Dell OptiPlex 780 Service Manual - Page 15
Diagnostic Lights, Light Pattern, Problem Description, Suggested Resolution - video card
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3-4-3 4-2-1 4-2-2 4-2-3 4-2-4 4-3-1 4-3-3 4-3-4 4-4-1 4-4-2 4-4-3 4-4-4 Search for video ROM failure No timer tick Shutdown failure Gate A20 failure Unexpected interrupt in protected mode Memory failure above address 0FFFFh Timer-chip counter 2 failure Time-of-day clock stopped Serial or parallel port test failure Failure to decompress code to shadowed memory Math-coprocessor test failure Cache test failure Diagnostic Lights To help troubleshoot a problem, your computer has four lights labeled 1, 2, 3, and 4 on the bank panel. When the computer starts normally, the lights flash before turning off. If the computer malfunctions, the sequence of the lights help to identify the problem. NOTE: After the computer completes POST, all four lights turn off before booting to the operating system. Light Pattern Problem Description The computer is in a normal off condition or a possible pre-BIOS failure has occurred. Suggested Resolution Plug the computer into a working electrical outlet. If the problem persists, contact Dell. The diagnostic lights are not lit after the computer successfully boots to the operating system. A possible processor failure has occurred. Reseat the processor (see Processor information for your computer). If the problem persists, contact Dell. Memory modules are detected, but a memory failure has occurred. If two or more memory modules are installed, remove the modules, then reinstall one module and restart the computer. If the computer starts normally, continue to install additional memory modules (one at a time) until you have identified a faulty module or reinstalled all modules without error. If available, install working memory of the same type into your computer. If the problem persists, contact Dell. A possible graphics card failure has occurred. Reseat any installed graphics cards. If available, install a working graphics card into your computer. If the problem persists, contact Dell . A possible floppy drive or hard drive failure has occurred. A possible USB failure has occurred. Reseat all power and data cables. Reinstall all USB devices and check all cable connections.