GTX 1080 Founders Edition Died - 12V to Ground Short

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Hey all, I'd appreciate some help troubleshooting this dead card - if we save it great, if not it is dead anyway...

My GTX 1080 FE died suddenly while gaming, I was overclocked and temps were reasonable ~mid 70C. The whole PC shut down, no lights on the motherboard etc.

TLDR: Trouble shot the system , it's 100% the graphics card, something has failed on it causing the 12V pins to short to the ground pins kicking the PSU protection off to save the system. My best SWAG guess is a mosfet, IC, or transistor is shorting?



I've seen others with GTX 1080 failures due to the tantalum capacitors but the failure methods seem different, but this poersons' issue sounds the most similar: https://www.reddit.com/r/overclocking/comments/cwjdte/gtx_1080_pcb_repairing/

This page has tons of good photos if mine below aren't good enough: https://xdevs.com/guide/pascal_oc/



I've stripped the card down, there is no signs of scorching, no smells of magic smoke, nadda that I can see.

I did a lot of research on graphics cards, their phase design, "stabbing" guides, and stalking RazorWind's different repair threads and videos, but I am certainly still learning a lot and have a lot to learn! I'm not 100% sure about all of the values I've found, and I'm sure I've made some obvious mistakes, so I'd appreciate any guidance on things to try (other than microwaving it :p), otherwise I may start with desoldering components to see when the short disappears (something I've seen Bob Kalpon and other youtubers do)...? I've also seen the Louis Rossman (IIRC) method of dousing the circuit board with alcohol to find hot spots (using an adjustable PSU) since I don't have an IR camera and want to avoid destructive testing, but for now I will poke around with my multimeter.

Card:
top.jpgbottom2.jpg

Power Phases:
phases.jpgphases 2.jpg





Probing Results (Resistance to Ground unless otherwise stated):
Using a milwaukee 2216-20 multimeter, with autosense resistance, it'll round down to 0.0Ω when there is very little resistance FYI.

For this on the mosfets I get these results, assuming the arrow is pointing at pin 1, and pin 4 should be the gate, and 5-8 are drains, I sussed this out since the datasheet doesn't specify for me https://pdf1.alldatasheet.com/datasheet-pdf/view/938419/MGCHIP/MDV3605.html

ina3221.jpg
q36
pin 4 3 2 1
~6M each
____________
pin 8 7 6 5
~4.2k each


q37
pin 4 3 2 1
0.7M, (10k going up?) ,13M , 13M - Need to clean this side up after likely butchering it with probe between pins 2&1 - measures could be off. I'll get my loupe out and see if it's gunk or a leg/solder later.
____________
pin 8 7 6 5
~6M each


q38
pin 4 3 2 1
0.4 0.4 0.4 118k
____________
pin 8 7 6 5
~6M each


The stripe on smd solid capacitors is the positive end, and on the electrolytes it's the negative, I added those measurements anyway. There was a lot of flux and some residue from the thermal pads so I had to dig in with the meter in some places.

From what I've researched, core resistance SHOULD be low, and the memory SHOULD be higher, I didn't find exact numbers for GTX 1080s though. I don't know about these measurements going up into the MΩ on C235,239,276,1176 either? I don't see any obvious shorts from these measurements..:

phases labeled 2eb.jpg


Older probe measures, with the mosfet pin measurements (the above picture supercedes any resistance measurements on the chokes and capacitors), there was flux or residue adding resistance to the ground measurements...
older probing w mosfets.jpg

Thanks for any and all suggestions!
 

RazorWind

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How confident are you in that 0.1 ohms to ground measurement on the 12V input connector? Is it super repeatable?

Edit: This was a great first post, by the way. I wish everyone who asked for help provided that much information.

Edit2: Where are you located, and do you have access to a hot air rework station and/or PCB preheater?
 
