K2 alignment and test, part III problem

[William Schmidt]

I just finished up the RF board and am proceeding to the testing.  Much to my dismay, however, I got no power output when I tried to
adjust the 40 m BPF.  I'm getting 13.5 v to all of the collectors and I pull 220 ma on receive and 420 ma on tune.
The RF detector resistors and diode are correct and the transformers look good.  
With an RF probe I get zero volts on the xmit mixer output (U10 pin 4).
So I went back further and did some basic voltage checks and found some interesting results.  The key down voltage on the anode of D7 is
0 v when it should be 8 v.  The anode voltage on D6 is 0.645 v on key down instead of 0 v.  On receive it is 8v.

I'm having some trouble getting my head around how this relates to my lack of output power.  Another symptom I'm having is that the menu and display controls cease to function when I plug in a straight key.  But they work ok with a paddle attached.

I feel a headache starting.  Any suggestions on how to proceed?

Dazed and confused,
Bill, WV1N
     
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[Don Wilhelm-4]

Bill,

For the headache, take 2 aspirin and call me in the morning! :-)

Since you do not have 8 volts on the anode of D7 during transmit, that
says the 8T voltage rail is not producing voltage, and that 8T voltage
is needed to power the transmit mixer and a few other transmit stages -
so bottom line, it will not transmit without voltage on the 8T voltage rail.

The source of your problem is on the control board, and involves Q1 and
Q3 as well as the TX output from the MCU.  During Transmit (or better a
TUNE), the gate of Q3 should go to +5 volts, and its drain should go to
zero volts.  If the gate of Q3 is at 5 volts and the drain does not go
to zero volts, then Q3 is damaged.

The action of Q3 in turn should make Q1 conduct with the emitter at
about 8 volts and the base at a lower voltage (by more than 0.6 volts) -
in other words less than 7.4 volts on the base of Q1.  If those
conditions are true, then Q1 will conduct and 8 volts will appear at the
collector of Q1.

73,
Don W3FPR

On 3/2/2012 7:50 PM, William Schmidt wrote:

> I just finished up the RF board and am proceeding to the testing.  Much to my dismay, however, I got no power output when I tried to
> adjust the 40 m BPF.  I'm getting 13.5 v to all of the collectors and I pull 220 ma on receive and 420 ma on tune.
> The RF detector resistors and diode are correct and the transformers look good.
> With an RF probe I get zero volts on the xmit mixer output (U10 pin 4).
> So I went back further and did some basic voltage checks and found some interesting results.  The key down voltage on the anode of D7 is
> 0 v when it should be 8 v.  The anode voltage on D6 is 0.645 v on key down instead of 0 v.  On receive it is 8v.
>
> I'm having some trouble getting my head around how this relates to my lack of output power.  Another symptom I'm having is that the menu and display controls cease to function when I plug in a straight key.  But they work ok with a paddle attached.
>
> I feel a headache starting.  Any suggestions on how to proceed?
>
> Dazed and confused,
> Bill, WV1N
>    
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Alan Davenport]

Bill,
 
   I can answer your issue about the key. Make sure you use a STEREO plug. If you use a mono plug it will behave as you describe.
 
    Good luck with your no-power issue. I had the same thing which I eventually tracked down to a solder bridge on the control board. Hang in there.
 
    73 de Al, W2GZN
 

________________________________
 From: William Schmidt <[hidden email]>
To: [hidden email]
Sent: Friday, March 2, 2012 7:50 PM
Subject: [Elecraft] K2 alignment and test, part III problem
 

I just finished up the RF board and am proceeding to the testing.  Much to my dismay, however, I got no power output when I tried to
adjust the 40 m BPF.  I'm getting 13.5 v to all of the collectors and I pull 220 ma on receive and 420 ma on tune.
The RF detector resistors and diode are correct and the transformers look good. 
With an RF probe I get zero volts on the xmit mixer output (U10 pin 4).
So I went back further and did some basic voltage checks and found some interesting results.  The key down voltage on the anode of D7 is
0 v when it should be 8 v.  The anode voltage on D6 is 0.645 v on key down instead of 0 v.  On receive it is 8v.

I'm having some trouble getting my head around how this relates to my lack of output power.  Another symptom I'm having is that the menu and display controls cease to function when I plug in a straight key.  But they work ok with a paddle attached.

I feel a headache starting.  Any suggestions on how to proceed?

Dazed and confused,
Bill, WV1N
                         
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