Do them happen to be CECH-25xx ?
These units have a problem that causes the GPU to start drawing too much current (and overheating) and the only fix is replace the actual GPU. They shutdown with thermal incident (overheat).
Also it's possible that the thermal sensor might have malfunctioned. But if you had a transistor or resistor blow on the voltage converting stage it's very likely the GPU is in process of shorting out. Only permanent fix is replace the GPU chip completely.
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)