The bug is not on the LA chip. It's on the Mechanics controller (MECHACON) firmware.
It controls the tracking coils through an interrupt routine or something similar and if the MECHACON freezes, the PS2 stops responding to the reset button, keeps the laser and focus/tracking coils on at maximum current. It just happens to be the tracking coils which fry first.
On some rare cases, both coils burn. And on some other cases (related to bad install of modchips) the DVD or CD laser emitter burns out.
It is actually designed to burn/fail that way. Because of possible fire hazards they asked Sanyo to add fuses on the outputs of the LA6507 chip.
The older ROHM chips used on earlier models (BA5810/5815) suffer of short circuit/major failure when such a crash happens, causing the 2amp fuse to blow and the console to stop displaying the screen (MECHACON detects that the console has a fault on the servo driver and does not reply to the ready request from the CPU/BIOS so the screen remains black and the system halts.)
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...)