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pendragon1

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Edit: This was a great first post, by the way. I wish everyone who asked for help provided that much information.
its almost like hes seen some of your posts/help...
between this post and the other thread, you were first to come to mind. hope you dont mind.
edited speeling
 
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pendragon1

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I had another look at the OP's post this morning, and I think I have this figured out. We've now seen a bunch of failures like this here at [H] in my threads and in those posted by others. Can anyone who has been following along spot what's wrong here?
its missing a power phase at the bottom?! :)
 

Armenius

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I had another look at the OP's post this morning, and I think I have this figured out. We've now seen a bunch of failures like this here at [H] in my threads and in those posted by others. Can anyone who has been following along spot what's wrong here?
The power sense resistor for the 12V on the top-right looks a little "bubbly." Also looks like there is a scorch mark on the PCB to the right of the caps near the bottom mounting hole.
its missing a power phase at the bottom?! :)
The empty pads on the power phase at the bottom is normal for the 1080 FE.
 
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How confident are you in that 0.1 ohms to ground measurement on the 12V input connector? Is it super repeatable?

Edit: This was a great first post, by the way. I wish everyone who asked for help provided that much information.

Edit2: Where are you located, and do you have access to a hot air rework station and/or PCB preheater?
Thank you! I try to be as thorough as possible.

The 12V to ground is very repeatable, I took the measurements thrice, and I did every pin each time. I would stick one probe into pin 1 and test 2-8, then pin 2, test 1 and 3-8, and so on. Any combo of ground and 12V gets me 0.1-0.4Ω every single time.

I'm in Oregon. I've worked with through-hole soldering a bit and done some basic smd repairs, but usually only things with 2-4 pads like capacitors, not ICs with many... No I don't have hot air nor a PCB heater, in the past I've ghetto rigged up a combo that worked but is finicky - a heat gun paired with an IR gun: warm everything up with quick passes and taking heat samples, and using a small butane pencil torch with this grid thing so only hot air comes out. It's a pain in the ass and I usually enlist a helper but I'm willing to get a rework station and a pcb heater, I've heard good things about Hakko but I'm open to any recommendations! Preferably in the hobbyist price range, but I'll invest in whatever I need.

I had another look at the OP's post this morning, and I think I have this figured out. We've now seen a bunch of failures like this here at [H] in my threads and in those posted by others. Can anyone who has been following along spot what's wrong here?
Beats me, that's why I'm here asking! Glad you've spotted something, hopefully it's something I can try to fix. The power supply cut power quickly so I'm hoping the GPU die/memory ICs didn't get bit with 12V...

its missing a power phase at the bottom?! :)
I wish it was that simple. You can see all of the power phases were basically cut in half to save money, plus cutting out a whole phase.
 
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The power sense resistor for the 12V on the top-right looks a little "bubbly." Also looks like there is a scorch mark on the PCB to the right of the caps near the bottom mounting hole.

The empty pads on the power phase at the bottom is normal for the 1080 FE.

If you mean the shunt R53, the factory solder job looks like crap. I can't speak to the quality of the component itself.

I just tested resistance across the 3 shunts that I can see just in case and they all read 0.0Ω which is my meters' lazy way of saying milliohm I guess, which is about right for shunts since they affect the power readings - I've heard overclockers use resistors inline to cheat it for more power, but I haven't done that. Most of my measurements were otherwise from the ground pins of the 8-pin, unless noted (or forgotten to be noted...)

The shunts I checked: from the top of the card that is R52 at the bottom right, R51 at the middle of the right, and R53 at the top right by the 8-pin PCIe.
 
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I had another look at the OP's post this morning, and I think I have this figured out. We've now seen a bunch of failures like this here at [H] in my threads and in those posted by others. Can anyone who has been following along spot what's wrong here?
You don't think the GPU die is shorted/failed somehow... do you? I wasn't even pushing it hard I swear
 

RazorWind

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Beats me, that's why I'm here asking! Glad you've spotted something, hopefully it's something I can try to fix. The power supply cut power quickly so I'm hoping the GPU die/memory ICs didn't get bit with 12V...
If I'm reading your markings right, you have less than 1 ohm between the 12V input and the output of the core VRM to the GPU. What you should have there is a few million ohms, because there's a transistor in the way that switches the 12V on and off really fast to make the ~1.09V the core needs. You also have about 0.4 ohms to ground on all the 12V caps, which it should be noted is approximately the static resistance of the GPU core. What this strongly suggests is that you have the classic high side mosfet failure between the 12V input and the core power rail.

