Other questions was RE: K2 Alignment and Test, Part III: High current

[K.Kishimoto]

Hi Don and everyone else who responded,

The current readings @ 5W and 10W are now at the upper end of normal levels.
T4 was reversed and needed to be turned around. The power wire is also on
the thin side, 16g or 18g. I'll find a replacement tomorrow.

Two new interesting problems have cropped up as well:
a) 20m band, tuned Zepp: The S-meter is pegged on +40dB when the preamp is
on. With the preamp off,  the meter settles down to around S5 (S5-S9 when
copying a signal). On 40m, antenna tuned, the LED reads +40dB with preamp
and +20dB without. Tried following the S-meter setup instructions in the
manual, including those on the XG1 mini-kit, but nothing seems to prevent
the LED from locking into the upper limit when the preamp is on. Is this
normal? The AGC can be switched on and off as well as set fast or slow. With
AGC off, the S-meter drops to zero.

b) The gain drops intermittently from an S-meter reading of +40dB to S2 with
preamp on. The audio also diminishes in intensity at the same time. The last
time it did this, I tapped the left side of the radio a couple of times and
it stopped dropping out. This sounds like a loose component, bad connection
or bad solder joint. Where should I begin my search? The IF stage? Could it
be a toroid with a bad solder joint?

Thanks,
Kathy

> ------------------------------
>
> Message: 43
> Date: Sun, 25 Dec 2005 01:44:48 -0500
> From: "Don Wilhelm" <[hidden email]>
> Subject: RE: [Elecraft] K2 Alignment and Test, Part III: High current
> To: "K.Kishimoto" <[hidden email]>, <[hidden email]>
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Kathy,
>
> I suggest that you tackle the voltage drop problem before investigating
> the
> current draw.  What size wire are you using for the power wiring? - it
> should be 16 guage or larger.  Next check all the connections from the
> power
> supply to the K2 - they should be tight or well soldered.  If no problem
> is
> discovered in the power supply wiring itself, measure the voltage at the
> power supply output terminals under the load in transmit - compare to the
> K2
> display.  The K2 display should show about 0.3 volts less than the power
> supply output due to the protective series diode.
>
> Lastly, check the soldering in the K2 12 volt path to be certain there are
> no high resistance solder joints.
>
> Once you get the voltage drop under control, the current should fall in
> line
> with what is expected.  You receive current draw is about normal.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>> Power supply: SEC 1223 (23A)
>> Unit type: K2, no options installed
>> Passed Alignment and test, Part II
>> Passed all resistant checks
>>
>> Baseline voltage and current (backlight on)
>> 13.5v, 0.24A
>>
>> Transmit voltage and current into Elecraft 20W Dummy load (Using TUNE
>> function)
>> At 5W: 12.7v, 1.84A
>> At 10W: 12.1v, 2.98A
>>
>> The current draw seems far too excessive given the suggested range in the
>> manual. What components could potential cause this problem? The
>> voltage drop
>> seems high as well given the capacity of the PSU.
>>
>> Thanks,
>> Kathy
>> *Merry Christmas!*
>>

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[Don Wilhelm-3]

Kathy,

Great that you found the transmit problem - and if you can use larger wire
for the power supply, the voltage drop will be less and will likely reduce
your current draw on transmit a bit more.

Yes, your preamp dropout problem does sound like a bad solder connection is
the most likely cause.  Places to check are those components associated with
Q21 - look on the schematic (sheet 2) for the RF Board to identify those
associated components, and don't overlook pins 4 and 7 of relay K17 and
toriod T6.  Actually anything in the receive chain from the antenna through
the IF Amp will effect the AGC action (and subsequently the S-meter), but if
the S-meter appears normal with the Preamp off, then the problem is likely
confined to the preamp stage.

Solve the preamp problem first and then tackle the AGC - since your S-meter
seems close to normal with the preamp off, fixing the preamp may take care
of the S-meter anomoly too.  True the AGC (and S-meter) should not behave as
you describe, but you can optimize the AGC threshold after you know
everything else is working properly, then finally adjust the S-meter as the
last step.

73,
Don W3FPR

> -----Original Message-----
>
> Hi Don and everyone else who responded,
>
> The current readings @ 5W and 10W are now at the upper end of
> normal levels.
> T4 was reversed and needed to be turned around. The power wire is also on
> the thin side, 16g or 18g. I'll find a replacement tomorrow.
>
> Two new interesting problems have cropped up as well:
> a) 20m band, tuned Zepp: The S-meter is pegged on +40dB when the
> preamp is
> on. With the preamp off,  the meter settles down to around S5 (S5-S9 when
> copying a signal). On 40m, antenna tuned, the LED reads +40dB with preamp
> and +20dB without. Tried following the S-meter setup instructions in the
> manual, including those on the XG1 mini-kit, but nothing seems to prevent
> the LED from locking into the upper limit when the preamp is on. Is this
> normal? The AGC can be switched on and off as well as set fast or
> slow. With
> AGC off, the S-meter drops to zero.
>
> b) The gain drops intermittently from an S-meter reading of +40dB
> to S2 with
> preamp on. The audio also diminishes in intensity at the same
> time. The last
> time it did this, I tapped the left side of the radio a couple of
> times and
> it stopped dropping out. This sounds like a loose component, bad
> connection
> or bad solder joint. Where should I begin my search? The IF
> stage? Could it
> be a toroid with a bad solder joint?
>
> Thanks,
> Kathy
>

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[K.Kishimoto]

Hi Don,

I removed, checked, cleaned and reinserted T6 and T7. I also did a visual
check for bad joints around Q21.

