This would suggest
> checking the components around Q1 on the KSB2.
>
> 73 Kevin w9cf
>
> >
> > Hello agn fellow Elecrafters,
> >   I still have a problem with my K2, upon cold startup. power cont.
> > set to 5w. CW mode. when 1st x-mit . bargraph shows almost
> no ind. but
> > hi curent alarm, power out is 10+ watts( 40m) es after a
> minite or 2
> > all is backto normal with bar graph showing 5w es power out
> is 5w es
> > no alarm. i followed Keith Darwins suggestion es made some rework
> > eliminators. I narrowed the problem to when the ssb brd is
> plugged in.
> > with ssb brd out, all is fine. I went thru a rebuild of the
> ssb board
> > es all parts are in proper places es no cold solder joint
> or bridges.
> > Problem is with ssb brd. could my problem be a faulty
> (intermittent)
> > IC ???
> > Any sugestions appreciated.      tnx,   Gregg WB8LZG
>
> =-------------------------------------------------------------
> Kevin Schmidt, [hidden email],
> http://fermi.la.asu.edu/w9cf Department of Physics Arizona
> State University, Tempe, AZ 85287-1504
> [phone] Fax: [phone]
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>

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