The good news is that there's a pretty good chance that the core is OK. I've never seen this on a 10 series card (because they're only just now becoming "old"), but I've had a number of 980 Tis pass across my workbench with this type of failure, every single one of them worked again after I cleared the short.

So, you have a couple of options for moving forward. One is to supply current at 1.0V into the 12V input and see if any of the components get warm, with concentration on the core power FET packages. Using some isopropanol as an indicator, if you don't have freeze spray or a thermal camera is a good way to improve this test. I would bet you strike out that way, though. All the components you're looking to test are made to handle huge current, and would hardly get warm even with 12V.

The other option is to start removing the FET packages until the short is cleared. Do not attempt this with a torch of any kind. You can use just a hot air station to remove them, but you really need a preheater to install new ones. You'll almost certainly destroy the new FETs when you install them without preheating the board. Those who have read my threads here at [H] may remember Solan's card, where I kept replacing the dead FET package, and it would keep burning out, and I'm pretty sure this was the reason. What I would probably do is remove the FETs from the core VRM one at a time until the short is clear, and then head the board back up, remove the remaining ones as well, and replace all of them with new ones. This includes the one for the memory rail, which I believe is the same part on this board.

If I were in the market for a hot air station, and I thought I'd use it very often, I'd probably try to use that as an excuse to buy the one that Louis Rossmann sells - the name of which escapes me now. Hakko is a good brand too, but pretty expensive. The one you see me use on Youtube is a cheap Aoyue 968A, which includes a pretty nice soldering iron. It's cheap, but effective. I also have the INT866 combination preheater/soldering station, which I like way more than I thought I would. If you were going to fix a lot of cards, you'd want something more powerful, though, like the fancy Hakko one.

If you're ordering a hot air station, make sure the one you get is meant for 110V power. 220V versions exist as well, and won't work in the US unless you have a monster dryer circuit to plug them into.
 
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Thank you so much for your input!

I will see if my 12V meanwell PSU adjusts that low, I don't think it does, so onto fet removal. I agree the torch method would be too reckless for components like that, I feel like a shunt or simpler circuit I could skate by, but mosfets I'd probably rip a trace or burn something out. This is the torch I was talking about, some of the interchangeable bits let you do hot air only (the flame is expelled out of a port on the side), so I'm not a complete lunatic! As far as I recall there is only one setting to have the flame come out for working as a proper torch, the rest are for soldering/hot air: https://www.lowes.com/pd/BernzOmatic-Lead-Free-Soldering-Kit/1000170991 , it is good for when you need to repair something appropriate for a typical iron and don't have power - I can do heat shrink and solder, and this model doesn't need a lighter, but SMD repair is already tough enough so I will get the appropriate tool.

The fet rework will definitely take more finesse than what I was talking about, so I think I will invest in the Aoyue 866. I like that it's an all in one at a decent price, unless you think I would do better else-wise.

Louis Rossman sells the Atten ST-862D for about $250, but I honestly think it'll be overkill for my usage, and I'd still want the preheater. If I have the kit I will use it, but certainly not often enough to expect it to die for several years. Otherwise I'm looking at $400+ for hot air and preheat. I'll also need a new flux paste syringe, I should still have wick, is thin gauge 60-40 solder is fine or is there something better? I will experiment with a dead 9800 GTX+ to get a feel for SMD reworking before trying on the 1080. Anything else I'm missing? I don't have a silicone mat anymore either, probably won't need one with the Aoyue 866 anyway?



