Remember, you said you checked TR31 already. It's the selector that routes - that when you're in AM mode, aka the BASE is on in AM mode, which if it has power from TX MODE (aka lock back to TR35 and the MB3756) R112, R113 and TR21 Base shows voltage - they will show 3.7 to 5V. D41 shows power 5V ~ 7V - R150 shows power and you get 7.8MHz on X4
When not in TX mode - what is NOT supposed to have power IN AM MODE - is TR31 - so that kills TR21 power AND D41 - no power in RX Mode.
One thing I'm seeing and I'm trying to tell you this, and you're frustrated - by what was posted... you seem to have EXTRA power from somewhere still sending - to where? Not sure. It is acting like your RX IF for AM mode is still on no matter what mode - which brings us back to TR31 because of it's "AND" functions. It turns on AM 7.8MHz ONLY FOR TX - not RX. So D41 should be off in RX but ON in TX.
The AND diodes (power steering) are D36 (LSB) , D37 (USB) and D38 - BUT D38 has a CONDITION that is set on it's UNBANDED SIDE - It SHOWS NO POWER IN AM MODE ONLY IN TX.
What I'm trying to lead you to, is the 7.1MHz IF in AM. Is that sending/working? That power routing seems to be skewing your readings. That takes me back to TR33 - AM mode RX - but only in AM Mode, It's that darn IF 2nd conversion stuff that is making this harder to track down.
And you say Receive for SSB is attenuated, or lower - that is on Pin 4 of the TA7222P - it's the audio pin that turns off using TR53 when the PLL is out of lock - it can't do that if the cap that it uses - to suck all the power off the audio line - C232 2.2uF - is bad or TR53 is not on when the PLL fails to lock - hence TR33 and TR47 work together to power TR53.
Pin 6 of the PLL should be +6V or so when in lock - D31 makes this directional - as in, when it's out of lock, it sinks current INTO the PLL there is a pull up resistor of 22K (R163 off of Pin 1 PLL power) on the line back at the PLL to "float" the line about 2.V or less - just nothing that goes below 0V or above 8V so it doesn't go poof...and helps in recovery.
Then there is a major fail mode, the channel selector does that - it GROUNDS the line all the way to zero if it works right.
There is a DETENT on the channel selector switch, that CLOSES when the detent is not set right - this helps the PLL FORCE DOWN and NEGATE the effects of R163 pull up. It sets this line LOW (knob not set right) and turns ON TR47 (grounds base lead it's a PNP) thru it to TR53 (NPN via splitter R223 and R224 off of TR33) to mute Pin 4 of audio chip and OFF TR35 (an NPN) It sets ground, pulling power off the line, turning off the TR35 and PREVENTS MB3756 toggle RX and TX - while keeping 8 volts available for mode selector - back to TR33 (NPN) being told to stay on if in AM mode. Just TR35 keeps TX from working while the BASE, Pin 6 of the PLL or the channel selector DETENT are LOW.and reserve power from TR33 goes thru into the splitter and into TR47 to turn on TR53 as a mute.
So, does the channel selector seem to work ok? Does Pin 6 at the PLL float at 2V or less, seems to (1.3) so the PLL out of lock signal means it's not getting something right. and only in specific areas - so perhaps the Channels "programming" is not right - hence that special pin getting special treatment.
WHEW
:+> Andy <+:
