[Elecraft] K2 SSB, "Hi Cur" message on PTT

[Don Wilhelm]

Doug,

Start with the easy things first - it could be RF Feedback or some type 
of oscillation in the mic itself - or it could be a lack of carrier 
balance on the KSB2 board.  To check quickly, do not connect a 
microphone at all - just connect your paddles to the key jack, and in 
SSB mode, close the dot paddle (the DOT line inside the K2 is the same 
as PTT).  Do you have any power output?  You should not because there is 
no audio.  If you do have RF output, the first step is to adjust the 
carrier balance pot on the KSB2 board for minimum RF - you may have to 
compromise between LSB and USB, but the carrier level should drop to a 
very low level at the correct adjustment point.  That point should be 
near mid-range on the pot, if it is not, then look for a problem.
Once you have the carrier balanced, it is time to try the microphone 
again - since you now know the carrier balance is correct, this time 
suspect RF Feedback (or audio feedback if you have a computer soundcard 
also connected) if it happens when the mic is added.

There are other possibilities such as a problem in the ALC section of 
the KSB2 board, but try the above before doing anything else.

73,
Don W3FPR

Doug Heacock wrote:
> I dusted off my old K2 recently and decided to try to wire up an electret
> mic and give SSB a try--I've had the SSB module since I built the K2 years
> ago, but just never used it, because I had no mic at the time.  I've
> discovered that when I ground the PTT line with the K2 in LSB or USB mode, I
> get the "Hi Cur" message, and my output power goes to well over 15W,
> regardless of the setting of the power output control.
>
> I've done some of the voltage checks recommended in the SSB module manual,
> but only those for RX mode--I'm a little nervous about trying to measure
> voltages in transmit mode, because I don't know how long the PA can take
> that kind of current, and I don't want to fritz the final or cause other
> problems.  There are some voltage discrepancies associated with U2--pin 5 on
> that device is supposed to have 0.6v in RX mode, but I'm seeing more like
> 2.5v.  Pin 3 of U4--same story.
>
> If anyone out there has any suggestions for where to look for problems, or
> how to do further testing, I'm all ears.  I found an old thread in the list
> archives that suggested replacing Q3 and/or Q4 on the K2 control board, in
> case one of those 2N7000s happened to take a static electricity hit, but I
> haven't had a chance to do that yet (don't have any 7000s lying around), and
> I'm somewhat hesitant to go down that path because this rig seems to work
> just fine in CW mode.
>
> Many thanks, Doug
>   
>