I'll probably get 10 mosfets, NTMFD4C85N:

Ebay ~$20, but will it be any more reliable than alibaba in terms of quality?
https://www.ebay.com/itm/5pcs-NTMFD4C85NT1G-NTMFD4C85N-4C85N-QFN8-new-/123248646656?_ul=IL

amazon ~$34, same issue as above. Still coming from China
https://www.amazon.com/4C85N-NTMFD4C85N-NTMFD4C85NT1G-Chipset-Original/dp/B0838TSTTV

Mouser ~48$
https://www.mouser.com/ProductDetail/ON-Semiconductor/NTMFD4C85NT1G?qs=dbuNSGnowt0IPuJj8dK4RA==

Digikey says the have them, I can't seem to add them to my card, not sure if they have a bug or what but looks like I'd have to order 117 of them?
https://www.digikey.com/en/products/detail/on-semiconductor/NTMFD4C85NT1G/11529722

If you think it's all the same I'll snag up some ebay fets, but I'll happily opt for whatever is recommended.




I know card repair is partially experimental, how do you feel about me adding mosfets where NVIDIA held back, restoring it to two per phase? In my mind that would cut the workload/stress in half, hopefully preventing future failures. I checked the pads just in case, they are all connected, so from my understanding there is no reason I couldn't or shouldn't?

I could probably re-add the missing phase too but that TI 53603A and three resistors and capacitor look like a royal PITA being so small, and that's assuming I could reasonably source them and something else isn't missing or changed elsewhere on the PCB so I'll likely can that idea as a fun thought experiment. The card did survive for probably four years of mild gaming with the 5 half-neutered phases.


The memory does use the same mosfets so I'll order a bunch, it looks like I forgot to list the major components, which I'll do so now for posterity's sake:

GPU:
Core: Nvidia Gp104-400-A1 Core
Memory: Micron D9TXS; MT58K256M32JA-100:A 8Gb: x16, x32 GDDR5X SGRAM with rated data rate at 10.0 Gbps

Power Phase:
TI 53603A Dual phase step down controller? Not 100% sure, it's the 8-pin model. Finding the datasheet for the 8-pin is rough.
ON NTMFD4C85N Dual PowerPhase FET , powering the 5 phases to gpu and the 1 to mem
Tantalum ( I believe) Capacitors 330µF and 470µF
R22 and R33 chokes, not sure on the ratings, 12:1 on the r22 maybe?
uP9511P 8/7/6/5/4/3/2/1-Phase Synchronous-Rectified Buck Power Controller
Texas Instruments INA3221 Power Sensor IC for current monitoring, works with the shunts AFAIK

There is probably more but I'll have to double check, I'll edit them in later if I find any major players.
 
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If I'm reading your markings right, you have less than 1 ohm between the 12V input and the output of the core VRM to the GPU. What you should have there is a few million ohms, because there's a transistor in the way that switches the 12V on and off really fast to make the ~1.09V the core needs ... What this strongly suggests is that you have the classic high side mosfet failure between the 12V input and the core power rail.
Just to make sure I understand correctly:
The output of the core VRM to the GPU measurements are the coils/chokes which are supposed to step down to the core voltage?

And the transistors you speak of that flop are the mosfets? Just making sure I'm on the same page over here.

I thought it was quite odd that the memory mosfet read in the MΩ range, but I wasn't sure what number to expect either. As far as I understand now, the mosfets are all working in parallel, so that is why I would have to desolder them all to find the bad culprit?

And going off of that assumption, that is why I'm wondering if I can do an upgrade by adding mosfets to the empty pads since they are all electrically connected anyway (skipping the missing phase)?

Looking at the card again, it looks like it originally was designed to be 6 core phases, and two memory phases with a shared choke? I'm not sure though since there is an odd number of mosfet pads in that location, but 16 in total.
 

Nobu

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Just to make sure I understand correctly:
The output of the core VRM to the GPU measurements are the coils/chokes which are supposed to step down to the core voltage?

And the transistors you speak of that flop are the mosfets? Just making sure I'm on the same page over here.

I thought it was quite odd that the memory mosfet read in the MΩ range, but I wasn't sure what number to expect either. As far as I understand now, the mosfets are all working in parallel, so that is why I would have to desolder them all to find the bad culprit?

