[Kenwood] TM-255A Power On Problems, New Question

[John O. Newell]

I'm wondering if anyone can help me follow up with suggestions on this problem.  My TM-255A has what seems to me an odd problem with powering on.  If the radio is used for a period of time, even if *only* on rx, and is turned off, it will not power up again until an extended period of time has passed...like overnight.  
I'm guessing that whatever is going on is somehow heat-related, but running the radio on rx only shouldn't build up much heat, and I'm not sure what circuit would be likely to be opening when heated then closing when cooled.  Since the radio operates fine when running, I'm guessing it's in the power switch or in the connection between the control head and the chassis -- but all connections here seem intact and secure.  The radio has never been used mobil.
Has anyone seen a TM-255 with this kind of issue?
Many tks for any assistance and 73s
John Newell KB1FPM