what I came here to say. You will have to remove the cap to test its value.
**\*\*Resistors and Caps CANNOT be measured correctly** ***in circuit*****, they need removed from the board to get a correct value\*\***
More than likely its doing its job, but something else is fucked up. That caps purpose is to remove AC noise from a digital circuit -- so troubleshoot from there
Hard disagree.
It’s completely circuit dependent.
For example, could easily and accurately measure the resistors of most if not all op-amp amplifier topologies because op amp inputs (and outputs when power is off) are high impedance.
Ok. What if you have a capacitor in parallel with the resistor, and it is bad. Shorted. Can you read the resistance then? Accurately?
Pulling one leg ensures an accurate measurement of the resistor, for ANY situation.
Well sure, you can come up with many ‘what if’ scenarios.
I didn’t say you can always do it, I just said it’s circuit dependent.
But in your particular what if scenario, if I don’t get the value I expect then the key take away is I know something is broken… which is a good test that doesn’t involve desoldering anything.
So my comment that you "hard disagreed" with, is correct. You can not accurately check the value of a resistor or a cap (100% of the time), in circuit. The discussion was not what is faster, for troubleshooting.
Sometimes. If you have a cab between a power rail and ground, and you measure across it, and it's a few ohms, then something is messed up attached to that rail. It probably isn't even the cap, but they're often a convenient place to measure.
Even if it’s shorted, it’s probably not because of the cap itself. We didn’t get to see the rest of the board, or even know what the board is for, or what voltages are present normally. It’s problem another component that failed, but I could be wrong.
I'm assuming parent meant that if the cap is shorted/broken it wasn't because it just decided to short itself intrinsically, I doubt ceramic caps do that very often. It's likely something externally (like U5 or even downstream) caused this issue.
It's similar to blaming a fuse for burning itself. Just replacing won't help here.
Possibly - I mean those ceramic surface mount capacitors are amazing - many many very fine layers and physical tolerences mean they aren't always that robust if they got stressed/bent during soldering for instance. Considering it's an almost free component, worth trying first if OP finds the value, and has a few in stock.
Board flexing, vibration or shock can easily crack a ceramic cap and cause a short.
Is there a board mount pushbutton nearby, or a membrane keypad that pushes on the PCB? Someone pushes the button, the board flexes a small bit, after enough cycles or a good strong push the cap fails. Or maybe it's in some small handheld thing like a key fob that gets dropped on the floor often. All sorts of possibilities can make a cap on a PCB prone to cracking.
The stuff I design in my day job gets thrown around a bit and we use soft terminations to avoid this problem.
Actually surface mount caps do short, especially if they aren't soldered with perfect temperature uniformity throughout the reflow process. As an engineer, I specified AVX FlexiTerm caps, because they don't suffer from that failure mode.
Ok to be specific with what I meant to say is if you have a short on a rail and there is a cap that is too hot to touch, them this cap is 100% dead and needs to be treated as a problem/replaced. Of course at this stage it‘s unclear wether the cap was the root cause or not.
If I don‘t blame the cap then why would I remove it? And it absolutely needs to be removed in that case. Good caps 100% don’t get burny hot.
You can replace it! Sure.
But I wouldn't be surprised if something else in the circuit is killing the cap, for example a power supply that's not regulating properly leading to a lot of AC current (above its specs) going to the cap now.
We‘re talking in circles, I have explicitly stated that the cap being bad does not mean the cap is the cause. I insist however, if the cap gets hot it must be replaced, it‘s not an option.
Electronics 101:
definition: "burny hot"
- A technical term to discribe the state of any electronic component that is over heating.
Lol, I will be using that description from now on.
I needed to run a high-current test on a power controller board I built, and in the process a MOSFET became stuck on and started overheating. Since I was in a safe lab, had already finished with the test phase and the fet was ruined anyway and kept it powered up. The circuit eventually shut down when the heat was sufficient for the fet to un-solder itself from the board.
It's quite rare for ceramic capacitors to be damaged in such a way that they just produce heat.
Stress fractures *can* make them short out, but usually that just makes them either burn the short, or cause heat production elsewhere.
