[Elecraft] [K2] KSB2 Module Question

[Brian Handy]

Don,

Thanks for the note.  TUNE seems to work fine now, and I have no explanation for you why fiddling with T1 would have any effect on this.  But the levels you suggest  below to check are all in line, and when I plug in the dummy load I see power there.  It appears, at first blush, to be working.

What isn't cooperating is ALC THR.  I see 6V on U2-5 and U4-3 when I should be seeing 0.6V.  Could you give me a little insight into how this part of the circuit works?  

Kind regards


Brian AE7JW


________________________________
 From: Don Wilhelm <w3fpr at embarqmail.com>
To: Brian Handy <holy_tire_iron at yahoo.com> 
Cc: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net> 
Sent: Sunday, March 17, 2013 12:52 AM
Subject: Re: [Elecraft] [K2] KSB2 Module Question
 
Brian,

You may have had a problem with T1, but that is not in the transmit path 
for a TUNE operation, so you have another problem to find if I 
understood your post correctly - no power output during a TUNE operation.

TUNE uses the same path as CW, and the path for CW through the KSB2 is 
short.
The BFO signal enters at P1 pin 12, goes through C42 then through diode 
D3 and on to the base of Q3.
In order for that to happen, D3 must be conducting - the TXC signal 
applies voltage to the cathode to forward bias D3, so be certain there 
is at least 2.5 volts on the cathode.
Q3 must also conduct - again the TXC signal biases the Q3 base in 
addition to D3.  The 8T signal voltage flows through D5 (you should have 
7+ volts on the cathode of D5 and the collector of Q3.
With those conditions present, the BFO signal should go through C39 and 
exit at P1 pin 7.

The voltages I mentioned are only valid for CW transmit or a TUNE.

73,
Don W3FPR
On 3/16/2013 8:27 AM, Brian Handy wrote:
> Dear Readers,
>
> I am right now working on the KSB2 module.  It's built, been installed into my K2, and I was able to hear a few stations with it.  This gave me a false sense it was working, which is not actually true.
>
> I now find that when I put the K2 into TUNE with this gizmo installed, I don't make power:  set 5W on the dial, and get 0.1 indicated when I hit the TUNE button.  I started going back through the DC measurements in RX mode and have turned up the following:
>
> U2-5:  6V (should be 0.6)
> U4-3:  6V (should be 0.6)
>
> These are the ALC THR voltage, seemingly coming out of U2.  I looked up the specs for U2 and I'm not quite sure what to do with this information.
>
> What does this potentially mean?
>
>
> Cheers
>
> Brian Handy AE7JW
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