[Elecraft] 40 Meter Transmitter Alignment problems

[Bob - AG5Q]

Hi David,

The voltages at the base and emitter of Q6 are inconsistent.  Since the
emitter goes to ground through a small resistor, R50, the base must be about
0.7 V more positive to turn Q6 on. This inconsistency may be caused by the
voltmeter probe affecting the operation of Q50, so when you measure the base
you see one thing and when you measure the emitter, the operation is
different so the two values don't seem to jibe.  It might also be caused by
the RF signal affecting the input circuitry of your meter, which expects a
DC input.  Rectification inside the meter can cause incorrect readings.

Take a 1/4W resistor in the range of 10K to 20K (the value is  not
critical). Wrap one lead of the resistor tightly around the voltmeter probe
tip and trim the other end of the resistor to about 1/2 inch long. This
isolates the stray capacity of the voltmeter from the point you're
measuring. Probe the base and emitter of Q6 with the resistor lead and see
if the readings are different from before.

The very low voltages at the collectors of Q7 and Q8 may indicate a problem
in the T3 circuit. Trace the voltage from the point where +12V enters the
circuit (in the vicinity of RFC4), through all the pads that the windings of
T3 connect to to see where the +12 gets lost.  Always use the isolation
resistor with your voltmeter when measuring points where there may be an RF
signal.

73/ Bob - AG5Q



----- Original Message -----
From: <david-davis@att.net>
To: <elecraft@mailman.qth.net>
Sent: Wednesday, January 01, 2003 12:59 PM
Subject: [Elecraft] 40 Meter Transmitter Alignment problems


> Hello All:
>
> This is an update to a post I made the other day.  I am trying to perform
the
> 40 meter transmitter alignment.  When I get to the portion of the
alignment
> that tells me to put the radio in <TUNE> mode and activate the build in
watt
> meter.  I try to adjust L1 for maximum output but the power level stays at
0.1W.
>
>
> I went through the troubleshooting section of the manual and made the
requested
> voltage checks.  I made all the measurements using two different meters
just in
> case one meter was bad.  The only one that was way off was D9 the expected
> measurement was 2.0 VDC and I measured .010 VDC.  I started to think that
Q7
> and or Q8 were bad because I did not get the proper measurements when
checking
> the transistors.  But WA7SPY had a spare set and we tested those and got
> similar readings.
>
> I then started looking through the scamatics and tested the transmit
voltage
> measurements for Q5, Q6 and Q10 as listed in the DC voltage tables.  The
> following resulted:
>
>
> Q5 :  B = 1.1 VDC expected 1.3 VDC,  C = 12.6 VDC expected 12.4 VDC,  E =
.515
> VDC expected .6 VDC
>
> Q6 :  B = .6 VDC expected 1.1 VDC,  C = 13.4 VDC expected 13.3 VDC,  E =
220.1
> mV DC expected .4 VDC
>
> Q10 :  D = 1.57 VDC expected 1.6 VDC,  G = 7.4 VDC expected 8.1 VDC,  S =
.95
> VDC expected 1.6 VDC
>
> In summary it appears that I have good voltages from Q5 B,C,E and good
voltages
> at Q10 D,G, and S but the base and emitter from Q6 are way down from the
> expected voltages.
>
>
> I have checked the winding counts for T1 and T2 and they seem to be wound
> correct.  I checked to see if I had an open through T1 or T1 but they seem
good.
>
> Does anybody have any suggestions where I should go from here?  Am I even
on
> the correct path?  Any help would be greatly appreciated.
>
> Thanks
> David Davis, KG6MTI
> david-davis@att.net
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