[Boatanchors] TR-7 Digital Display Is Intermittent ???

[w0ng at comcast.net]

As a long time ham but first-time owner of a TR-7 (and new to this 
list) I'm hoping one of you veteran TR-7 folks might be able to tell me 
why my otherwise fine working TR-7 (built in Feb 1980) looses it's DR-7 
digital display after the rig is on for an hour or so. When the digital 
display goes out, the rig is otherwise not affected. Everything else 
works fine just no digital display. 

Turning off the power to the rig and turning it back on does not 
restore the digital display. There is no obvious pattern as to when it 
goes out. Sometimes at power up it is out and other times after the rig 
is warmed-up is goes out. No smoke, no weird sounds, no loose 
connections, no outward signs of any kind that it is going out.

Any help someone could offer would be greatly appreciated. I don't yet 
have the skills to troubleshoot the DR-7 board (or any of the digital 
circuits) yet. I'm hoping it is a simple fix one of you has used 
before. Thanks in advance. 73, Bill, w0ng