[Kenwood] TR-751A problem

[Al]

Have acquired from estate the two meter multimode TR751A which works 
properly except for a squelch problem.  When the radio is first turned 
on there is just a few seconds of unsquelched noise (any mode) then the 
squelch is tight.  No sigs get through and the control has no effect. 
The S meter indicates receiving sigs but RX dead due to squelch.  All 
other functions (xmt, memory, etc) appear fine.  Any suggestions?
Al K7IEY