Sounds like you have "lost" the 8 volts you need for the Clarifier on LSB.
So, an easy check would be to see if the Clarifier pot itself - measure the same voltages across all its leads when in AM or USB or LSB.
IF the voltages are the SAME for every mode off the Clarifier header on the main PCB - then we have to think about a steering diode make have blown open.
Else if any of the voltages show a dip - then think about it this way:
The power that goes thru the clarifier is getting pulled down - but yet (or should) shows power at the Pot for it to work, then suspect you have a loading issue, which could be from a bad cap (unlikely for this case because the other modes would also load down this way) a bad header - shorted trace, or a blown diode showing shorted.
The Shorted diode would be in the MODE selector - but it can affect the Clarifier because you "lost" voltage from the clarifier pot - so the system can't power the oscillator unless you provide power for it - which sounds like what the clarifier is trying to do.
That may mean a blown diode in a PACKAGE - which is quite common -but you still have to get your ducks in a row first.
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I hope this information helps...
It could also be something as simple as a TX RX condition where the Fine Clarifier section is adding to the mess by still getting power - which if the unlock was done right would always be there for it but you wouldn't have TX power getting shoved in there 2X bypassing the Fine altogether.
Just some things to think about...
