It sure looks like an ATX mobo, from this ebay pic
I did find a service manual and it has a strange proprietary PSU layout... PCV-RXP-RZP System Reference Manual The PSU replacement section for the PCV-RX series is just above the system board detail. Pages 67-68 shows it has a standard 20-pin ATX and 4-pin CPU connector so you can just get any case / PSU combo like this In-Win Z583T.J350BFU2AD 350W for just over $55 shipped I have used similiar ones they are pretty good quality and the 350w unit is not all that bad.
Probably the same price as getting a replacement PSU from sony
I'm pretty sure it's a Micro-ATX case. Let me fill you in on my experience with this unit. The unit I have is three to five years old.
After a year (bought new), the PSU went out. It actually caused a power outage in my home. I quicky figured out it was the PSU. The PSU shorted out. Since the unit was still under warranty I called Sony.
They had a tech out in a day or two to give me a new PSU. By the way, the PSU is proprietary.
All was well for a few months. Then the PSU went out again. This time Sony had me ship the unit to L.A. It took them about a week to fix it. Total turn around time was 10 days.
I begin searching the web about the PSU to this unit. What I learned is that a lot of them were failing. At one time Sony promised a free Clio to those whose PSU's went dead. I never got the Clio. Sony never sent it.
My unit uses a Intel CPU and an ASUS micro-ATX mobo. My daughter's using the unit at college. No problems now for several years. If it dies again, I'll strip a few items and deep six the rest.
Besides the PSU problem, it's not a bad computer. However I won't buy a Sony again. I like to have something I can fix myself.
You are about to answer a thread that has been inactive for more than 6 months. If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.