[Elecraft] Possible solution: K1 with a strange XFIL problem...

Tue Sep 23 02:59:23 EDT 2014

Closing this topic - 

Bruce's suggestion to check that the RIT/XIT switch legs nearest the
outside edge of the PCB, were not touching the adjacent solder joints on
the back side of the adjacent single row header was exactly right.  My
radio was making contact between the switch leg and pin 5 of the header.
The clearances there are very small to the point where I'm not sure that
a visual inspection would have pointed this out to me if I had not
specifically been looking at that pin. 

I fixed this and the problem is fully resolved. 

Thanks Bruce!

Dave

On Mon, Sep 22, 2014, at 09:38 AM, David Beal wrote:
> Thank you Bruce! 
> 
> Your description below aligns closely with what I had found previously
> where I learned that when changing the bandwidth of FL2 to approach that
> of FL3, the problem followed the filter bandwidth and not the switch
> position itself. I knew it was a voltage problem but hadn't had success
> to track it further. I'll take a look at the switch this week. 
> 
> 72
> Dave
> AE6RQ
> 
> 
> 
> 
> On Mon, Sep 22, 2014, at 04:36 AM, Bruce Beford wrote:
> > Yes I had this exact problem on one I repaired in July of 2012. It was
> > traced to a short between the RIT/XIT switche to a trace on the board,
> > where
> > the switch lead had been bent over by the original builder before
> > soldering.
> > 
> > I corresponded with Don Wilhelm about this. Though he didn't provide the
> > solution, our conversation led me to the tests that found it. Copied
> > below
> > is  a repost of my last message to Don, after I resolved it. I don't
> > recall
> > if I posted this to the reflector or not. In any event, It may help
> > someone
> > in the future. I have a photo of the offending switch pin connection, if
> > anyone wants it.
> > Bruce Beford, N1RX
> > 
> > Hi, Don.
> > You may recall that I posted recently to the list about a strange problem
> > with a K1.  I resolved it today, and wanted to share the results with
> > you.
> > Here's a copy of my original post:
> > 
> > OK, folks.
> > Time to put on your thinking caps...
> > I just purchased a used K1. Has NB, ATU and 4 band board, set for
> > 7/10.1/14/21 MHz. All appears to be operating normally, except...
> > When cycling through the crystal filter bandwidths from FL1-FL3, once FL3
> > is
> > reached, all buttons become unresponsive. The VFO readout still works,
> > but
> > the MCU will not respond to any key presses. The filter does actually
> > switch
> > to the narrowest setting, based on the audio response. Cycling the power
> > returns the rig to normal operation (on FL1), and all works fine again
> > until
> > trying to use FL3.
> > 
> > About the only other anomaly I notice is what seems to be a louder pop in
> > the speaker when switching in RIT or XIT than I remember from my last K1.
> > I
> > have not yet begun any troubleshooting (except for a full reset). Just
> > thought I would poll the collective wisdom here before digging in.
> > Actually,
> > I'll be getting ready for Lobstercon over the next couple of days, so I
> > don't know how much time I'll be able to commit until after the weekend.
> > 
> > ----------------------------------------------------------------------------
> > 
> > You and I both suspected a problem with the MCU, as there should no other
> > circuitry involved, except the DAC and EEPROM. You also suggested perhaps
> > replacing those ICs while in there.
> > 
> > Fortunately, I have a friend who allowed me to borrow his working K1.
> > Swapped the entire Front Panel board, mine works fine with his board. I
> > then
> > took his MCU chip and put it in my board, still have the problem. So, the
> > problem was on my FP board, but not the MCU. 
> > 
> > One thing I did notice was a ticking noise in the audio with no antenna
> > connected, almost like ignition noise in a vehicle, when using my board
> > FP
> > board but not when using my friend's. The ticking would disappear when I
> > went to FL2. Ahh, another clue...
> > 
> > I then decided to remove the DAC from my board and see what happens. Lo,
> > The
> > unit would now switch properly, FL3,FL2,FL1 and back to FL3 OK. Of
> > course,
> > it was not actually switching the filter bandwidth with the DAC out. I
> > now
> > had a pretty load, almost moterboating noise in the audio. 
> > 
> > I decided to ground what was the XFIL/TONE output pin of the DAC (pin 1)
> > to
> > see if it would quiet the audio. It did, BUT- it activated the RIT! Wait
> > a
> > minute- there should be no connection between the two.... but, there was.
> > Upon extra careful inspection, I found that one lead on the RIT/XIT
> > switch
> > was not inserted through the board by the original builder. It was bent
> > over, and was contacting pin 5 on J1 (the XFIL/TONE signal). The
> > "moaterboating" I heard was actually the MCU driving the LCD pin and
> > polling
> > the input for the switch. This was not noticeable when the DAC was
> > holding
> > this line at a steady DC voltage.
> > 
> > So, what was happening was when the DAC output it's lowest voltage for
> > FL1
> > (about 1.6 volts), it would tickle the input pin on the MCU for the
> > WPM+/FILTER switch. I believe the MCU would think the switch was being
> > held
> > in, therefore no other switches would work, until the unit was powered
> > off.
> > An original symptom (which I didn't recognize at the time) was when I
> > noted
> > that the RIT/XIT button seemed to generate an audio pop when used. That's
> > because it was grounding the XFIL/TONE signal line.
> > 
> > I reworked the switch connection, and all is fine now. I have attached a
> > photo of the offending pin (not  a good shot, but shows the connection in
> > question). I thought you might like to hear about this one.
> > 
> > Thanks for being a "sounding board", Don. I appreciate it.
> > 73,
> > Bruce, N1RX
> > 
> > 
> > 
> > 
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Elecraft at mailman.qth.net
> > 
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to aardvarq at operamail.com
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to aardvarq at operamail.com