I've identified no more than 16 possible states for indication of motherboard diagnostic states which can be indicated with only 4 single colour LEDs which is:
In sequence after power on not waking from standby to RAM:
For the CPU/PCH/video, a single failure code is indicated if any part of it fails e.g. for the PCH, the IRQ controller, timer etc.
- No power applied (all off)
- Power applied - no standby to RAM (one is on)
- Standby to RAM
In sequence after power on not waking from standby to RAM:
- Power supply rail(s) missing or out of tolerance (includes CPU +12V)
- Power supply protection shutdown (trap - also display before boot)
- Onboard DC-DC converter failure (includes CPU DC-DC converter)
- CPU failure
- BIOS checksum failure
- Platform Controller Hub (PCH) failure
- Memory failure
- Video system failure
- CPU fan failure
- CPU over temperature shutdown (trap - also display before boot)
- Invalid configuration/CMOS RAM battery failure/overclocking failure
- Boot failure
- Boot OK (all illuminated)
For the CPU/PCH/video, a single failure code is indicated if any part of it fails e.g. for the PCH, the IRQ controller, timer etc.
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