BFO Test fails

[kruegerbenny]

Hello,

my BFO test failed (it shows 0.0000 Hz). After checking the right values of the parts, I made some measurements with an oscilloscope. Here the results:
Between C174 and C173 : signal with a frequency of 8,06MHz (720mV peak).
Results @ RP6:
Pin2/Pin8 : no Signal
Pin4: 8,37MHz (116mV peak)
Pin5: 8,43MHz (42mV peak)

L33 seems to be ok(I made an resistor check of R16 : 1.5 Ohm)

Anybody an idea?

Thanks

[Don Wilhelm-4]

  Name and call please - now required by reflector guidelines.

I assume this is a K2 - although you did not state it, it only makes
some sense with the K2.

Is the internal counter probe working?  What do you get when in CAL FCTR
if you plug the probe into TP3 or TP1?

The BFO frequency of the K2 should be near 4915 kHz.  At U11 pin 6, the
BFO signal should be at least 200 mV peak to peak (70 mV RMS).

73,
Don W3FPR

On 12/3/2010 9:29 AM, kruegerbenny wrote:

> Hello,
>
> my BFO test failed (it shows 0.0000 Hz). After checking the right values of
> the parts, I made some measurements with an oscilloscope. Here the results:
> Between C174 and C173 : signal with a frequency of 8,06MHz (720mV peak).
> Results @ RP6:
> Pin2/Pin8 : no Signal
> Pin4: 8,37MHz (116mV peak)
> Pin5: 8,43MHz (42mV peak)
>
> L33 seems to be ok(I made an resistor check of R16 : 1.5 Ohm)
>
> Anybody an idea?
>
> Thanks

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[kruegerbenny]

Yes, its a K2 (sorry)
The internal counter probe works, already tested in the earlier tests
At U11 pin 6, I got a signal with 4.930kHz (2,4V peak to peak)

Any idea?

[Don Wilhelm-4]

  Do you have voltage at the drain of Q24 when in CAL FCTR?  You must
have voltage in order for the signal to pass through Q24.
If so, then trace the BFO signal with your 'scope.
Both ends of L33
Then through D37
Then to the gate of Q24.
Then the source of Q24.

Let us know where the signal is lost.

I will provide additional help when you sign your posts with your name
and callsign.  This is a reflector of other users, not a support
organization, even though some of us do offer support here - anonymity
is not really welcomed.

73,
Don W3FPR

On 12/3/2010 4:02 PM, kruegerbenny wrote:
> Yes, its a K2 (sorry)
> The internal counter probe works, already tested in the earlier tests
> At U11 pin 6, I got a signal with 4.930kHz (2,4V peak to peak)
>
> Any idea?
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[kruegerbenny]

oh, i think i measured @ U11-P7 instead of P6. But when I measured again, there was a signal with ~8.1MHz and 1.5V peak-to-peak.....
U11-P7: no signal

Benny

[kruegerbenny]

Q24: 5,76V

L33(left): 8,33MHz(240mV peak-to-peak)
L33(right): no signal (i think here is the lost)


I have to admit that I don't have a call sign yet, but I'm already learning for the "exam" (I'm a student a had a lot to do the the last months..)

Thanks for your help

Benny

[Don Wilhelm-4]

  Benny,

Thanks for providing your name, and very good luck on acquiring your
amateur license.
I am also adding K2 to the subject - some here like to filter by rig type.

OK, first the frequency is wrong, are you certain you have the time
scale on your 'scope calibrated?  The K2 BFO crystals should be marked
for 4915 kHz (or something near that) - check those markings first.

Then check continuity through L33 with your ohmmeter - it is best
checked from the top of the board which will check for improperly
soldered connections too.  If the resistance is quite high, you may have
an open L33 or an improper solder connection.

Also check D37 to be certain it is not installed backwards - that could
kill the BFO signal.

Check for a solder bridge at pins 3, 4, 5 and 6 of RP6 - that also will
kill the signal.

73,
Don W3FPR


On 12/3/2010 4:50 PM, kruegerbenny wrote:

> Q24: 5,76V
>
> L33(left): 8,33MHz(240mV peak-to-peak)
> L33(right): no signal (i think here is the lost)
>
>
> I have to admit that I don't have a call sign yet, but I'm already learning
> for the "exam" (I'm a student a had a lot to do the the last months..)
>
> Thanks for your help
>
> Benny

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[kruegerbenny]

crystal values checked -> ok
continuity of L33 checked -> ok
D37 is correctly installed
and I resoldered all pins of RP6

any other ideas?

(how can I check if the crystals are ok?)

Benny

[Don Wilhelm-4]

  Benny,

Well, if all that is OK, then it should work unless there is a problem
with Q24.  Check the value of C169 as well as C173 and C174.

It is particularly worrysome that you are seeing something around 8 MHz
at pin 6 of U11.  Please tell us how you are measuring that frequency
('scope or frequency counter).

If indeed you are getting an 8 MHz signal, you may have bad crystals at
X3 and X4, but that would be quite unusual.
There is not an easy method of checking the crystals.

You may want to beg parts(at) elecraft(dot)com for replacement BFO
crystals and a replacement L33.

Please include your name on all posts to this reflector.

