Motherboard ground connector not picking on mulitimeter

[Jaegar]

I have an MSI B450m bazooka plus motherboard, had a blackout and didn't power on pc till next day, I use a surge protector of course. Next day when trying to power it up, the pc wasn't powering up at all, I tried shorting the power on pins on the motherboard and still nothing, I also drained the cmos and nothing. I removed the psu tried it and it works. No any signs of burn on the motherboard, I tried testing with multimeter and one of the ground pin connector(ground 17 on the picture) on the board wasn't connecting with the ground (vga plate), while the rest were connecting using the multimeter. Is this noemal or is something wrong with this?

 

[Bill_Bright]

I don't know what you mean by VGA Plate.

I removed the psu tried it and it works.

How did you try it if it was removed?

Note Pin 17 is the return for Pin 16. These are the two pins you can use to test if a PSU is able to turn on, by shorting the two pins. This is commonly called the "paperclip test", as seen here. This test is NOT conclusive by any means. It only tells you if the PSU is able to turn on or not. It does not test to ensure each of the voltages are present or within tolerances. Nor does it test for ripple and other anomalies. If the PSU does not turn on with this test, it does tell you the PSU is bad.

A better way to test a PSU is with a tester as shown in that same link. It still is not conclusive because it only presents a small 10Ω "dummy load" instead of a variety of realistic loads. But it does tell you if all the required voltages are present and (at least with that load) their actual voltages. I keep one of those testers in my tool bag for house calls.

The only way to conclusively test a PSU is with an oscilloscope or dedicated power supply analyzer, under a variety of loads. Since most users don't have access to these expensive pieces of test equipment, or have the necessary training to use them, the next best way to conclusively test a PSU is to swap in a known good one and see if your problems persist, or go away.

I recommend you beg, borrow or steal a known good PSU from another computer, swap it in and see if your computer boots okay.

 

[Redwoodz]

I believe you should not have continuity from + voltage to ground. That would tell you have a short in the motherboard.

 

[ty_ger]

I believe you should not have continuity from + voltage to ground. That would tell you have a short in the motherboard.

I think you will. There is a lot of parallel circuitry that will add up to low resistance.




I wonder how you will know that the PSU is working properly when disconnected. Please describe your testing process.

 

[Bill_Bright]

I think you will.

Redwoodz is right. With power removed, there should be no continuity from +V to ground as that would be a short. It should measure as an open.

There is a lot of parallel circuitry that will add up to low resistance.

Ummm, that is not how it works. In fact, parallel circuits effectively increase the size of the conductor, essentially creates a bigger wire (like 2 stands instead of 1). And a larger conductor results in reduced resistance.

I wonder how you will know that the PSU is working properly when disconnected. Please describe your testing process.

Yeah, this I wondered above too. We need the OP to return with more information.

 

[qxp]

It would be surprising if the ground pin failed. It's possible that the motherboard has some sort of isolation (like an optoisolator) and pin 17 is not connected to ground. If pin 17 were connected to ground you should see a short between it and other ground pins on the same connector.

 

[ty_ger]

Redwoodz is right. With power removed, there should be no continuity from +V to ground as that would be a short. It should measure as an open.


Ummm, that is not how it works. In fact, parallel circuits effectively increase the size of the conductor, essentially creates a bigger wire (like 2 stands instead of 1). And a larger conductor results in reduced resistance.

I think you guys both misunderstood the OP's context. The OP is measuring the power and ground pins on the motherboard. Between power and ground, the resistance will measure very low. That is normal. You can't test for a motherboard short in this way.

Try it yourself.

It would be surprising if the ground pin failed. It's possible that the motherboard has some sort of isolation (like an optoisolator) and pin 17 is not connected to ground. If pin 17 were connected to ground you should see a short between it and other ground pins on the same connector.

Pin 17 won't measure continuity to other grounds. Or will measure high resistance. It is a switched input/output (depending on your point of view).



I think the OP's measurements so far are irrelevant or not conclusive.

 

[Bill_Bright]

I think you guys both misunderstood the OP's context.

IMO, the OP was not very clear. Or at least, I don't get a clear picture from his description. He said,

and one of the ground pin connector(ground 17 on the picture) on the board wasn't connecting with the ground (vga plate),

I don't know what a VGA plate is for one. That's why I asked for more information.

