[Elecraft] [K2] TX Issue in Part III checks

[Brian Handy]

I checked the resistors, and they all look right.

Seems like the plan of attack is to replace Q11 and Q13, and have a hard look at 
T4 ... I may rewind that just to take the moral high ground. Check the base 
voltage on the finals again and make sure it's below 0.64 before installing the 
high-ticket items.

Thanks a bunch!

Brian AE7JW



----- Original Message ----
From: Don Wilhelm <w3fpr at embarqmail.com>
To: Brian Handy <holy_tire_iron at yahoo.com>
Cc: elecraft at mailman.qth.net
Sent: Sun, January 9, 2011 11:38:28 PM
Subject: Re: [Elecraft] [K2] TX Issue in Part III checks

  Brian,

I did not respond to your original problem of high current.  A HiCur 
problem combined with low or zero output normally indicates a problem in 
the Low Pass filter and/or T4.

Your voltage on the base of the PA transistors is a bit high - I do not 
like to see anything higher than 0.64 volts, so check the resistor 
values connecting to Q11 and Q13.  When you receive the K2PAKIT from 
Elecraft, it will have replacement transistors for Q11 and Q13, and I 
would suggest using them.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:
> Hi All,
>
> I've been working on my K2 and I'm on the home stretch.  I had to dabble a bit
> to find a cold solder joint in the Part II checks, but eventually got a
> home-brewed test oscillator to reach through on 40m!  Quite happy with things 
>so
> far, and learning a lot.
>
> I still have a lot to learn about the transmitter side though, that doesn't
> work.  When I first hit 'tune' in the Part III checks, I noticed high current 
>on
> the power supply, high current on the front panel, and changing the power 
level
> didn't help, it was always high draw.
>
> It didn't take much of this to zorch the PA finals and short things straight 
to
> ground.  Nothing worked until I pulled T3, and while I had the soldering out I
> took out the PAs and started looking around and reading the mail archives.
>
> I noted one suggestion from Don to someone else and checked the voltages on 
>base
> on the finals - both are around 0.65V, which I think is OK.
>
> I realize things won't be quite the same without the PAs there and proper
> feedback happening, but ... I then started going through all the voltages on 
>the
> RF board with TUNE on.  Everything looked pretty much fine except for Q24 ~
>
> Leg - Expected - Measured:
> G    - 0V - 5.6V
> S - 1.2 - 2.5V
> D - 13V - 0V
>
> That doesn't look right at all to me.  Exploring further, I started chasing 
>VALC
> down the rabbit hole.
>
> Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in
> TUNE.  I decided that was OK.
>
> Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V.  Finally
> the emitter of Q8 (V ALC) seems stuck at 7.4V.
>
> I was firmly confused at this point, so went back and started checking Control
> Board voltages per the page of expected readings in the back of the manual 
with
> CAL FCTR turned on.  Everything seems turned off when I do that and I'm seeing
> pretty much 0V everywhere.
>
> I'm a bit saturated at the moment, but thought I would ask if this sounds like
> I'm on the right track, or if I have to get to poking elsewhere ...
>
>
>
> Cheers and thanks in advance,
>
> Brian Handy
> AE7JW
> Tokyo, Japan
>
>
>
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