#1 Motherboard D-X79 PLUS No video, missing "VCORE" power supply
von matic • 28 September 2020, 23:17
Motherboard: D-X79 PLUS V2.0 (D-X79PLUSV2.0)
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Hello!
I'm working on the mentioned PC motherboard.
Issue:
The board respond to pressing on the power button and stay turned on, but there is no video.
The voltages are present on all coils, except the highlighted six coils near the CPU (picture below). The outputs of all six coils are connected together, so it is a 6-phase power supply. I assume it is a "VCORE" power rail.
If I turn on the board without a Graphic card connected, it turns on for about 5 seconds, then turns off and restarts automatically. Such a "restart loop" lasts all the time until I hold down the power button to turn off the board.
Interesting is that at every restart the voltage 1,1V appears on all mentioned six coils, but only for a very short time (26ms) and then disappears.
I checked the switching signals on inputs of all six coils with oscilloscope and all of them appears for a short time, so all six phases are working.
With connected Graphic card the voltage on these coils does not appear even for a short time when I turn on the board.
Resistance to ground on these coils:
- With CPU: 3,3Ω
- Without CPU: ~1,5MΩ
RTC battery is good (the voltage on it is 3,1V).
What I've done up to now:
- CMOS rest,
- RAM replaced with another known working one,
- I tried with a few different known working Graphic cards,
- CPU replaced with another known working one,
- BIOS chip reflashed with a dump from the Vinafix site
- CPU power supply controller chip uP1618A replaced with a brand new one
Any idea?
*******************************************************
Hello!
I'm working on the mentioned PC motherboard.
Issue:
The board respond to pressing on the power button and stay turned on, but there is no video.
The voltages are present on all coils, except the highlighted six coils near the CPU (picture below). The outputs of all six coils are connected together, so it is a 6-phase power supply. I assume it is a "VCORE" power rail.
If I turn on the board without a Graphic card connected, it turns on for about 5 seconds, then turns off and restarts automatically. Such a "restart loop" lasts all the time until I hold down the power button to turn off the board.
Interesting is that at every restart the voltage 1,1V appears on all mentioned six coils, but only for a very short time (26ms) and then disappears.
I checked the switching signals on inputs of all six coils with oscilloscope and all of them appears for a short time, so all six phases are working.
With connected Graphic card the voltage on these coils does not appear even for a short time when I turn on the board.
Resistance to ground on these coils:
- With CPU: 3,3Ω
- Without CPU: ~1,5MΩ
RTC battery is good (the voltage on it is 3,1V).
What I've done up to now:
- CMOS rest,
- RAM replaced with another known working one,
- I tried with a few different known working Graphic cards,
- CPU replaced with another known working one,
- BIOS chip reflashed with a dump from the Vinafix site
- CPU power supply controller chip uP1618A replaced with a brand new one
Any idea?
