Don and the group, I have not yet solved this problem, but upon further troubleshooting a recurrent theme seems to be that the clock signal (SCK), which appears at pin 18 of MCU U6, pin 6 of EEPROM U7 and pin 10 of U8 on the control board, as well as pin 1 of DAC U5 on the RF board is constantly 5 volts when, according to the voltage charts, it should be 0 volts.
Further, the /DAC2CS value at pin 19 of the MCU U6 (control board), which is also at pin 3 of U5 (RF board) is 0 volts when it should be 5 volts. The only other anomalous voltage values on MCU U6 are 0.1 volt on SRDIN pin 33 instead of the listed 5 volts, and 0.2 volt on /SR RD pin 38 instead of the listed 1.2 volts in the chart. So my question is, what controls the SCK value on pin 18 of the MCU U6? In other words, I assume that there is another pin on U6 that controls whether pin 18 is high or low. If not, should I assume that the MCU is bad because it always reads high? Many thanks to anyone willing to wade through all this! -- Dave WB4JTT --- On Wed, 12/31/08, Don Wilhelm <w3...@embarqmail.com> wrote: > From: Don Wilhelm <w3...@embarqmail.com> > Subject: Re: [Elecraft] K2 PLL reference oscillator range is zero > To: wb4...@yahoo.com > Date: Wednesday, December 31, 2008, 1:53 PM > Dave, > > Yes, you should suspect U5 (or one of the digital signals > going into it). No need to look at pin 7 with a scope - the > output at pin 7 is analog and should remain a steady > voltage. > > Check the soldering of U5 and the /DAC2CS signal path back > to Control Board U6 pin 19 (there are connectors in the path > that could also be suspect. The inputs on pin1 and pin 2 > are shared with other digital devices on the Control Board, > and if you have checked for things like the presence of > sidetone, those signals (SCK and SDO) are working at their > source so should be OK although there are also the RF Board > to Control Board connections to consider as possible faults. > > 73, > Don W3FPR > > David Johnson wrote: > > Don, > > > > Thanks for the quick response! > > I do have the 5 volts on pin 8 of U5, but a constant > 0 volts on pin 7 even when tapping the Band + and Band - > switches. But I'm just looking at it with a Digital > Voltmeter, not a scope so maybe I'm missing it. > > > > Pin 5 of U6 is 4 volts, so at least that data point > is OK. > > > > Should I suspect U5 at this point? What can I do to > verify that U5 is being properly triggered at its input when > I tap the Band + and Band - switches? > > > > Thanks again. > > > > -- Dave WB4JTT > > > > > > --- On Wed, 12/31/08, Don Wilhelm > <w3...@embarqmail.com> wrote: > > > > > >> From: Don Wilhelm <w3...@embarqmail.com> > >> Subject: Re: [Elecraft] K2 PLL reference > oscillator range is zero > >> To: wb4...@yahoo.com > >> Cc: elecraft@mailman.qth.net > >> Date: Wednesday, December 31, 2008, 2:56 AM > >> Dave, > >> > >> Yes, do check U5, but ignore the voltages on pins > 1, 2 and > >> 3 because they are digital and the active state > may not > >> correspond with the voltage measured with a DMM. > >> U5 pin 8 must have 5 volts DC for the chip to work > - if > >> that is not true, stop (all other tests are > futile). > >> > >> Next monitor the voltage at U5 pin 7 while tapping > BAND+ > >> and BAND-. the voltage should go to 4 volts or > more when > >> BAND+ is tapped and to nearly zero volts when > BAND- is > >> tapped. If that is true, then U5 and its driving > digital > >> signals are OK. > >> > >> Next thing to check is U6 - check at pin 1. The > voltage > >> when BAND+ is tapped should be near 8 volts and > when BAND- > >> is tapped should be near zero volts. If U5 pin 7 > was OK, > >> but this test fails, the fault is likely with U6 > or the > >> thermistor board. > >> > >> To give a quick check on the thermistor board, > measure the > >> voltage at U6 pin 5 - it should be 4 volts (or > more > >> precisely, 1/2 of the 8 volt regulator voltage. > >> > >> If the U6 pin 1 output is correct, there is not > much more > >> to check. R19 should have a similar voltage swing > (between > >> BAND+ and BAND-), and the voltage on varactors D16 > and D17 > >> cathodes should be similar. > >> > >> If all checks out so far, blame X1 or L31. > >> > >> Remember that since this K2 worked properly > before, there > >> should be only a single failure. Your challenge > is to find > >> the source. > >> > >> 73, > >> Don W3FPR > >> > >> > >> David Johnson wrote: > >> > >>> Hello and Happy New Year to everyone. > >>> > >>> I have owned K2 serial no. 3980 for about > five years > >>> > >> and it has worked flawlessly. A couple of days > ago it > >> stopped tuning properly. Instead of tuning across > a signal, > >> it now acts like a crystal controlled radio that > tunes in > >> discrete steps of approximately 10 khz as the knob > is > >> rotated. > >>> This same problem was described on this list > just > >>> > >> last month by Jon, KB1QBZ, and he said that he > solved it by > >> redoing the alignment and test steps, part II. So > I began > >> by redoing the 4 MHz Oscillator Calibration, which > gave me a > >> frequency of 12.086 Mhz. > >> > >>> The next step is the PLL Reference Oscillator > Range > >>> > >> test, but I got no change in the 12.086 Mhz > indication by > >> tapping either the Band + or Band - switch. > >> > >>> So I measured the voltages on U6, and got 0 > volts on > >>> > >> pins 2, 3 and 4 at all times, with no change as I > tapped the > >> Band + and Band - switches. I also got a steady > 2.0 volts > >> on pin 7. I know these voltages are supposed to > change as > >> you tap the Band + and Band - switches, but is > this > >> something that you can see on a digital voltmeter, > or is it > >> something instantaneous that you need to view with > an > >> oscilloscope? > >> > >>> I backed up and measured voltages on U5. I > got 5V > >>> > >> on pin 1, and 0 volts on pins 3 and 4, all > opposite of what > >> the voltage table lists. I also got 0 volts on > pin 7 > >> continuously even when I tapped the Band + and > Band - > >> switches. > >> > >>> Finally I looked at the thermistor board, > but I > >>> > >> wasn't sure quite how to investigate it. I > have 1.2 > >> volts at the junction of RA/Rt/RB and 0 volts at > the > >> junction of RB and RC. > >>> Are my symptoms consistent with a bad > thermistor, or > >>> > >> is this more likely to be a failure within U5 or > U6? > >> > >>> Sorry for taking up all this bandwidth but I > am not > >>> > >> sure what my next step should be. > >> > >>> Thank you for any and all suggestions on how > to > >>> > >> proceed. > >> > >>> -- Dave WB4JTT > >>> > >>> > > _______________________________________________ > > Elecraft mailing list > > Post to: Elecraft@mailman.qth.net > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > ------------------------------------------------------------------------ > > > > > > No virus found in this incoming message. > > Checked by AVG - http://www.avg.com Version: 8.0.176 / > Virus Database: 270.10.1/1869 - Release Date: 12/30/2008 > 12:06 PM > > > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
