Posted by
Don Schroder on
Sep 27, 2018; 5:43pm
URL: http://elecraft.85.s1.nabble.com/K2-Alignment-and-Test-Part-II-issues-tp7645364p7645372.html
Don,
Board U6 pin 5
Thank you for the suggestions! The DC voltage at RF Board U6 pin 5 is 0 volts. In fact, all pins of U6, except pin 6, are 0 volts. Pin 6 is less than 1 volt.
I saw a bridge between C96 and RFC10, the schematic shows these two components connecting together, so that should be ok. I’m still looking for bridges.
Could you elaborate a little on the ^voltage rail*? How do I identify the rail on a schematic, or can I? Which component is the 8 volt regulator? I feel I should know the answers to these questions, I must be having a senior moment. Your help and advice is much appreciarted!
Thanks!
Don, KE0PVQ
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Sent: Thursday, September 27, 2018 11:01 AM
To: Don Schroder<mailto:
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Subject: Re: [Elecraft] K2 Alignment and Test, Part II issues
Don,
First check the DC voltage at RF Board U6 pin 5 - it should be 4 volts
(or 1/2 the 8 volt regulator output voltage). If it is not correct, you
have a problem with the thermistor board - most likely a solder bridge.
You should have 8 volts at the thermistor board pin 8. If that is not
correct, look carefully for solder bridges. That 8 volts comes directly
from the 8 volt regulator voltage rail.
It does sound like you have a problem with the PLL Reference Oscillator,
but your voltage measurements on the thermistor board pins should be
investigated first before drawing any other conclusions.
Make sure you have good results with the PLL range tests just after that.
The exact frequency of the 4 MHz Oscillator is not critical at this
point - for now it only substantiates that the oscillator is working. If
you put a probe on C22, it will pull the frequency. If your frequency
counter is sufficiently accurate, wait until you have a good frequency
at TP1, and then measure the frequency with both the counter and the
internal counter probe using CAL FCTR. Adjust C22 so CAL FCTR frequency
is the same as your external counter.
I do not know the accuracy of your counter, but mine is accurate to 10
exp-9 and I can set C22 with it for good K2 Dial Calibration. There are
other methods for setting C22 that do not depend on the accuracy of your
frequency counter. When you can receive WWV at 10 or better 15 MHz,
look at my website www.w3fpr.com article on K2 Dial Calibration to
accurately set C22 and achieve good K2 dial calibration.
73,
Don W3FPR
On 9/26/2018 8:14 PM, Don Schroder wrote:
> Hi folks,
>
> Got to the subject location on my K2 kit #7818, and am having some difficulties with the tests. My frequency counter, when touched to the left side of trimmer capacitor C22, reads 3999.98 on the LCD. This makes me believe there is no problem with the frequency counter probe that I assembled.
>
> On page 63, under *4 MHz Oscillator Calibration, I selected CAL FCTR, and the LCD displays a rapidly changing frequency between 185.~ to 188.~. It does not show a frequency of 12090 kHz suggested by the manual. This tells me I have a problem with the PLL Reference Oscillator (since the frequency counter probe appeared to be ok). I then decided to check voltages, and discovered that I am missing some +5v signals from U4 and U5.
>
> Any suggestions on where to look next? I’d like to trace the 5v signals, but I don’t see how to do that using the schematics. I did measure voltages on the 8 pins of the Thermistor Board, they were all 0 volts! That didn’t seem right, either.
>
> Appreciate any suggestions! Thanks!
> Don, KE0PVQ
>
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