RAM-based BSODs but RAM tests fine

[Quartz]

I've been getting BSODs recently, all seeming to point to memory. Memory Management (0x1a) was the last one, and the most common. Others are Attempted To Write To Read-Only Memory (0xbe), Driver Overran Stack Buffer (0xF7), Kernel Data Image Error (0x7a). But the RAM tests fine.

I've had three crashes on one day and then the system behaved perfectly for nearly a week.

Or is this more likely a CPU error?

 

[Quartz]

I use Prime95. It picks up errors that pass Memtest. It also exercises the CPU.

 

[Quartz]

I fixed something similar a few weeks ago by switching the PSU with one from another machine.

Hmm... that's interesting. I recently disconnected my PC from the UPS because the battery died. A replacement battery is on the way.