Harvey, et al,
After going through considerable testing and reviewing a lot of marvelous advice and help from the group, I have come to an interim solution and am putting this problem to bed -- perhaps to research on a rainy day.
The problem was the overheating relays but I could not find the reason for the overheating except that possibly ALL the relays were defective. (Which I doubt.) If there was some deep-seated problem other than that, I'll look at it later. Meantime other projects awaited.
From the previous posts on this you will note that I discovered that cooling the plug-in board allowed it to operate hours on end without faulting on the display. So, succinctly, I was able to locate a source of 12 VDC (from the other existing fan board) and bolted in a three inch muffin fan I had lying around.
The burn-in testing with all covers and running in a "normal" environment failed to fail, if you will. It ran for eight hours. In fact, I ran BOTH of the frequency counter plug-ins I had -- the 7D14 and 7D15 -- in the same unit and was counting input signals to beat the band.
The link below is to my blog which contains pictures for any who would find that beneficial
Thank you all for your time, patience, and considerable help!
--
William, k6whp
"A friend told me to cheer up, things could be worse.
So I cheered up and, sure enough, things got worse!"
k6whp