[Elecraft] K2 PLL Reference Osc Range Low

[Jim KO5V]

Hi Don,

Thanks for the reply. I did the voltage checks that you suggested, and all look good. For U6 pin 1, "near 8V" is 7.6V. I hope that's close enough.

Ray, SM5LXP, emailed that he had seen the same problem, and it was found to be a faulty L31. So today, I got another one and replaced it. Sure enough, the range went to 13.5kHz. 

Unfortunately, there are still a couple of glitches:

1. For the VCO voltage range readings, all were well within spec with L30 adjusted to 6.0V @ 4000KHz, except the voltage at 7000kHz. It was 1.26V. I had to adjust L30 to 6.67V (@4000kHz) to get a reading of >1.50V @ 7000kHz. All others are still well within range. Is this OK, or should I be looking for a problem?

2. I get a 0000.00 reading for the BFO test. I checked the continuity of L33 via the leads of R116 on the top of the board. That looks good (1.3ohms). I replaced the 2 XTALS, with no change, and have checked that diodes, and capacitors are all the correct parts. The soldering looks good.

Now, what's probably a dumb question: I have an XG-2 signal generator. To perform the tests in the troubleshooting section of the manual (pages10&11), Does the output level of the XG2 matter (50uV, vs 1uV)?
I'm not sure I did this correctly before (I used the 40M band).

Thanks again, & 73, Jim KO5V


-----Original Message-----
>From: Don Wilhelm <w3fpr at embarqmail.com>
>Sent: Jun 1, 2012 2:58 PM
>To: Jim KO5V <ko5v at earthlink.net>
>Cc: elecraft at mailman.qth.net
>Subject: Re: [Elecraft] K2 PLL Reference Osc Range Low
>
>Jim,
>
>You are correct, the problem likely will be found in the soldering of 
>the Thermistor board.  Do these tests to see if it indicates the problem 
>source.
>
>Check the voltage at U6 pin 5.  It should be 4 volts - if not, you have 
>a thermistor board problem
>Enter the menu for CAL FCTR - then tap BAND+ and measure the voltage at 
>U5 pin 7 (should be near 4 volts) and the voltage at U6 pin 1 (should be 
>near 8 volts).  If those are not correct, you have a problem with the 
>thermistor board.
>If you got close to 8 volts at U6 pin 1 in the last step, check the 
>voltage at the cathodes of D16 and D17.  If the voltage is not close to 
>the same thing you read at U6 pin 1, you have a soldering problem at R19 
>or RP2 or D16 or D17.
>
>If all checked out this far, tap BAND- and read the voltage at U5 pin 7 
>and U6 pin 1 - this time both should be near zero.
>
>Let me know what you find.
>
>73,
>Don W3FPR