Sadly Bruce, the PS/2 5V board can fail right out of the box, especially if it's 18-20 years old. There's no reliable gauge of when or if the board will fail. I've had some that failed with very low hours, and others that have over 1,000 hours on the clock still running fine.
Yes Joe, the 3V boards aren't perfect, but there's a number of factors in play.
- #1, they're way more reliable than the 5V boards.
- #2, they can be separated and many more components can be replaced if they do fail.
- #3, they are newer than the 5V boards, so stuff like electrolytic capacitors that dry out in time have more life left.
With the 5V board, I closely examine the 330uf capacitor near the edge of the board, it's the largest cap on the board. For whatever reason, I've had an inordinate number of failures of that part. If I see ANY signs of bulging or leaking, or it's the WINCAP brand, I replace it immediately! It's a difficult fix, but with a fine tip soldering iron and by prying the boards partially apart, I can replace it. Of the twenty-odd dead boards in my 5V graveyard, over half had signs of that capacitor leaking, and all but one of the leaking capacitors was the WINCAP brand. That's enough evidence for me to suspect that particular capacitor brand.
Obviously, to replace the 330uf cap, the easier issue is getting the old one off, I just chop it up and then remove it's leads from the PCB. The tricky part is getting under the sandwiched PCB's to solder the new one in place.