73,
Don W3FPR

On 12/3/2010 7:03 PM, kruegerbenny wrote:
> crystal values checked ->  ok
> continuity of L33 checked ->  ok
> D37 is correctly installed
> and I resoldered all pins of RP6
>
> any other ideas?
>
> (how can I check if the crystals are ok?)
>
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[Don Wilhelm-4]

  Benny,

Additional thoughts - check D38 for correct orientation.
Try putting a jumper from the junction on L33, X3 and X4 to see if you
get oscillation at 4915 kHz or something close to that frequency - if
you do, the crystals are OK and your problem is with L33, D37, C169 or Q24.

73,
Don W3FPR


On 12/3/2010 7:03 PM, kruegerbenny wrote:
> crystal values checked ->  ok
> continuity of L33 checked ->  ok
> D37 is correctly installed
> and I resoldered all pins of RP6
>
> any other ideas?
>
> (how can I check if the crystals are ok?)
>
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[kruegerbenny]

I will do the tests tomorrow, but one question:
A jumper from junction of l33,x3 and x4 to where?

Benny

[Don Wilhelm-4]

  Benny,

To ground.

73,
Don W3FPR

On 12/3/2010 8:15 PM, kruegerbenny wrote:
> I will do the tests tomorrow, but one question:
> A jumper from junction of l33,x3 and x4 to where?
>
> Benny
>
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[kruegerbenny]

So, hello again.

First of all i want to excuse but I give you some false informations. The 8.x MHz signal I measured was/is at Pin 7, not Pin 6 of U11. I did the test with grounding L33/X3/X4 and there's some interesting behaviour (at Pin 7):
When I ground L33/X3/X4 and then measure the signal, it is about 7.7MHz. By removing the jumper(to ground), the frequency changes to 4.9MHz(by removing the probe and connect it again, the 8.02MHz signal appears again).

After that, I changed the order of instructions:
Now I connect the probe at P7(U11) and then ground L33/X3/X4. The result: Before grounding 8.02MHz, after grounding 4.9MHz (also when I remove the jumper)

At Pin6 of U11, there wasn't any signal all the time.

Benny

[Don Wilhelm-4]

  Benny,

Actually you should have a better signal at U11 pin 6 than you do at pin
7, but let that go for right now (we may get back to it if necessary).

So you do get the proper BFO frequency when grounding the crystals, and
as I recall you measured a low resistance across L33, so it should have
continuity - all that should be good.

Now, monitor the oscillation at U11 pin 6 (or pin 7) while you ground
the side of L33 that is NOT connected to X4 and X5.
Ignore any oscillation other than the 4.9 kHz because that is what you
are looking for.

If you get a 4.9 kHz oscillation with the low end of L33 connected to
ground, then check the value of C172 - it should be 0.01 uF (marked
103).  Also verify again that D37 is mounted the "right way 'round".

If you cannot get a 4.9 kHz oscillation with the lower end of L33
grounded, inspect the soldering of those fine wires to the leads of the
1/8 watt resistor very carefully - and make sure what you used for that
high value 1/8 watt resistor was the correct item.  It is a very high
value resistor, and is actually used as an effective insulator across
L33 to both solder the fine wire leads and secure L33.  If you used
anything else, that could cause your problems.

73,
Don W3FPR

On 12/4/2010 1:47 PM, kruegerbenny wrote:

> So, hello again.
>
> First of all i want to excuse but I give you some false informations. The
> 8.x MHz signal I measured was/is at Pin 7, not Pin 6 of U11. I did the test
> with grounding L33/X3/X4 and there's some interesting behaviour (at Pin 7):
> When I ground L33/X3/X4, the measured signal is about 7.7MHz. By removing
> the jumper(to ground), the frequency changes to 4.9MHz.
>
> After that, I changed the order of instructions:
> Now I connect the probe at P7(U11) and then ground L33/X3/X4. The result:
> Before grounding 8.02MHz, after grounding 4.9MHz (also when I remove the
> jumper)
>
> Benny
>
>

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[kruegerbenny]

Hi,

grounding of L33 doesn't bring the expected signal (7.xMHz). D37 seems to be mounted the right way (round caps in direction to front panel).
If I put a resistor parallel to R116(it should be the right one: grn-brw-grn-(gold)), i get the 4.9MHz oscillation, but still no signal at TP2 (in this case, i get the following frequencies by contacting the int. probe to U11-P7: 4918.75 and 4916.12).

Benny

[Don Wilhelm-4]

  Benny,

R116 is supposed to be a very high value resistor - in fact, it would be
best if it were actually an insulator, but 5.1 megohms is sufficiently
high to serve that purpose.  The only reason the resistor is provided is
that it produces both a mounting anchor for L33 and its leads provide a
place to solder the fine wires.

It sounds like you have a bad L33 or one end that is not actually
soldered.  Make certain the tinned part of the very fine wire is
actually soldered to the lead of R116.
If it is well soldered, request a replacement L33 from
parts(at)elecraft(dot)com.

73,
Don W3FPR

On 12/4/2010 8:03 PM, kruegerbenny wrote:

> Hi,
>
> grounding of L33 doesn't bring the expected signal (7.xMHz). D37 seems to be
> mounted the right way (round caps in direction to front panel).
> If I put a resistor parallel to R116(it should be the right one:
> grn-brw-grn-(gold)), i get the 4.9MHz oscillation, but still no signal at
> TP2 (in this case, i get the following frequencies by contacting the int.
> probe to U11-P7: 4918.75 and 4916.12).
>
>

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[kruegerbenny]

Today I ordered a new L33 and X3/X4, will write as soon as they arrived ...

At this point: thank you Don for your indefatigable help!

Benny