HD4870 LEDs D1601 - Red LED On, shows critical temperature fault
D1602 - Red LED On, shows External power connector A was removed
D1603 - Red LED On, shows External power connector B was removed
D601 - Red LED On, shows critical Core power fault
At BOOT/POST, the card's fan will spin @ 100% for a short while and 3 of the 4 LEDs will light up for a brief period and then go out ( D601 should remain unlit ). This is NORMAL behaviour as the card is performing it's own type of POST test.
Courtasy from Gr33nGecko @
www.vgaforum.com DIAGNOSTIC LEDs ON HD4850/70 & HD4870X2
So basically if the LED's flash then go out every thing is fine. It's just the graphic card performing it's POST test.