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

Mon Sep 22 12:38:32 EDT 2014

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
> 
> 
> 
> 
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