And going off of that assumption, that is why I'm wondering if I can do an upgrade by adding mosfets to the empty pads since they are all electrically connected anyway (skipping the missing phase)?

Looking at the card again, it looks like it originally was designed to be 6 core phases, and two memory phases with a shared choke? I'm not sure though since there is an odd number of mosfet pads in that location, but 16 in total.
You'd have to clear the short, and add all the other missing components for that phase. Not sure if the firmware would control that phase either, may have been nuked?
 
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You'd have to clear the short, and add all the other missing components for that phase. Not sure if the firmware would control that phase either
That would be my fear as well, I'm much more interested in doubling up the mosfets on the existing 5 phases than reintroducing the missing 6th.

I've researched down some rabbit holes, sometimes a simple resistor swap is enough to pull a controller to different phase counts, but I don't know really. In the end it wouldn't be worth it especially if I could double up the mosfets on the 5, since mosfets are what likely failed anyway.
 

RazorWind

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Just to make sure I understand correctly:
The output of the core VRM to the GPU measurements are the coils/chokes which are supposed to step down to the core voltage?
Yes. The primary function of the inductors is to smooth the alternating 12V/0V out, producing a sawtooth-ish approximation of 1.09V. The strip of copper between them and the positive side of the capacitors is wired directly to the GPU core.

And the transistors you speak of that flop are the mosfets? Just making sure I'm on the same page over here.
Yes. The flat black components to the right of the chokes are dual N-channel mosfet packages. There are two transistors inside each one - a high side and a low side, sometimes called "upper" and "lower". The high side one switches the 12V input power on and off. The low side one switches the flyback current from the inductor on while the high side is off, so that it powers the GPU as well. On your card, one of the high sides has failed, creating a situation where the 12V is on all the time from one of the phases.

If you look at the datasheet for the 4C85N, you'll see that the drain of the low side and the source of the high side are wired together to one of the exterior terminals, which is called the switch node. The switch node is the terminal that is connected to the chokes, and from there to whatever component you're powering.

I thought it was quite odd that the memory mosfet read in the MΩ range, but I wasn't sure what number to expect either. As far as I understand now, the mosfets are all working in parallel, so that is why I would have to desolder them all to find the bad culprit?
It depends on where exactly you're measuring. If measure from the switch node to ground, you're actually measuring the resistance through the memory circuit, which should be in the tens of ohms on this card (30-40, maybe?). If you measure from the 12V input to ground, you'll get a much higher number. You should get a lower, but still high, number if you measure at either gate pin.
And going off of that assumption, that is why I'm wondering if I can do an upgrade by adding mosfets to the empty pads since they are all electrically connected anyway (skipping the missing phase)?

Looking at the card again, it looks like it originally was designed to be 6 core phases, and two memory phases with a shared choke? I'm not sure though since there is an odd number of mosfet pads in that location, but 16 in total.
I wouldn't attempt to populate the missing pads, but you may be able to use them if you damage the main ones. Concentrate on just getting the board working first, and then worry about modifying it, if you feel so inclined.
 
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Thanks RazorWind, That all makes a lot of sense and answers questions I didn't yet ask even!

Sounds good, and good idea - try to fix it first in case there are any other issues. Any opinion on component sourcing, or just get it however I can?
 

RazorWind

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Thanks RazorWind, That all makes a lot of sense and answers questions I didn't yet ask even!

Sounds good, and good idea - try to fix it first in case there are any other issues. Any opinion on component sourcing, or just get it however I can?
I've heard tell of some folks getting counterfeit parts from ebay, but I've never actually had that happen myself. I say go for it.
 
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I've heard tell of some folks getting counterfeit parts from ebay, but I've never actually had that happen myself. I say go for it.
Order says ~June 17th, it's on the slow boat but that gives me a chance to practice on some old junk cards!

I have one with a bad PCB, you can hear crunching when lightly flexing it, I'm assuming traces. Found that out pulling the heat sink, it's a low end old card anyway, or I have the 9800 gtx+. I can play doctor and pull, retin, and reattach some mosfets on those to get the hang of it.
 

