Legion 5i 5-17IMH05H shunt mod assistance

hi, i have tried 115w vbios from other laptops and the gpu works with them but it will only work in optimus/hybrid mode and losing discrete mode is a non-starter for me.

i was hoping someone could help me figure out if a shunt mod should work and if so possibly help me figure out which shunt resistors i should try. i'll include some images from the front/back side of the motherboard, i believe the 2 "R005" resistors on the back side of the gpu area are the correct ones but confirmation would be great.

Front MB:



Backside MB:

 

Who gave you the idea to shunt mod your laptop?

 

The Legion5i 17 is not an enthusiast type of gear that is friendly with modifications. I wonder why TS tries on that stunt.

 

that would be me, i figured since the 115w vbios works on it and pulls 115w without causing instability or even coming close to thermal limits that a shunt mod would behave the same but without breaking features that i need/want like running in discrete mode or being able to use external ports. is this faulty logic?

im familiar with soldering but i wanted to ask someone more familiar with shunt mods what my limit should be or if there is any very clear reason why i shouldnt do it on this particular laptop.

sorry, i dont know you mean? i know it's not a $3000 laptop but it has plenty of thermal headroom as well as power to spare but from what i understand, those are not the only deciding factors so im asking here

 

Then I was right to come to this thread. I was the first to do shunt mods on laptops.

But if I'm not mistaken from the pcb, the gpu vrm only has 3 phases. Can you take a picture of the Vrms? They are located below the gpu.

 

unless im mistaken i think the vrms are on the back of this mb, the last image above?

 

No, it's in the front.

I'm think it's a 3 phase from a glance at the pcb but I can't confirm until i see the front

 

yeah your right, right now lenovo has the laptop for repair so im trying to find a full front board image. i took about 30 photos of the board and just now realized not 1 of them is a full frontal image

best i have at the moment, im looking for a better image. am i right to assume that an rtx 2060 would have less vrms than say a 2080smq like yours?

 

i found a full image of the front, looks like 3 large + 2 small yes?

 

Yeah unfortunately you can't go above 120w with that vrm. 3 phases for 115w is already really perilous considering it doesn't even have a heatpipe over the vrms.

 

im only looking for 115w, or 110w if you feel thats a safer bet. i did do a little stress testing when i had the 115w vbios flashed and it sat at a steady 115w.

im a bit limited for images of when i was using it but this is during one of many benchmarks of Horizon: Zero Dawn and it ran great. that game is extremely taxing and often unstable but i had no problems


right now, the 80w (original vbios) seems like such a waste of potential. and those temps were from before i switched over to LM

 

So you want to get around 115w but with the stock vbios? I assume that is 80w?

The closest you can get is 100w by swapping our the R005 shunt resistors with R004 shunt resistors.

If it's 90w then you can get to 112.5w

 

im not opposed to using a modded vbios but from what i understand this is not possible on these gpus? and using a vbios from a 115w laptop (i've tried many) the result is having to use optimus mode which i dislike quite a bit and also lose external port functionality.

the stock vbios are 80w but usually run at a constant 85-86w under load/gaming, would that mean i would end up with around 106.25w ?

 

Yeah somewhere there.

 

thats still about 20w more than i have now, and i think the heatsink does cover them (working from memory and pictures online). out of curiosity, what would be the next step up and with what resistors?

and thanks btw for answering my questions, i appreciate it

 

There isn't a next step up. The Vrms can't handle more than 120w.

Just a metal plate over the Vrms isn't enough btw. You need heatpipes.

 

sounds good, i can be happy with the extra 20w. i was looking on digikey.com for the R004 resistors but they list a ton of them in different wattage, how could i figure out which one i would need?

 

Wattage rating doesn't matter, just get one that has a similar size to the ones on your motherboard.

 

i meant to ask you, is there a particular reason why a shunt be soldered this way as opposed to soldering them flat to the board as originally designed?

 

You shouldn't follow this. Just desolder the R005 resistors and solder R004 resistors on there.

 

thanks again for the info, if lenovo doesnt tell me to fsck off and actually repairs the laptop then i'll be doing this once it comes back to me.

if i do the shunt mod is that gonna effect the usage/power readings? for example if i change the shunt resistors, even though it's drawing more power will it no longer report as 100% usage?