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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
