You've got exactly the same problem as I have on one of the PS3's I've got sitting downstairs.
In my thread, someone suggested replacing the thermal paste on the GPU. Apparently that sometimes works and sometimes doesn't. I'm considering a reflow as if it were a YLOD case to see if that fixes it, just haven't had time to do it yet.
EDIT: I just noticed you said the problem occured AFTER a reflow. Stick a HDD in it. The CECHC03 I have that had YLOD refused to do anything until I put it's HDD back.
60GB (120GB WD Scorpio Drive) PS3 (CECHA01, NTSC), 3.7OFW
60GB (640GB Samsung Drive) PS3 (CECHC04, PAL), Kmeaw 3.55, Repaired (Dead Laser)
PSP-1003 FAT, CFW5.00 M33-6 & Prometheus v2
X-Box 360 Xenon (JTAG'ed, 500GB HDD)