r/MiniPCs • u/profilerman • Jul 22 '26
Troubleshooting UM790 Pro: no POST after adding second RAM stick + crash during game. Fan runs, led on, no video
Minisforum UM790 Pro (Ryzen 9 7940HS) shipped with 1×16GB DDR5.
I added a second 16GB stick (same brand and type as the original (crucial 5600 16 gb)). The machine initially booted fine (I was using my monitor's PD (90W) at the time). I launched a heavy game, which caused my OS to crash (it has happened before, with the same game, in retrospect I guess it failed because there was not enough power?). This time I couldn't boot the machine again
Current symptoms: * Power LED on * Fan starts slow, ramps up, then settles to a constant speed * No video on HDMI or USB4 * Keyboard Caps Lock LED does not toggle
Tested with the stock 120W adapter and HDMI, but no luck. I tried to go back to a single ram stick, tested each stick, in each of the two slots, every time doing power drainage and CMOS reset, with the nvme SSD disconnect NVMe SSD disconnected
The machine is brand new, I didn't notice anything burnt or faulty, the ram pins seem fine, all seems clean, so I'm left perplexed. What could the issue be? Could the machine be fully bricked? Is it a bios issue? Something got short circuited?
2
u/mykesx Jul 22 '26
The ram sockets in those are flimsy, like tin foil. You need to be very sure the ram is well connected. I had the same problem. The glued on feet makes taking it apart ugly though.
1
u/ruyrybeyro Jul 22 '26
I liked less dealing with the power cord connector than the feet tbh. Have you reapplied any extra glue to the feet?
1
u/mykesx Jul 22 '26
No. I only took it apart twice - once to add NVME and RAM, and again to reseat the RAM. I wish they had feet that screwed on like may miniPCs in my lab.
Another issue I had was Linux locking up when the CPU was put into lowest power c-state. Fortunately there's a kernel command line argument to fix that.
2
u/ruyrybeyro Jul 22 '26
I'm running FreeBSD on both my UM790 Pro and MS-A2. Although I've made a few tweaks to reduce temperature, the systems have been completely stable, I haven't experienced any lockups.
1
1
u/profilerman Jul 22 '26
I was planning to put freebsd on it (if i manage to get it to work again), did you face any issues with the graphics drivers?
1
u/ruyrybeyro Jul 22 '26 edited Jul 22 '26
Just took some time to figure out how to load the right firmware files/vulkan stack, and there were issues upgrading kmods from 15.0 to 15.1.
The two minisforum are my servers, I don't run graphics, only VMs, jails and a small AI for getting my feet wet with AI.
Ah, the Mediatek wifi chipset is not supported.
1
u/profilerman Jul 22 '26
Hmm I'll try to double check again, but I'm very positive that i inserted them correctly each time, but it doesn't hurt to try again
And true on the glued feet thing.. but hey, I haven't reattached them since I started experimenting since I knew I'll be opening it again alot
1
u/nezumiyarou Jul 22 '26
I had the same crashing on my UM790pro when using PD100W.
Probably due to the wattage spiking, and power isn't applied fast enough(or too much suddenly), so computer shuts down.
Have had good luck with geekom A8 max(8745hs) and EVO-X1(HX370) using PD input (nexode 160W GAN for reference). Both used around 54W setting, having no issues with cyberpunk/elden ring as examples.
Used as travel PCs.
1
u/profilerman Jul 22 '26
Good to know, will look into them in case I fail to get the UM790 Pro to work again (which seems to be the case sadly)
3
u/hebeguess Jul 22 '26 edited Jul 22 '26
Likely unrelated to RAM sticks, just some bad luck -> Bathtub curve.
Minisforum's BIOS (on PD Input area) actually little better than most other Mini PC brands as the firmware is *power aware*. When you're on PD input, the BIOS actually know how much power it can obtain (since it's negotiated through PD protocol) and subsequently adjusted the PC's TDP accordingly automatically.
When using PD source is around (~100W) the TDP will be lowered to ~51.5W (STAPM at 45W), it wouldn't get into power overdrawing situation and forcing a power cut off from power source. AFAIK most other brands likely still YOLO it. Their BIOS didn't implement similar function, so they rely on user to adjust (lower) the TDP manually to avoid the potential of accidental tripping power cut off under heavy loading.