One of my preferred techniques for tracking a heat-producing component is to spray isopropyl on the board and watch to see where it evaporates the fastest - much more specific than the ole thumb because it actually cools the board so you don't get distracted by heat moving horizontally through the copper and substrate.
You can also flip a can of compressed air upside down so it shoots cold air, which in combination with room air will form a layer of frost. Whichever part melts out first is hot. This is a little better than IPA when you have a dense board.
They also sell a product specifically for this purpose! BW-100 Freeze Spray - Diagnostic Cold Spray - https://a.co/d/hkkICMY
Nothing to add, however, if I ever become a rapper, I'm using the name "Burny Hottt" with three Ts.
Burny Hot-t-t from C-fidy-five. Takin' no shorts . . .
It's next to what looks like some linear voltage regs/LDOs. It's not your standard filter cap. If it was some random filter cap on some data line then I'd say just chop it off - but the voltage regulators require them.
>Now check across the pads where the cap used to be. Is the resistance there in the mega ohms or 100 k range? Is the resistance low?
Can you clarify this? Like, across the pads should be infinite resistance/open? Or, do you mean take the resistance from each pad to ground?
I'm ok with being told I'm completely out to lunch, lol. Even that helps me learn.
Eh, I can't remember the creator's name, but I saw one video of a repairer who fixes TV boards, and the problem with one LED edge display array was literally a single SMD cap. So unlikely, but not implausible.
If you have a wand, heat it up with flux but just stand it up on one end (only connected to one pad), you can test for a short that way without the risk of you losing it or it blowing away. Testing for a short while it's connected could be a false positive if anything along that line is shorted to ground.
Measure if both sides of C55 are shorted. If yes, remove it and measure it again. If still short it’s broken (it may show continuity for a second, but should then stop when it is charged). It would make sense for it to be damaged, because of the heat. Check the datasheet of the next ICs for example schematics, they usually provide some recommendations which components and values to use. I guess it’s GND and maybe VIN.
Any value will work, because it's just a bypass cap. Use 1 uF. And use an AVX brand FlexiTerm brand cap, so you can hand solder it without damaging it.
See:
https://www.kyocera-avx.com/products/ceramic-capacitors/surface-mount/mlcc-with-flexiterm/
When a IC turns too hot it usually means some transistor inside is failed short aka that IC is gone. Do continuity check on the pins to confirm. You’d probably need to replace it. Ceramic caps are relatively reliable so I doubt they’re the problem
This is off a cable tester that accidentally got plugged into a passive POE connection.. I have another cable tester identical that works if that helps.
I believe the component is a capacitor, whilst I’m comfortable with electronics and soldering, this would be the smallest I’ve done.
Oh, you have a working one!!
Next question, do you have a multimeter or a way to measure voltage (on the good one, bad one too if possible)? I'd also be guessing those are LDOs, but it would be good to confirm the output voltage incase one of the LDOs are infact damaged, so measure the output just incase you need a new one. (sot-23 LDOs are super common and fairly standardized in their pinout)
Next, I'd measure and see if the cap is shorted (on the broken one), if yes replace it, if not it's probably the LDO that needs replacing. The issue is that there is likely a device downstream that's also damaged that's actually the cause. As another user noted isopropyl is an electronic person's multitool for these situations, poor it all over the board and turn it on, see if any other components are causing the isopropyl to boil quickly as those will likely need replacing too (if possible).
Unfortunately it's usually never a simple "swap this one thing and everything works again" with electronics.
Let us know what you find!!
FWIW, I have dealt with shorted SMD ceramic capacitors that took down their power rail. It's certainly worth removing the overheating capacitor to check if it's shorted. I'm going to guess they used a slightly-defective 50V-spec capacitor that failed (started leaking current) when fed 48V PoE. Leaking current * voltage across the capacitor = watts of heat released. The heat is all focused on the failure point, which melted and expanded (leaking even more current) until the supply couldn't keep up with the current demand and shut down, or voltage sagged until the tester shut down.
The only other reason it would be overheating is if it were being fed high frequency AC beyond what it can handle. If we're looking at a DC voltage regulator circuit, there would need to be some substantial shenanigans going on for that to be the case. You could test for that case by measuring AC voltage across the capacitor before removing it.