WilyKit

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One of the most entertaining and informative threads on [H] I’m anxiously awaiting the results of the repair.
 
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First of the tools came in! I got a cheap USB microscope to help make sure I don't miss anything! I also got more solder wick, flux, etc but the reflow station won't be in until Monday or later.

Below here are some closer images of the main components needing addressed. I'm not sure if Q37 was smooshed' when I was probing, regardless that is a solder blob by the look of it. I should have used safety pins instead of the probes for testing resistance, oh well it's too late now. It's also blocked in part by that cap, so I'm thinking Kapton tape and tinfoil to isolate it from neighboring components, that might help keep me from blowing other components away? Kapton is good till about 500ºF supposedly, I've had luck with it and tinfoil in the past.

Otherwise I can rig up a very fine soldering tip if the kit I got doesn't have one fine enough, although if I could jab a probe in there I'm sure I could fit a very fine tip (or perhaps I'll wrap some copper wire around the tip for a DIY thinner tip) ... I'll test the Kapton on a sacrificial card first to see how well it protects the little components from getting blown away to sate my curiosity, but I'm liking the thinner tip idea for Q37 because of the close proximities...

Q37 MDV3605 MOSFET https://datasheetspdf.com/pdf/1107906/MagnaChip/MDV3605/1 (I believe):
v3605 pin smoosh.jpg

Core and Mem ON NTMFD4C85N Dual PowerPhase FET (4C85N MOSFET) up close:
4c85n mosfet.jpg4c85n mosfet2.jpg

That's all for now. The new MOSFETs won't be here till mid-June'ish, but I can start pulling them one by one to see if/when the 12V/ground short drops off at least when the hot air kit comes in.
 
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I've got everything but the mosfets and air flow setup, so I whipped out the test victim. I don't want to go in cold on my GTX 1080 so I will be practicing on a 9800 GTX+ that died, I wish it worked for one of my old socket 939 builds but oh well.

Being antsy and wanting to experiment I tried the heat gun "preheat", with the micro torch on hot air. That setup was actually very serviceable, although you would want a helper to be able to pass off the heat gun back and forth as needed to maintain warmth - I used it to get the area evenly warmed, then using the butane torch hot air attachment for the actual desoldering. It only passes hot air, the flame is vented out the sides, and it just gets hot enough to melt the lead-free solder.

I used an old scrap of 3/4 ply underneath, preheating that as well with the heat gun so it would draw less heat from the PCB, and protect the work surface. RazorWind don't worry, I wouldn't dare try this on the GTX 1080! The hot air / preheater combo is coming, I'm just impatient to start practicing and getting a feel for SMD work again.

Sadly my torch ran out of butane right after removing the uP7706AU8 IC, the closest in size and having a similar layout to the mosfets on the GTX 1080, albeit with longer legs.

Do NOT try to do any reflow work with just a heat gun, they blow too much air which will cause the smaller components to float away. I may have tested a section just to see how it would do, it was BAD!

Anyway, pics:

Before
the bigger victim.jpgthe victim.jpg

After pulling the IC, running out of Butane on reassembly, murdering everything with the heatgun:
the IC by itself.jpgoh the humanity.jpg

I cleaned up the pads after the heatgun incident, before I got tired of bothering. You can see C37 halfway falling off still. I did remount the IC ultimately, and get all but one component tacked back on with my soldering iron, but a hot air reflow (or my butane) would do it much better. One of the tiny resistors floated away or stuck to something, oh well.
cleaning up after hg.jpg (Forgot after pic, may add later)
 

RazorWind

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I've got everything but the mosfets and air flow setup, so I whipped out the test victim. I don't want to go in cold on my GTX 1080 so I will be practicing on a 9800 GTX+ that died, I wish it worked for one of my old socket 939 builds but oh well.

Being antsy and wanting to experiment I tried the heat gun "preheat", with the micro torch on hot air. That setup was actually very serviceable, although you would want a helper to be able to pass off the heat gun back and forth as needed to maintain warmth - I used it to get the area evenly warmed, then using the butane torch hot air attachment for the actual desoldering. It only passes hot air, the flame is vented out the sides, and it just gets hot enough to melt the lead-free solder.

