MSI Z390-A PRO missing VCORE voltages

[karlp028]

I've got an MSI Z390-A Pro motherboard that starts up fine, but it's missing the VCORE (and VGT) voltages. All of the other voltages are present (e.g. VCCSA, VCCIO) and I know the CPU (i7-9700k) is good. Now, the original PWM controller (UP9521P) had an internal short and I replaced it with a new one. All of the enable signals look good. The problem seems to be the PWM signals going to the MOSFET drivers. I checked them with an oscilloscope and they are all flat 1.5V with no pulses. I don't know why this would be and I'm not sure where to look next.

[karlp028]

I did a little more digging, but didn't get much farther. I checked all of the signals in this startup sequence and they are all good.

I also did a capture on the SVID data line and there is a whole bunch of stuff there. But, I don't think I have any hope of deciphering that.

I'm not sure where to look next.

[Much Bugs]

You should check the operating conditions of the controller IC and BUCK IC to see if they're satisfied. The PWM voltage is a steady 1.5V, so it looks like the PWM output of the control IC is set to high-impedance tri-state or mid-state , and the BUCK IC will be in standby mode in this case. At least that's how it is with MPS ICs. Here are MSI Z390 A-PRO Schemetaic and BoardView Files :

[SMDFlea]

You should check the operating conditions of the controller IC and BUCK IC to see if they're satisfied. The PWM voltage is a steady 1.5V, so it looks like the PWM output of the control IC is set to high-impedance tri-state or mid-state , and the BUCK IC will be in standby mode in this case. At least that's how it is with MPS ICs. Here are MSI Z390 A-PRO Schemetaic and BoardView Files :

Please post the schematics and boardviews in this existing request topic where everyone can find them https://www.badcaps.net/forum/troubl...atic-boardview

[Much Bugs]

If you need those shematic and boardview files , then here they are : MSI Z390 A-PRO Schematic and BoardView - Badcaps .🧐

[karlp028]

You should check the operating conditions of the controller IC and BUCK IC to see if they're satisfied.

The operating conditions of both are fine. The supply voltages are well within range.

I suppose the PWM chip could be bad. I do have another one, but I want to explore further before I replace it.

[DynaxSC]

Short J1 jumper and start board. J1 will normally force vcore to rise. If it does not start then there is an hardware issue with the vrm network. MSI boards usually have such test jumper, good idea by MSI, other vendors unfortunately do not implement this.

Check whether the buck IC is correctly soldered in, these IC's tend to get some pins not connected correctly when replacing. I personally after replacing always go around with a thin solder iron from all sides to go sure all pads/pins are correctly tinned.

Check whether buck controller gets EN signal.

Measure the gates of the mosfets if they have normal resistances (must not all be same, but in range of 10-100 kohms, sometimes Mohms).

Measure low ohm resistors in the vrm network for discontinuity or decalibration.

Check whether RAM's get 0,6V and 1,2V powers, vcore will not start before RAM is fully powered.

[karlp028]

The oscilloscope I was using is just a cheap portable one and it's not very accurate. I was playing around with it more and it actually looks like there are valid PWM signals, although the voltage is too low to trigger the MOSFET drivers.

[karlp028]

Short J1 jumper and start board. J1 will normally force vcore to rise. If it does not start then there is an hardware issue with the vrm network. MSI boards usually have such test jumper, good idea by MSI, other vendors unfortunately do not implement this.

When J1 is shorted I do get 1.05V for VCORE. I guess that means there is some issue with the SVID handshake between the VRM controller and the CPU when J1 is left open? I tested this CPU (i7-9700k) in another system so I know it works.

In any case, the CPU debug light is still on and there is no display output.

[karlp028]

I just noticed that someone replaced the stock BIOS chip, Winbond W25Q128JV, with a Macronix MX25L12872F. I'm assuming they are not compatible, so, that could be contributing to the problem.

[DynaxSC]

Only if chip supply voltage is different (1.8V vs. 3,3V), otherwise the common SPI chips with same capacity are quite compatible and can be replaced.
You can use the scope on eg. data pin 2 of the chip, to look if after Reset or Power On the PCH reads the SPI chip, this should be visible if you set a very slow time range on the scope. There should be some short signal groups from H to L visible.
Otherwise if you have access to a 1:10 low capacity scope probe you also can check whether the clocks of the PCH are working - this can be measured on the hot pins of the crystals connected to some few picofarad (10-15 pF) caps.
The probe must be set to divide the signal 1:10 to make the parasitic capacity as low as possible, otherwise the crystal will stop to oscillate. Scope must be on the other hand set to a quite high voltage sensitivity, as the clock signal is very low amplitude. I have seen PCH's which did not generate one or both of the clock signals due to aging and silicon degradation. If so, sometimes exchanging the crystals and/or the pF caps for slightly higher/lower capacity helps.
Further I would backup the BIOS image and program a stock image to test if BIOS image is OK. Sometimes corrupted BIOS images prevent board from POST-ing. Also there are some "inventors" who exchange the BIOS images to ones from different board models (eg. Z490 to Z590) to have more options available, so it might be that your image is an alien one.

[karlp028]

Now here's something strange. I used a CH341A to flash the latest stock BIOS and verified it (twice). After feeding standby power to the board for a few minutes to check some voltages, I decided to verify the BIOS again. It had changed and the hash no longer matched the stock image. I repeated this a couple more times and it was always the same issue. I can't imagine how this is happening.

[karlp028]

Nevermind that last message. I don't know what I'm talking about, LOL.

[DynaxSC]

I assume this is normal, as the PCH might write something into the SPI chip after power is applied to the board. The PCH and the SPI chip are both all the time powered, even in standby mode when the board is switched off, so it can alter contents of the SPI chip. As far as I remember there is always some short data exchange between SPI and PCH after application of the +5V standby voltage.