CPU vcore missing in HP workstation Z2 Mini 4G

[Francisco.s]

Hi, have a HP workstation Z2 Mini 4G for repair with CPU vcore missing.

The resistance at the output of CPU vcore coils, is less than one ohm so I think CPU could be damaged, but no mosfet are damaged.
It mounts an i7 8th gen, and have only i5 7th gen for test, but I think it is not compatible.

Without CPU in the socket there is no short, but there is no vcore voltag, and it emits a beep like no detecting ram.

The controller chip for cpu vcore is a MP2949A, and has no enable voltage at pin 37.

I wonder which circuit generates this enable voltage, but 1.2v for ddr4 is present.

Do you know if there is a schematic from other motherboard that can help to make a diagnosis for this board?

[DynaxSC]

1. Check whether CPU VRM chip gets his power supply, VCC -> some serial usually 2.2 Ohms resistor may be burned.

2. Check whether CPU VRM get his ENable signal.

3. Does the board start w/o CPU at all?

If not look for SIO pin with Socket Occupied (Socc_Occ or something similar) signal and short it to ground, cheating the board there is a CPU mounted. Then start the board and see if you get VCORE.

4. Measure the PCH-CPU DMI bus in the CPU socket with diode setting on multimeter but reversed probes (plus probe to ground) - you should get on each pin some 0.2-0.3 V. If DMI bus is not OK, no VCORE will be established (Chipset negotiates with CPU and CPU VRM the power supply parameters by the Bios firmware).