Very odd that you mentioned this because for some reason I have had Eric Clapton's Unplugged "Layla" song going in my head at random times throughout the week, although these days, I don't actively listen to music.
Back on track - rhb and peteb2 - I really appreciate your comments. I was kind of hoping to cease using this particular thread because I started a thread more specific to my needs,
https://www.eevblog.com/forum/repair/how-to-troubleshoot-your-defective-386486-motherboard-with-an-oscilloscope/ but it looks like I'll be reading on two fronts. I was actually hoping that the OP would have updated us on his/her progress, but I guess he/she has moved on.
In response to some comments, I am doing this strictly as a hobby. I used to to work as an engineer by profession and now have taken up collection of specific periods of computing history. I also setup systems around such hardware as a hobby. There is actually a fairly substantial following in this field of interest as of recent. e.g. you can check out the vintage computer forum,
http://www.vcfed.org/forum/forum.php , or Vogons at
http://www.vogons.org/ . The interest is mostly centred around vintage gaming on period-correct hardware, although there are others, like me, who don't game but are more into the hobby aspect of restoration and tinkering. 15-20 years ago, I could buy very high-end 1990's-era motherboards, CPUs, graphics cards, SCSI adapters, etc. on eBay for next to nothing. These same items today, if you can even find them, now sell on eBay in the hundreds of dollars. So aside from the hobby aspect of it, one may be able to reap substantial capital gains when selling. By way of example, back in 2003, I could buy a rare Cyrix 5x86-133/4x for $25. There was an eBay posting this year for this CPU, which only happens about every 5-10 years, and the bids were running north of $500 (although the reserve was never met). Just 6 years ago, you could buy a Voodoo 5 graphics card on eBay for $30. People are now paying $200+.
Another aspect of the hobby for me is that it brings me back to an age which I consider a golden era in computer history. I am personally fond of the 386-486 era, but my interest does extend into Tualatins, though the passion for me diminishes substantially.
The two dead boards I'm trying to get working are not for me. They are for a younger chap who seems to be developing a vintage computer fever. They are actually his boards. I have always enjoyed trying to repair old motherboards or computer hardware. Sometimes I give up, and stick the board in a box for a decade or more; then at a later point, when I have slowly accumulated more knowledge, I am often able to get them running again, though not always. This is a hobby and I enjoy learning and solving problems in the EE arena. My main limitation now is time and sleep. With 3 restless youngsters at home and a wife, my only time to tinker is the midnight hour and for a short duration. Tonight, looks like I'll only have time to read posts.
peteb2 - very interesting stories. Thank you for sharing. Sounds like that 486 pin was just barely making contact in its 90 degree bent position. Perhaps some mild corrosion or oxidation over time made the contact intermittent.
peteb2 - it is very likely that the boards of interest have been dropped. They were sitting around some community college waiting to be scrapped. Who knows how many static bodies rubbed all over them. The fact that the other two boards (the ones I got working) were contact issues makes me lean in the direction that the 2 dead boards may have similar issues, and as per your story, could be inner-layer contact issues.