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

[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" <w3fpr at earthlink.net>
To: "K.Kishimoto" <mobileuser at shaw.ca>; <elecraft at mailman.qth.net>
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
>>
>
>