[ICOM] IC 761 Problem

[WØQFC]

I am posting this for a friend, WA2KDB.
The rig has never had a problem before today:
After being on the air on 20 for several hours, the RX died. No signals 
received, but there was slight noise from the speaker.
Turned off rig and waited one hour. Worked for about ten seconds and then 
quit again as before.
After two - two and one half hours, the rig worked fine.
Any ideas on cause and what to look for?

TIA
All other bands worked ok.
Gene, WØQFC
Spring Hill, Florida
WEB SITE:
http://www.w0qfc.com