HOWEVER, after your comment and reading it again, he does say, "on the board". That said, if he meant Pin 16 (PS-On) then I believe you would be right. There should be other components in that circuit that would have resistance. But I note he said Pin 17 was not indicating a ground. That should. Unfortunately, I don't have a spare motherboard here to test.

In any case, IMO, that is not a proper test anyway. And I agree with qxp - unless there was physical damage to the motherboard, like broken pins or a screwdriver cutting through circuit traces, it is highly unlikely any connections on that 24-pin motherboard connector failed.

Bottom line: we need more information.

 

[qxp]

I think you guys both misunderstood the OP's context. The OP is measuring the power and ground pins on the motherboard. Between power and ground, the resistance will measure very low. That is normal. You can't test for a motherboard short in this way.


Pin 17 won't measure continuity to other grounds. Or will measure high resistance. It is a switched input/output (depending on your point of view).

My understanding of the OP post is that he/she tried to verify ground power connector connection by measuring continuity to a ground plane of the VGA card because it was easy to access. What OP found that all the ground pins of the motherboard connector except one - pin 17 - show continuity to VGA ground plane, as you would expect as PCI/PCIe connector has ground pins. The OP question is why is pin 17 not showing continuity even though it is marked ground on the spec. One possible reason is that the connection is poor, but it is more likely the motherboard was designed with pin 16 and pin 17 having a separate circuit that is activated with an optoisolator, or something similar that separates grounds.

The reason they did it is that specification calls for power supply pins 16/17 being safe to prevent high voltage reaching the case and/or power button in case of a fault. An optoisolator adds a bit to cost of the motherboard, but is a simple means to make the motherboard safe as well.

 

[Bill_Bright]

You are making a lot of assumptions I would not. The OP said VGA "plate". You apparently assume he means "ground plane". There is neither on a motherboard that I am aware of - except, maybe, some motherboards have a "backplate" for the CPU that may act as a ground plane. To me, the closest thing to a ground plane (or plate) for a graphics card would be the back of the computer case where the card's mounting bracket mates with the case's back panel. That whole back panel could easily be considered a ground plate.

I doubt they use optoisolators. They are relatively expensive, relatively big, and typically used in higher voltage, higher current circuits. As you suggested, it is more likely they use "something similar".

 

[qxp]

You are making a lot of assumptions I would not. The OP said VGA "plate". You apparently assume he means "ground plane". There is neither on a motherboard that I am aware of - except, maybe, some motherboards have a "backplate" for the CPU that may act as a ground plane. To me, the closest thing to a ground plane (or plate) for a graphics card would be the back of the computer case where the card's mounting bracket mates with the case's back panel. That whole back panel could easily be considered a ground plate.

A "ground plane" is a large copper filled area on PCB electrically connected (or considered) as ground.

Ground plane - Wikipedia

en.wikipedia.org

I doubt they use optoisolators. They are relatively expensive, relatively big, and typically used in higher voltage, higher current circuits. As you suggested, it is more likely they use "something similar".

They are commonly used in power supplies, and motherboards can be more expensive. So not impossible. The manufacturers get good pricing, they are not buying single units.

Looking at the image below next to the power connector you can see a largish chip with 8-pins. I don't think it is a switcher, because the coils above are connected to two smaller chips to their right. I suspect this is an optocoupler, or an integrated device that has an optocoupler.

https://image.made-in-china.com/2f0j00vMbhCHLEfwuK/Standard-ATX-Specification-Q470-Chipset-Industrial-Motherboard-Computer-Motherboard.webp

 

[Bill_Bright]

I know what a ground plane is. You can follow the link in my sig to see I might know a little about that - especially with my background with radio systems.

My concern is, that is NOT what the OP said. He said VGA plate. I am not assuming he meant the same plate. And if you note your own link, when it comes to PCBs, a ground plane is often located on the "bottom" of the board, not top where the card's socket it.

I also know what optoisolator is and where they are commonly used - and they are NOT commonly used in motherboards because as I noted, they are typically used with higher voltages and currents.

Even if the OP's board has one, the device used is off topic.

Looking at the image below next to the power connector you can see a largish chip with 8-pins.

I really don't understand you. That is not meant to criticize - just stating an observation. Why are you showing us a motherboard the OP does not even have? That makes no sense whatsoever.