I also did a side by side comparison with my FT-897 while listening in to a
LSB QSO on 40m. The same antenna was used and I switched between radios
using a B&W switch. Without the preamp on, the K2 exhibited better signal to
noise ratio than the FT-897 with the preamp running. The K2 preamp, when
engaged, amplified both noise and signal with no further improvement in
quality.

When the K2 preamp is switched in, the S-meter will jump from S1-S2 to +20dB
(on 20m, untuned antenna). This seems to be rather large and I'm wondering
if the preamp is working fine, but one of the other amps is faulty. I'm
going to give the IF and post-mixer amps a good look later today.

Thanks,
Kathy


----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "K.Kishimoto" <[hidden email]>; <[hidden email]>
Sent: Monday, December 26, 2005 3:20 PM
Subject: RE: Other questions was RE: [Elecraft] K2 Alignment and Test,Part
III: High current

> Kathy,
>
> Great that you found the transmit problem - and if you can use larger wire
> for the power supply, the voltage drop will be less and will likely reduce
> your current draw on transmit a bit more.
>
> Yes, your preamp dropout problem does sound like a bad solder connection
> is
> the most likely cause.  Places to check are those components associated
> with
> Q21 - look on the schematic (sheet 2) for the RF Board to identify those
> associated components, and don't overlook pins 4 and 7 of relay K17 and
> toriod T6.  Actually anything in the receive chain from the antenna
> through
> the IF Amp will effect the AGC action (and subsequently the S-meter), but
> if
> the S-meter appears normal with the Preamp off, then the problem is likely
> confined to the preamp stage.
>
> Solve the preamp problem first and then tackle the AGC - since your
> S-meter
> seems close to normal with the preamp off, fixing the preamp may take care
> of the S-meter anomoly too.  True the AGC (and S-meter) should not behave
> as
> you describe, but you can optimize the AGC threshold after you know
> everything else is working properly, then finally adjust the S-meter as
> the
> last step.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>> Hi Don and everyone else who responded,
>>
>> The current readings @ 5W and 10W are now at the upper end of
>> normal levels.
>> T4 was reversed and needed to be turned around. The power wire is also on
>> the thin side, 16g or 18g. I'll find a replacement tomorrow.
>>
>> Two new interesting problems have cropped up as well:
>> a) 20m band, tuned Zepp: The S-meter is pegged on +40dB when the
>> preamp is
>> on. With the preamp off,  the meter settles down to around S5 (S5-S9 when
>> copying a signal). On 40m, antenna tuned, the LED reads +40dB with preamp
>> and +20dB without. Tried following the S-meter setup instructions in the
>> manual, including those on the XG1 mini-kit, but nothing seems to prevent
>> the LED from locking into the upper limit when the preamp is on. Is this
>> normal? The AGC can be switched on and off as well as set fast or
>> slow. With
>> AGC off, the S-meter drops to zero.
>>
>> b) The gain drops intermittently from an S-meter reading of +40dB
>> to S2 with
>> preamp on. The audio also diminishes in intensity at the same
>> time. The last
>> time it did this, I tapped the left side of the radio a couple of
>> times and
>> it stopped dropping out. This sounds like a loose component, bad
>> connection
>> or bad solder joint. Where should I begin my search? The IF
>> stage? Could it
>> be a toroid with a bad solder joint?
>>
>> Thanks,
>> Kathy
>>
>
>

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[Gil Stacy]

Kathy,

The K2 does not need the preamp on 40 meters.
Ron D'Eau Claire wrote ion the list in  Nov of 2004 how to determine when
the preamp is used on the K2.  I quote from his post:

"The purpose of the preamp is to improve the noise figure on the
higher-frequency bands, not to make the receiver louder. It does that, of
course, but that's a secondary benefit. The issue is that the 'atmospheric'
or 'background' noise on the higher bands - usually above 15 MHz - can be so
low the internal noise in the K2 receiver could mask signals. The easiest
way to tell if that's true is to turn the preamp OFF, tune your K2 to an
empty frequency so all you hear is noise, set the IF filter for the
narrowest bandwidth you might use, and disconnect your antenna. If then
background noise level drops when you disconnect the antenna, you do *not*
need the preamp. The sensitivity of the K2 is entirely limited by the
background noise."

73, Gil NN4CW


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