I used an old scrap of 3/4 ply underneath, preheating that as well with the heat gun so it would draw less heat from the PCB, and protect the work surface. RazorWind don't worry, I wouldn't dare try this on the GTX 1080! The hot air / preheater combo is coming, I'm just impatient to start practicing and getting a feel for SMD work again.

Sadly my torch ran out of butane right after removing the uP7706AU8 IC, the closest in size and having a similar layout to the mosfets on the GTX 1080, albeit with longer legs.

Do NOT try to do any reflow work with just a heat gun, they blow too much air which will cause the smaller components to float away. I may have tested a section just to see how it would do, it was BAD!

Anyway, pics:

Before
View attachment 358495View attachment 358497

After pulling the IC, running out of Butane on reassembly, murdering everything with the heatgun:
View attachment 358496View attachment 358494

I cleaned up the pads after the heatgun incident, before I got tired of bothering. You can see C37 halfway falling off still. I did remount the IC ultimately, and get all but one component tacked back on with my soldering iron, but a hot air reflow (or my butane) would do it much better. One of the tiny resistors floated away or stuck to something, oh well.
View attachment 358493 (Forgot after pic, may add later)
Didn’t you say you ordered an Aoyue 866? Why not use that? Also, you need flux.
 
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Didn’t you say you ordered an Aoyue 866? Why not use that? Also, you need flux.
I got flux and the Aoyue 866 will be here soon, it's delayed now to May 27th... just a practice run in futility, that card has a broken PCB so it's just good for practice unless anyone needs a component. There's a couple other ICs that are mosfet-like that I am saving for the Aoyue practice runs.

The flux is Chip Quik NC191, I wanted to make sure that stuff worked OK, since I almost opted for the MG Chemicals flux at twice the price. My 60/40 solder worked fine to retin the components but I'm thinking I'll need to get fluxless solder, not this rosin core?

Thanks again for all the help
 

KD5ZXG

Gawd
Joined
Mar 24, 2017
Messages
669
If you mean the shunt R53, the factory solder job looks like crap. I can't speak to the quality of the component itself.

I just tested resistance across the 3 shunts that I can see just in case and they all read 0.0Ω which is my meters' lazy way of saying milliohm I guess, which is about right for shunts since they affect the power readings - I've heard overclockers use resistors inline to cheat it for more power, but I haven't done that. Most of my measurements were otherwise from the ground pins of the 8-pin, unless noted (or forgotten to be noted...)

The shunts I checked: from the top of the card that is R52 at the bottom right, R51 at the middle of the right, and R53 at the top right by the 8-pin PCIe.
Sounds like you need a 4wire ohmmeter, or fake it with two meters.

One on Ohms only to send the test current. Don't use to measure. Always slightly off due to its own cable resistance.

The other on Volts to measure the drop across devices in question. Without the distraction of send current in the cables.

Might also want to solder send and sense together near the tips, so you are only handling one pair of probes, not four.

Some call this a Kelvin connection, not entirely sure why.

If 1st meter on autoscaled ohms don't present a constant current, could also try diode check for the send current.

Receive volts may not tell you actual ohms, but it also won't be measuring a zero or jumping around.

Then go hunting for the shortest short. Should be able to tell which half of the board anyway.

 
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Joined
Mar 26, 2020
Messages
49
The hot air reflow station arrived today, so I'll do some practice runs properly this time around on the test victim 9800 GTX+ first. If that goes well, I'll pull mosfets down and see if the short disappears.

KD5ZXG thanks for that information! I've heard about 4-wire measurements but hadn't considered it. I'll keep learning about that.
 
Joined
Mar 26, 2020
Messages
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Mosfets show as having arrived. We'll see how far I get this weekend. My plan is to begin pulling the old mosfets with my new hot air setup, after a little more practice on the sacrificial 9800 gtx+
 
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