As I noted above, we need more information so I see no reason to continue this discussion until the OP comes back with more information.

 

[qxp]

I know what a ground plane is. You can follow the link in my sig to see I might know a little about that - especially with my background with radio systems.

My concern is, that is NOT what the OP said. He said VGA plate. I am not assuming he meant the same plate. And if you note your own link, when it comes to PCBs, a ground plane is often located on the "bottom" of the board, not top where the card's socket it.

My understanding is that the OP had one multimeter connection on an obviously grounded part of VGA card that was plugged into PCI/PCIe slot. Alternatively, it could be he/she meant the shield around the DVI connector. For a card plugged into PCI/PCIe slot the bottom of the board would be easily accessible.

I also know what optoisolator is and where they are commonly used - and they are NOT commonly used in motherboards because as I noted, they are typically used with higher voltages and currents.

There are many different kinds of optoisolators/optocouplers. I had something like this in mind:

https://www.mouser.com/ProductDetail/Lite-On/CNY17F-1?qs=gnaPJ2cis72bTkQCnAIJ0w%3D%3D

It costs $0.14 in single quantities and works like a transistor with optically activated gate. You connect the transistor between pins 16 and 17 and you have isolation.

Even if the OP's board has one, the device used is off topic.

Its on topic, because an optoisolated connection would not necessarily connect pin 17 to ground, which would explain OP observations.

I really don't understand you. That is not meant to criticize - just stating an observation. Why are you showing us a motherboard the OP does not even have? That makes no sense whatsoever.

There is a question - do motherboards have optocouplers ? The question can be solved by finding a motherboard that does. I did a quick look online and found one that appears to have an optocoupler - though, unfortunately, the image resolution is not good enough to read off the part number.

The OP motherboard image is also hard to read (link below). It does have a similar 8-pin device but it is smaller and closer to RAM modules and so I am not sure whether it is not a voltage regulator instead.

https://images.anandtech.com/doci/13091/MSI%20B450M%20Bazooka%20and%20B450M%20Bazooka%20Plus%20Motherboards.jpg

 

[Bill_Bright]

There is a question - do motherboards have optocouplers ?

No there isn't. Nobody asked that question. Certainly the OP didn't.

This is you, once again, trying to run another thread off topic again.

We need more information from the OP. Until then, this thread is on hold.

 

[qxp]

No there isn't. Nobody asked that question. Certainly the OP didn't.

This is you, once again, trying to run another thread off topic again.

The original question is why is pin 17 not connected to ground ? One possibility is that the motherboard uses an optocoupler and it is not connected to ground by designed. You claimed that motherboards don't have optocouplers. So I went to check and found a possible example. Thus it is likely that OP motherboard pin 17 is fine. Entirely on topic.

We need more information from the OP. Until then, this thread is on hold.

Or one can use the information provided to reason out the answer.

 

[Bill_Bright]

You claimed that motherboards don't have optocouplers.

No I didn't So you attempting to justify your actions by making falsehoods only makes you look less credible.

So PLEASE, stop trying to impress others by driving this thread off topic with untruths and instead, lets wait until we get more information from the OP about what his or her actual problem is. Then we can give some sound advice based on actual information instead of your guesses and assumptions.

 

[ShrimpBrime]

No I didn't So you attempting to justify your actions by making falsehoods only makes you look less credible.

So PLEASE, stop trying to impress others by driving this thread off topic with untruths and instead, lets wait until we get more information from the OP about what his or her actual problem is. Then we can give some sound advice based on actual information instead of your guesses and assumptions.

Yes, like make and model of everything in the system including the surge protector.

But from the symptoms, the board at least sounds broken. I wager a lightning strike against unprotected home circuits can take out pretty much all and any electronics even on a surge protector.

Like ExiledAirman would say, "bring it to a shop for diagnostics if you don't have the extra hardware and knowledge to do it yourself." I stand by this statement for this one.

 

[qxp]

You are making a lot of assumptions I would not. The OP said VGA "plate". You apparently assume he means "ground plane". There is neither on a motherboard that I am aware of - except, maybe, some motherboards have a "backplate" for the CPU that may act as a ground plane. To me, the closest thing to a ground plane (or plate) for a graphics card would be the back of the computer case where the card's mounting bracket mates with the case's back panel. That whole back panel could easily be considered a ground plate.

