[Yaesu] FT-857 (not 857D or ND) 6m self-oscillation

[mikea]

I just bought a used FT-857. On all bands except 6m, it's a great
rig, if a little power-thirsty. Folks tell me how good I sound on HF, 
2m, and 70 cm, and I get great signal reports for CW in those bands,  
too.                                                                  

There's a little problem, though: on 6m SSB it wants to go into a
nasty off-band self-oscillation: I see power out hit the peg, the
display turns brightest red when set to meter SWR or power out, and
both forward and reflected power on my tuner's meters go to the peg.
This is at any power level whatsoever, with the antenna tuner set
to present SWR below 1.1. Similar things happen when I'm doing CW;
there's an initial flash of high power out or high SWR, after which
the output settles down for the rest of the dit or dah.

The antenna and tuner are good: a borrowed Icom 551D works just fine  
with the same tuner settings, and doesn't present the anomalies in    
power out and SWR.                                                    

Google searches lead me to believe that this is a known -- and solved 
-- problem, but don't indicate the solution. Does it involve sending  
the rig and some money to Yaesu, or is it something I can fix here at
the QTH with hacksaw and a ball-peen hammer?

Thanks in advance for the help. 

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin