[Elecraft] SSB Tx Problem

[Marinos Markomanolakis, M.D.]

Season's greetings to all,

Well I was thinking that my building experience would be uneventful, after 
successful completion and testing of the basic K2, but after the 
installation of the SSB adapter a problem showed up:
First, after installing the SSB board everything seemed fine and the Rx 
filters sounded fine, also did the carrier balance alignment as per the 
manual (using the K2 S-meter reading) which was fine too.

BUT when I connected a Yaesu mic (and another one acted the same) after 
properly configuring the connector at the front panel board), no Tx output.

The K2 goes into Tx mode, Rx muted and the power consumption goes from 240mA 
in Rx to 440-460mA in Tx but there is absolutely no power out when speaking 
on the mic at any preset power level. Activating the TUNE option does 
produce normal RF out just as before.
Did inspect the SSB, Control and Front panel boards for soldering problems 
and found none.
Finally did the voltage testing and it seems that most of my measured 
voltages on the SSB board are slightly lower than expected, for example 
U1pin9 on TX has 1.08V instead of 2.3V required, with other measurements 
being significantly lower:

             Rx (required)                    Tx (required)
U1-21     5.6 (5.8)                          0.1(0.02)
U1-22     0.13(0.2)                         0.0(0.0)
U1-25     0.0(0.0)                           0.65(0.8-1.2)
U1-28     5.6(5.6)                           5.47(2.4) !!!!!

U2-5       0.47(0.6)                         0.6(0.6)
U2-8       5.98(6.0)                         3.06(5.4) !!!

U3-4       1.4(1.7)                           1.7(1.7)
U3-5       0.2(0.4)                           0.4(0.4)
U3-6       0.0(0.0)                           0.6(0.8-1.2)

The above are the most abnormal values, from which I have put exclamation 
marks at the larger discrepancy values, the first one being the AUX-BUS 
U1-28 pin of the microcontroller. I tend to think that there lies the sourse 
of the problem, but have not been able to proceed any further with my 
diagnostics...

Saw some similar postings at the reflector which have been traced to bad 
solder joints or not removal of the required jumpers from the RF board 
before installation, but unfortunately, that does not seem to be the problem 
in my case...

Anyone has any ideas?    I do have a 40Mhz oscilloscope available, but it 
seems that this problem might be related to microcontroler communication 
rather than AF signal loss.

73,
Marinos, ki4gin.