Help to identify some ultra tiny caps

Thread Starter

adelage

Joined Aug 22, 2014
38
Hi all
I am a newbie trying to learn some electronics/soldering by myself, and I bumped into a wall that maybe someone a bit more expert than me can help me to climb:
for some reasons that would be too long to explain, I need to solder some caps on the following pcb
BA23A1A3-55F8-4B0F-B63D-2D2961F2D3D9.jpeg

as you can see on the area marked in blue there are several spots where there should be the same caps that are in the yellow area, and I want to solder them, now I removed one of the caps on the right, and it measured about 0.26uf, the size is about 1mm long, maybe a bit less, what do I have to look for to find some of these caps? I mean, I don’t understand which are the standard values for this thing, I tried to recover some caps which have the exact same size from other boards, but they all measure between 90 and 120nf, maybe I can use them instead? My understanding is that those caps are working as filters along some pci-express data lines, so maybe the exact value is not so important?
Thanks
 
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dl324

Joined Mar 30, 2015
11,872
I removed one of the caps on the right, and it measured about 0.26uf, the size is about 1mm long, maybe a bit less, what do I have to look for to find some of these caps?
Physical dimensions of ceramic surface mount caps are not indicative of their value and caps in that form factor have no labels. Unless they're bypass caps, you need a schematic to determine appropriate values. 0.26uF isn't a typical bypass cap value.
 

ronsimpson

Joined Oct 7, 2019
1,017
1597535549941.png
1mm length? That gives me the idea it is a 0402 (1005 Metric) size.
The next larger size is 0603 (1608 Metric) 1.6mm x 0.8mm.

The capacitor might be 0.22uF.
Do you know what voltage is applies to the caps? Ratings are 6.3V, 10V, 16V

The open spots might not be for capacitors. Resistors and inductors come in the same size packages.
 

Thread Starter

adelage

Joined Aug 22, 2014
38
I am 99% sure that the open spots are meant to have some caps soldered there, and the value should be the same of the caps that are soldered on the yellow area, because every graphic card has pretty much the same layout, the board I am working on is missing them to limit the pcie bandwidth to x4 (instead of x16)..now, I did a bit of research and I found that the smallest one are 0201, and I think that’s the right package, why do you think that the rated value should be 220nf? Is 260nf not a common value?
 

MrChips

Joined Oct 2, 2009
22,089
The value of the capacitance was selected by the designer of the circuit. You would have to ask the designer what value to use.
 

jpanhalt

Joined Jan 18, 2008
10,501
I am 99% sure that the open spots are meant to have some caps soldered there, and the value should be the same of the caps that are soldered on the yellow area, because every graphic card has pretty much the same layout, the board I am working on is missing them to limit the pcie bandwidth to x4 (instead of x16)..now, I did a bit of research and I found that the smallest one are 0201, and I think that’s the right package, why do you think that the rated value should be 220nf? Is 260nf not a common value?
There are lots of open component spaces on that board. Do you think all those parts just fell off? Most likely, there are different versions of that board. Now, let's say you can replace all of the caps with the correct/intended sizes. What will happen:
1) Nothing. Thing will work as before;
2) Thing will be moded up or down to another version.
3) Thing will not work and another currently working part might be damaged.
4) ~ ????
Then, what about all the other "missing" parts?

Almost certainly, any modern board like that will have an MCU. Along with changing the components on the board, you would need to reprogram the MCU, and just maybe, remove some of the parts that are there.. What is the probability you have that code? Can you identify the missing transistors? (3-pin devices)

While you may be 99% sure those components are needed, if the board currently works, I am much less the 1% confident they are needed or intended. Fixing things that aren't broke based on guesses is not a good plan.
 

Thread Starter

adelage

Joined Aug 22, 2014
38
There are lots of open component spaces on that board. Do you think all those parts just fell off? Most likely, there are different versions of that board. Now, let's say you can replace all of the caps with the correct/intended sizes. What will happen:
1) Nothing. Thing will work as before;
2) Thing will be moded up or down to another version.
3) Thing will not work and another currently working part might be damaged.
4) ~ ????
Then, what about all the other "missing" parts?

Almost certainly, any modern board like that will have an MCU. Along with changing the components on the board, you would need to reprogram the MCU, and just maybe, remove some of the parts that are there.. What is the probability you have that code? Can you identify the missing transistors? (3-pin devices)

While you may be 99% sure those components are needed, if the board currently works, I am much less the 1% confident they are needed or intended. Fixing things that aren't broke based on guesses is not a good plan.
I didn’t want to go too much into detail because what I needed were some suggestions about how to identify a component..please don’t misunderstand, I appreciate your point and suggestions, but there are a few things I haven’t mentioned:
1 - this board is a mining only Nvidia gpu (p102-100)
2 - this board design was made in a rush during the mining madness, and this particular manufacturer (zotac) used the same pcb they used for a standard gpu (gtx 1080)
3 - The only visible difference comparing the two pcbs (mining and standard) are those caps, which are missing in the mining version, because Nvidia handicapped these cards on purpose, limiting the pcie bandwidth
4 - the caps missing are interrupting the data lines of pcie 8x/16x, so that the motherboard only gets a 4x connection, and there’s no reason to believe that the value of the caps should be different since they all do the same job

now, of course there might be some things that I am missing, like this MCU programming you are talking about (btw, what is it??), and, most importantly, the fact that the limit has been enforced on a vbios level as well, but since I got the board for cheap and I am just trying to learn something, I will have a go anyway!
p.s.: tnks to everyone for your replies!
 
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