[Elecraft] (no subject)

[John Wiener]

If this is not appropriate, please let me know.

A am forwarding this to the group in the hopes of getting some  
additional help and to perhaps decrease Gary's load a bit.
I am not getting any significant output from my K2 in Alignment III.   
I've replaced Q7 and Q8 (broke the leads), rechecked T1-T4 and  
resoldered.  Found some missing parts and corrected.

I'm hoping there's something OBVIOUS I'm missing.

John
AB8WH

=

Gary

Here are the (partial) results.  I'm afraid I really don't have the  
BIG PICTURE

When using the RF probe, my DVM is set to VDC
On May 22, 2006, at 8:19 PM, Gary Surrency wrote:
The PA transistors should be OK as long as you did not transmit with  
the PA heat sink removed, and none of the leads are broken off.  
Always replace both PA transistors at the same time if one of them  
fails, overheats, or stays cold during transmit, or fails the base  
bias test of 0VDC in receive, not more than 0.62 to 0.65VDC in transmit.
0 VDC in Receive...3 mV in Tx
Both PA transistors should get warm around their mounting hardware on  
the heat sink after a few seconds in transmit, and both need to be  
healthy in order operate properly in the push-pull PA stage.
  They feel a little warm after about 10sec
Q22 is supposed to be warm after the rig has been on for a while. It  
is NOT associated with transmitting - only with receiving.

Lack of RF output on all bands usually means the PAs are damaged, or  
there is a problem with some of the parts around Q5-Q8, T1-T4. Doing  
RF voltage tests is the best way to narrow down where  the problem is:

Here are useful measurements to take when the rig is in transmit.

All measurements taken at 7100kHz with a 100MHz oscilloscope, at  
maximum TX output unless otherwise specified.


anode side of D7        220mVpp      In TX, D7 has 8.11 VDC on its anode

about 220 mv on RF      7.88 VDC
cathode side of D7      200mVpp      In TX, D7 has 7.49 VDC on its  
cathode

about 200 mv on RF	7.25 VDC
jumper W6               250mVpp      Note: L1 and L2 *must be peaked,  
or you will not get this.

.360  V on RF
collector of Q5         500-600mVpp  Q6 has 12.58 VDC at minimum  
output, 11.9 VDC at full drive

How can I measure Leads of Q5 when I need to remove sink to access?

base of Q6              200mVpp    Near sine wave. 800mVDC to 1.1VDC

160 mV

collector of Q6         6-10Vpp    Nice sine wave. 13.6-12.5VDC, 0.1  
to 15W out.

3.3 V

base of Q7/Q8           2Vpp       some distortion is normal here.  
0.620 to 0.650 VDC


Q7 .62   Q8 .65  VDC		RF  probe: .03 V and dropping over time
collector of Q7/Q8      21-25Vpp   also distorted here at full power.  
13.6 VDC

8 to 8.5 VDC
jumper W1               70-80Vpp   clean sine wave

40V
antenna jack            70-80Vpp   clean sine wave

mVpp = RF millivolts peak to peak

Vpp = RF volts peak to peak

NOTE:  The RF probe in the kit will show only about 35% of these pk- 
pk voltages as it reads rms voltage, not peak to peak.

Do not use the probe on the antenna RF output or the diode detector  
in it may be damaged.

I hope this info helps you to track down where the problem is.

--
73, Gary AB7MY
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