Le Blog-Notes d'Olivier

During last Christmas holiday, my desktop PC suddenly stopped working while I was busy with a video edit. Nothing would move. Only the front LED stayed up. Had to do some fixing and took it as an opportunity to upgrade the CPU while keeping as many components as possible from the original machine.

Introduction

Four years ago, I bought myself a new desktop computer. Next to my laptop and tablet, his main role would be to run Davinci Resolve under Windows 10. To hold up to this task, it had to be a strong powerhouse but still, as a hobby driver, it would have to stay in a reasonable budget. I chose a Lenovo Legion T5 with an AMD Ryzen7 and an nVidia RTX3070 graphics card.

Interesting specs for this machine were:

• System: Lenovo Legion T5 26AMR5 90RC006QMH
• CPU: AMD Ryzen7 3700X 3.6GHz
• RAM: 32GB Kingston Fury DDR4 3200MHz
• GPU: nVidia RTX3070 8GB RAM
• SSD: 1TB M.2 SSD

Along the years, this machine served well its purpose and the only modifications I made to the setup were to add storage (a 6TB SATA HDD, an extra SATA SSD and a second M.2 SSD) in the 3.5″ bays next to the power supply and on the motherboard.

Until that day of December, when it stopped working. The screen went black and the fans stopped.

Investigation

Two suspects were immediately identified (thanks to Perplexity.ai):

• the most likely was the power supply;
• the second target was the motherboard but this was considered unlikely.

Checking the power supply

Doing a power cycle by pulling out the power cord and back in and then pressing the Power button, nothing moved.

Next step, removing the P8 connector (the one close to the CPU) and trying again powering up the machine, the fans spun up on the motherboard and on the GPU. Measuring the power delivered by the P8 connector, no voltage was found (instead of the expected 12V). This seemed to confirm the suspicion.

As a final confirmation, let’s try the paper clip test: put a paper clip between two specific pins of the P1 connector and see if the power supply starts and delivers power. This test failed, confirming the assumption.

So I looked for a new power supply. The original power supply used in the Legion housing is a 550W Huntkey block (SP50H29609). Since this is a standard micro ATX power supply, any standard block should work. I ordered a beQuiet! Pure Power 13M 750W. This one nicely replaced the original block.

But it wasn’t the power supply after all

Unfortunately this was not sufficient. After replacing the power supply, pushing the Power button, the fan briefly moved and a noticeable smell of electric fire. Unsurprisingly, the advice of the AI agent was « don’t try again ». The power regulators that convert the 12V from the P8 connector to the 1.4V required by the CPU are dead and create a straight short-circuit. Measuring the resistance of the pairs on the P8 connector of the motherboard confirmed the short-circuit.

Fortunately the power supply saw the short circuit and stopped immediately ensuring it wasn’t damaged. Maybe the Huntkey wasn’t that smart ?

So the motherboard is dead. A replacement needs to be found.

Selecting a new motherboard

The Legion T5 desktop uses a standard micro ATX form factor. Keeping that format ensures that it will be accepted in that box.

Happy with the performance of the Ryzen processor, I wanted to keep using this architecture, but possibly a more recent member of the family.

Since the original machine used a Ryzen7 on an AM4 socket, changing the socket format would imply a change of the memory, something I wanted to avoid. Indeed, the original AM4 motherboard used DDR4 memory and AM5 motherboards require DDR5 memory. So the choice is restricted to processors on AM4 sockets.

Next criteria was the compatibility with the peripherals present in the Legion machine: the nVidia GPU and the storage. In particular, it means that the motherboard had to have 2 M.2 slots.

Using AI to get proper suggestions, the choice was made for a MSI B550 Pro-VDH WIFI motherboard, to be furnished with a Ryzen7 5800XT Wraith Prism.

As I didn’t know that the processor would be delivered with a fan, I also selected a beQuiet! Pure Rock 3 to cool down. My « AI friend » wouldn’t trust the tower fan provided by AMD (Wraith Prism) and advised me to use the cooler from beQuiet! for maximum performance. Still, I was worried about the size of this piece (almost 16cm high). Would it fit in the Legion housing ?

How about internal connections ?

While waiting for the delivery of the components, I verified if and how to connect the peripherals included in the Legion box. For that, I compared the connections found in the Legion box, documented on their site, to the information given by MSI.

Immediately reusable

• the power supply is standard mATX, just connect P1 and P8 to the mother board and the PCIe power supply to the GPU board;
• the dual USB port on the front bezel are connected using a standard dual USB3 port (5Gbps), it goes straight in JUSB2 (cable is a bit short but it is usable);
• the motherboard offers 2 M.2 slots and 4 SATA ports:
  • M2_1 is the highest performance and should receive the 1TB system drive under the heatsink,
  • M2_2 is only a Gen3 port (same as in the original motherboard) and should receive the other SSD.
• Front and back fans are directly reusable, connecting the front to SYS_FAN2 and the back to SYS_FAN3;
• the backpanel delivered with the new motherboard can be installed in place of the Lenovo back panel (just push the original panel out and push in the new one).

Easily adaptable

More complicated

The front panel audio connections go to a 14-1 pin header on the original motherboard (F_AUDIO connector). The equivalent on the MSI board is JAUD1 which is a 10-1 pin header. An adaptation is required. As there is no definitive schematics of that adapted connection, I ordered an adapter from AliExpress (search for « Lenovo 13-to-9 female-male Front panel sound »).

I’ll add schematics when I get the adapter cable…

Not reusable

The thermal sensor that is hidden in the front bezel of the Legion box (connecting to a 6 pin header with white, red and 2 black wires in THER_HD connector #21) is of no use to the MSI motherboard.

The antenna wires and the WIFI board from the original machine are not reused. The new board has WIFI with two external antennas. The cables can be removed if you remove the terminations hidden in one of the bottom feet and in the front bezel.

Installation

Installation was really easy. It is always a bit of a stressing experience but all in all, everything fits in place.

There is just enough available height to install the beQuiet! Pure Rock 3 without touching the side panel. The air flow goes from front to back so the fan on the Pure Rock on the front side of the radiator, close to the DIMM sockets. I confirmed the direction of the air flow by forcing SYS_FAN2 and SYS_FAN3 at max speed and confirm it sucks from the front panel and blows out of the back of the case.

Remembering past experiences, I was afraid of the misery of adjusting the Windows installation to the new motherboard peripherals. I was surprised to discover that Windows 10 detected the new motherboard, installed automatically appropriate drivers and rebooted after a couple of minutes. I was advised to install MSI utilities and drivers. After a second reboot, it was ready to work.

By default, fans are working in DC mode so they run at full speed. Just go to the BIOS and set them up in PWM mode to allow control of the speed. By default, the fan speed curves are extremely careful. Much more than what is really needed with 3x 12cm fans. So I readjusted the curves in the BIOS:

About the tools from MSI, I already removed AIDA64 (useless trial diagnostic tool) and CPUID. I kept only MSI center but disabled auto-start.

I still have to restore Linux grub since that has been disabled by Windows when it restarted.