[Elecraft] Re: K2: Frequency Counter Problem Solved
Jon Perelstein
jperelst at yahoo.com
Mon Oct 6 23:38:16 EDT 2008
It was the frequency probe.
I had already ordered another from Elecraft a while back. I put it together tonight and then ran the frequency counter test with the new probe and it read correctly. I then did the various alignment steps around pg. 67/68 and they all worked without problem.
I can't see anything wrong with the old one, but if everything is working right with the new one, I'll take it.
As always, thanks for your help.
Jon
KB1QBZ
--- On Sun, 10/5/08, Don Wilhelm <don at w3fpr.com> wrote:
From: Don Wilhelm <don at w3fpr.com>
Subject: Re: K2: Frequency Counter Problem (Was PLL Ref Oscillator Problem)
To: jperelst at yahoo.com
Cc: "elecraft reflector" <elecraft at mailman.qth.net>
Date: Sunday, October 5, 2008, 9:56 PM
Jon,
It is too early to tell if the RP5 pins 7 and 8 - 9 and 10 are any
problem. Those resistors are in the sidetone AF path, so put that
information away in a notebook and review it if you should encounter any
sidetone problems.
FB on finding good resistance readings on the rest of RP4.
As a wild guess, check the internal counter probe. The shield of the
coax should be closest to the left side panel if the internal counter
probe is expected to indicate properly.
Bottom line is that you have some problem with either the internal
probe, or that Control Board Q5 and Q5 circuits have a fault condition.
One possible guess is that you have some 2N5179s with marginal gain
characteristics. I would suggest replacing Q9 and Q10 with 2N2222
transistors as a trial. The frequency response of the counter may be
reduced a bit from the spec'ed 40 MHz, but it will still be greater
than what is required for internal testing of the K2. If you do not
have a stock of 2N2222 transistors, you will find 2 of them in the RF
Board bags. Use those to replace Control Board Q9 and Q10 and send a
request to parts at elecraft.com for replacement 2N2222 transistors.
Jon Perelstein wrote:
> I had the subject wrong when I wrote my first post on this. It is the
> Frequency Counter that's a problem and not the PLL Ref Oscillator.
>
> I've checked my soldering and all is okay. Where possible, I've
also
> run continuity tests, and all is okay. In addition, I've checked to
> make sure that I've used the correct components for the Frequency
> Counter.
>
> We had this discussion about soldering when I was building my K1, and
> the problem turned out to not be my soldering.
>
> I have tested the 4MHz crystal with an HT by holding the HT's antenna
> right near the 4MHz crystal. The HT was picking up a signal at 4MHz
> when near the 4MHz crystal (a trick you taught me).
>
> I'm in the processing of borrowing a signal generator and a frequency
> counter from another ham, and possibly an oscilloscope. Can I use
> them for the testing and aligning in place of the internal frequency
> counter, or is the frequency counter being used in other ways?
>
> The manual says that there may be a frequency counter probe problem.
> I've cut the shrink wrap off the probe to check it, but don't see
> anything wrong. Any suggestions as to what I should look for or test
> in the construction of the probe?
>
> Assuming that I've soldered everything correctly, what other
> possibilities are there that might be causing the frequency counter
> problem? What else can I test?
>
> I did notice one strange thing -- when I tested RP5, I tested all the
> pairs, even though some are not used for the frequency counter. Pairs
> 7&8 and 9&10 each tested out at 248 ohms and not 470 ohms. Pairs
1&2,
> 3&4, and 5&6 did test out at 470 ohms. I have to admit to being
rusty
> at reading complex schematics like the K2, but I don't see anything
> that would cause pairs 7&8 and 9&10 to test out at 248 ohms when
> mounted on the Control Board (especially because the Control Board was
> NOT plugged into the RF board when I tested the resistance in RP5).
> Is this a problem?
>
> Jon
> KB1QBZ
>
>
> --- On *Sat, 10/4/08, Don Wilhelm /<w3fpr at embarqmail.com>/* wrote:
>
> From: Don Wilhelm <w3fpr at embarqmail.com>
> Subject: Re: [Elecraft] K2: PLL Reference Oscillator Problem
> To: jperelst at yahoo.com
> Cc: "elecraft reflector" <elecraft at mailman.qth.net>
> Date: Saturday, October 4, 2008, 12:03 AM
>
> Jon,
>
> That check of the 4 MHz reference is there to help you determine the
> correct functioning of the internal counter probe - it has nothing to
do
> with the frequency, but the reading should be steady at 4000.00 MHz
> (plus or minus 1 count in the last digit).
>
> Since your results were variable (it should show a rock solid 4 MHz),
> something is wrong with your probe or with Control Panel Q9 or Q10 and
> their associated components. Check your soldering carefully. If you
do
> not know what a good solder connection looks like, I refer you to the
> soldering article on the Elecraft website. A good solder connection
> looks like a 'mountain' with a concave slope to it. If your
solder
> connections are convex (look more like 'balls of solder', then
the
> solder pads did not receive enough heat and you have applied excess
> solder. Wick away the excess and be sure the solder tapers off to an
> almost invisible edge on both the solder pad and the component lead.
I
> mention this repeatedly because the most common cause of builder
failure
> is excessive solder and inadequate heating of both the solder pad and
> the component leads.
>
> You must get a good reading at the 4 MHz reference oscillator test
> before proceeding to anything else.
>
> Yes, you could have a bad component, but that is way down on the list
of
> failures. Check the values of RP4 and RP5 on the Control Board, and
Q9
> and Q10.
>
> 73,
> Don W3FPR
>
>
> Jon Perelstein wrote:
> > On page 47 of the manual, I was testing the frequency counter. I
put
> > the counter probe tip to the left side of C22 (actually, it
wasn't
> > clear which left side, but I put it to the left facing the panel
as it
> > is mounted in the radio). The LCD was jumping all over the
place,
> > from about 00200 to about 04200. As I held it there, it tended
to
> > move toward the area of 04000, but it never stabilized in any
way.
> >
> > I went ahead and built more of the radio to get to page 63. When
I
> > attempted the 4MHz Oscillator Calibration on pg 63, I got
0000.00.
> >
> > I'm not sure where to proceed from here. Help!!
> >
> > Jon
> > KB1QBZ
> >
> >
> >
> >
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