[Elecraft] K2 weird problem

[Don Wilhelm]

Gregg,

If the power display does not indicate any output, it is quite possible that
VRFDET is being pulled down (which will cause the K2 to develop full power
output, and hence your Hi-Cur message).

Check the DC voltage on the ALC THR signal (on the KSB2 board U2 pin 5.
That should remain at a high level during CW transmit - I measure about 5.9
volts on a KSB2 here.  If ALC THR is at zero volts or close to it, Q1 would
conduct at the base/emitter junction and limit the voltage on VRFDET to
about 0.7 volts (or to 0.7 volts above the level of ALC THR).  I measure a
voltage of about 2.5 volts on the VRFDET line at a power output level of 5
watts.

If you do find ALC THR at a low level, that could be caused by either the
KSB2 firmware or the U2 chip itself.  Substitution for another KSB2 firmware
chip would be the quickest check to determine the culprit.

73,
Don W3FPR

> -----Original Message-----
>
> First I'd like to thank all of u guys fer pitching in to help me
> with this problem. That said, hereis an update. Power out set to
> 5w, CW mode. K2 works fine with no SSB brd intstalled. When SSB
> brd in,  on CW xmit, the bar graph reads no power, the power out
> at the ant reads abt 10 w, high current alarm comes on when
> xmitting.Problem is no longer intermittent, there all the time.
> Have replaced (new parts) Q1, Q2 , Q3 , D1, D2 ,D3, D5, es C36 on
> ssb brd. Appears to be somthing related to Q1, With Q1 remmoved,
> rig seems to xmit OK, Tryed removing D2, but that does not help.
> Haven't had my mic today so can't try Peter's suggestion  of
> measuring voltages while in ssb mode.Should I  be looking on
> another brd for somthing feeding the ALC circuitry ? i'm going to
> replace C19, C38, R4,es R9 on ssb brd tonight.
>        73  Gregg
>
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