I doubt they use optoisolators. They are relatively expensive, relatively big, and typically used in higher voltage, higher current circuits. As you suggested, it is more likely they use "something similar".

This is your message saying you doubt motherboards have optocouplers.

The original question is why is pin 17 not connected to ground ? One possibility is that the motherboard uses an optocoupler and it is not connected to ground by designed. You claimed that motherboards don't have optocouplers. So I went to check and found a possible example. Thus it is likely that OP motherboard pin 17 is fine. Entirely on topic.

No I didn't So you attempting to justify your actions by making falsehoods only makes you look less credible.

And now you say you did not.

So PLEASE, stop trying to impress others by driving this thread off topic with untruths and instead, lets wait until we get more information from the OP about what his or her actual problem is. Then we can give some sound advice based on actual information instead of your guesses and assumptions.

How about you stay on topic, and use a more professional language ?

The OP has asked a very straightforward question - should pin 17 be connected to main ground on the motherboard or not. They did not ask for any advice on what to plug in. Just yes or no answer or some information to figure it out. Does your motherboard have pin 17 connected to main ground ? My motherboards don't have this connector, as I got Dell's 5820s and 7920s, so I can't test myself.

 

[Jaegar]

I don't know what you mean by VGA Plate.


How did you try it if it was removed?

Note Pin 17 is the return for Pin 16. These are the two pins you can use to test if a PSU is able to turn on, by shorting the two pins. This is commonly called the "paperclip test", as seen here. This test is NOT conclusive by any means. It only tells you if the PSU is able to turn on or not. It does not test to ensure each of the voltages are present or within tolerances. Nor does it test for ripple and other anomalies. If the PSU does not turn on with this test, it does tell you the PSU is bad.

A better way to test a PSU is with a tester as shown in that same link. It still is not conclusive because it only presents a small 10Ω "dummy load" instead of a variety of realistic loads. But it does tell you if all the required voltages are present and (at least with that load) their actual voltages. I keep one of those testers in my tool bag for house calls.

The only way to conclusively test a PSU is with an oscilloscope or dedicated power supply analyzer, under a variety of loads. Since most users don't have access to these expensive pieces of test equipment, or have the necessary training to use them, the next best way to conclusively test a PSU is to swap in a known good one and see if your problems persist, or go away.

I recommend you beg, borrow or steal a known good PSU from another computer, swap it in and see if your computer boots okay.

Indeed I used the paper clip method to test the psu, don't have any other testers. Currently don't have access to another psu I can test, but will try to secure one

 

[Bill_Bright]

@Jaegar - my apologies for my part in these distractions. I assure you, we are all trying to help. But first, we need to understand the problem better. Note power "outages" may corrupt data on drives, but do not harm computers. However, when power is "restored", it often is not restored "cleanly". There often are extreme fluctuations as, all at once, 100s or 1000s of lights, air conditioners, furnaces, water heaters, TVs, refrigerators and other appliances across the entire grid section attempt to power up at the same time. It is the surges and spikes during these fluctuations before the grid stabilizes that can damage electronics.

We (mere humans) often "see" these fluctuations as lights "flickering". But it is important to note that even greater and more destructive surges and spikes can last just a few nanoseconds, much much faster than our brains can perceive.

Understand too that surge and spike protectors are little more than fancy and expensive extension cords. They certainly are better than nothing but note they do nothing for low voltage events like dips (opposite of spikes), sags (opposite of surges) or brownouts (long duration sags). And for excessive surges and spikes, they simply cut power (“IF” working properly), crashing your computer - never good.

AND - surge and spike protectors wear out! This is why it is recommended surge and spike protectors be replaced every 2 years. And if damaged by an extreme high-voltage event, they may still provide power to the connected devices, but may provide little to no protection at all - even if less than 2 years old. So I always recommend computers be supported by a good UPS with AVR instead. The AVR (automatic voltage regulation) adjust for both high and low anomalies. But that's for a different discussion.

Now nothing can protect us from a direct lightning strike from Mother Nature. But short of unplugging from the wall, a good UPS with AVR is the next best thing.

Again, we need more information about your hardware. Filling out your TPU System Specs would help with that.

