Is this a common problem with Splus machines? I'm guessing that something is causing the R3 to blow? I blew 2 of them up now.
No! That is NOT a common problem.
I work with about 100 S+'s and have NEVER had to replace ANY resistors on the MB....
Once, a MB burned up, but that was because someone dropped something metal onto the board, and shorted out two traces.
When you pulled out the MB, was there anything UNDER the board shorting out the bottom?
You'll see a LOT of exposed solderin under there.
A coin getting underneath will cause havoc for sure.
Are any pins in the long headers bent and touching?
That R3 runs directly to Pin-7 of the J10 header.
The 1st pin is always the square pin in the headers...look underneath.
On top, it's mostly the downward white arrows.
J1, J2, and J3 have upward pointing arrows.
J4, J6, and J11 have sideways white arrows pointing to the 1st pin.
Are there any pins bent anywhere inside of the header housings?
It's rare but I've heard of the U1 X2404 memory chip shorting out and burning up a board.
I unsoldered one once and installed an 8-pin socket for that chip.