Did you try booting connected directly to the wall - that is, without the surge and spike protector? If still no good, since EVERYTHING inside the computer case depends on good, clean, stable power, you need to ensure you are providing it. As suggested above, you need to try another, known good PSU and see what happens. Hopefully, that will resolve your problems.

***

@qxp - Okay, I'll give you the benefit of the doubt and assume you are still learning English. When someone says they "doubt" something exists, that is not the same thing as saying "they don't" exist. For example, I "doubt" bigfoot exists. I find it highly unlikely there would be zero DNA, scat, or skeletal evidence discovered by now if bigfoot was real. If something is out there that people are calling bigfoot, I think it more likely it is a feral and/or mentally ill human. That said, I cannot say bigfoots don't exist. See the difference? BTW, pretty sure unicorns don't exist either - but I can't prove it.

The OP has asked a very straightforward question - should pin 17 be connected to main ground on the motherboard or not.

Exactly. But you didn't answer that. You have the OP chasing components he may or may not have, posting illustrations of motherboards the OP does NOT have and we don't even know what symptoms the OP is experiencing - other than the computer will not power on.

You've been making assumptions based on zero information. You assumed and decided the OP meant "VGA ground plane" when what he said was "VGA plate". A plate in computers is typically a square or rectangular, flat piece of metal that mounts behind the motherboard for added support. That is totally different than a ground "plane". Did he mean ground? Maybe. But we don't know!

His problem points to a failed PSU. The OP said he tested his. How? We don't know. Most users do not have the proper tools or technical knowledge to conclusively test a PSU. But good power needs to be verified so he needs to swap in a known good PSU to see what happens.

But you seem focused on optocouplers. How does explaining what an optocoupler does, which the OP may or may not even have, help fix the OP's computer?

ShrimpBrime is right. We need more information about the system at hand. At least 7 times, the need for more information has been suggested by just about everyone - but you, qxp.

In order to actually help the OP fix the problems he's having with his computer (typically why folks come to TPU) we need to know what problems and symptoms he is experiencing. All we know at this point is the PC will not power on. I highly "doubt" a failed optocoupler on a ground pin, "IF" one exists, would cause that.

You clearly have some knowledge of electronics and that's great. But understand TPU is full of true experts with vast knowledge and experience in all sorts of areas within IT - which in itself, is industries within industries. The way to impress is by us helping people, not demonstrating our knowledge. But in order to help people, we need to understand their problem, first.

To do that here, we need more information.

 

[eidairaman1]

Break it up you 2

 

[Bill_Bright]

Break it up you 2

Already moved on - just waiting for OP to provide some more information so we can help them help themselves with their not-booting problem.

 

[Jaegar]

Indeed I used the paper clip method to test the psu, don't have any other testers. Currently don't have access to another psu I can test, but will try to secure one

My understanding of the OP post is that he/she tried to verify ground power connector connection by measuring continuity to a ground plane of the VGA card because it was easy to access. What OP found that all the ground pins of the motherboard connector except one - pin 17 - show continuity to VGA ground plane, as you would expect as PCI/PCIe connector has ground pins. The OP question is why is pin 17 not showing continuity even though it is marked ground on the spec. One possible reason is that the connection is poor, but it is more likely the motherboard was designed with pin 16 and pin 17 having a separate circuit that is activated with an optoisolator, or something similar that separates grounds.

The reason they did it is that specification calls for power supply pins 16/17 being safe to prevent high voltage reaching the case and/or power button in case of a fault. An optoisolator adds a bit to cost of the motherboard, but is a simple means to make the motherboard safe as well.

Thank you. This is what I wondering about because pin 17 doesn't register continuity like the rest of the ground pins

 

[ty_ger]

The OP has asked a very straightforward question - should pin 17 be connected to main ground on the motherboard or not. They did not ask for any advice on what to plug in. Just yes or no answer or some information to figure it out. Does your motherboard have pin 17 connected to main ground ? My motherboards don't have this connector, as I got Dell's 5820s and 7920s, so I can't test myself.

I don't think so. Pin 17 is part of the power-on signal circuit to the PSU. It and pin 16 act like a switch. There is no reason why that side of the switch would need to be grounded or carry ground current.

 

[ShrimpBrime]

Here is a 24 pin circuit diagram for an MSI MS-7540. This may not be a direct representation to the B450 motherboard, but won't be much different as far as grounds are concerned.

Hope this helps.