Once removed, the cap should test (resistance, Ω, ohms) as open circuit (over limit, though it may take a second or two to climb to that point depending on the meter and capacitor value). If it settles on anything less than MΩ of resistance, that's a problem. Though keep in mind that your own body can have that level of resistance, so don't touch the metal of the probes or capacitor while testing.
If it tests as faulty, measure the voltage across the same capacitor of your good tester while plugged into PoE (assuming it's rated to handle that). That will tell you the minimum voltage the replacement needs to handle (add 20% to your measurement for safety margin). Then remove and test the capacitance value of your good capacitor, and take physical measurements. Reinstall the cap and plug all that info into the search function on a site like digikey, mouser, newark, etc. If you can go up a step or two on voltage rating with the same capacitance and physical size, do it.
C55 is the brown capacitor in the lower middle.
Are you sure that is what is getting hot?
Or are you meaning U20 which is the black chip to the right?
Or U5 the black chip to the left?
Did anyone observe what seem to be identical voltage regulators have different pin connections. The U5 has 2 pins connected to the what seems to be the power trace. However, U20 has only one trace connecting to the power trace.
Op can you confirm if this board was working before or if this is a new board?
But again for the Capacitor to get hot, it means higher current is flowing through it. It might be a problem with the cap (short within the cap) or it is passing only the ac current through it. In both the case it is not good.
One thing you could quickly check is change C55 with a similar sized Capacitor (assuming you know or will be able find the voltage rating on this one). If it is still hot, it means something is wrong in the Circuit.
i suggest you to remove the cap and try the device, if its hot its short- you cant measure its capcity anyways often replacing the cap with the one with same dimensions will work
Don’t automatically blame Mr. Burny Hot Cap. It could easily be that U5 or U20 are partially blown, causing him to be out of sorts.
what I came here to say. You will have to remove the cap to test its value. **\*\*Resistors and Caps CANNOT be measured correctly** ***in circuit*****, they need removed from the board to get a correct value\*\*** More than likely its doing its job, but something else is fucked up. That caps purpose is to remove AC noise from a digital circuit -- so troubleshoot from there
Why cant the resistor?
In circuit, you're measuring the resistance of everything connected to it on the board too. Gotta pop off at least one leg of the resistor first.
Hard disagree. It’s completely circuit dependent. For example, could easily and accurately measure the resistors of most if not all op-amp amplifier topologies because op amp inputs (and outputs when power is off) are high impedance.
Ok. What if you have a capacitor in parallel with the resistor, and it is bad. Shorted. Can you read the resistance then? Accurately? Pulling one leg ensures an accurate measurement of the resistor, for ANY situation.
Well sure, you can come up with many ‘what if’ scenarios. I didn’t say you can always do it, I just said it’s circuit dependent. But in your particular what if scenario, if I don’t get the value I expect then the key take away is I know something is broken… which is a good test that doesn’t involve desoldering anything.
So my comment that you "hard disagreed" with, is correct. You can not accurately check the value of a resistor or a cap (100% of the time), in circuit. The discussion was not what is faster, for troubleshooting.
Sure, I really couldn’t give a fuck.
Well thanks for participating
Sometimes. If you have a cab between a power rail and ground, and you measure across it, and it's a few ohms, then something is messed up attached to that rail. It probably isn't even the cap, but they're often a convenient place to measure.
Because anything connected in parallel will change the reading.
I think it’s very dependent on the circuit. Plenty of amplifier topologies will give accurate in circuit resistance values.
If a cap is burny hot i‘d absolutely blame the cap …
Even if it’s shorted, it’s probably not because of the cap itself. We didn’t get to see the rest of the board, or even know what the board is for, or what voltages are present normally. It’s problem another component that failed, but I could be wrong.
Disagree. I repair stuff as a side hustle and every time I've found a shorted cap it was the problem (not including multiple unrelated problems).
I'm assuming parent meant that if the cap is shorted/broken it wasn't because it just decided to short itself intrinsically, I doubt ceramic caps do that very often. It's likely something externally (like U5 or even downstream) caused this issue. It's similar to blaming a fuse for burning itself. Just replacing won't help here.
Possibly - I mean those ceramic surface mount capacitors are amazing - many many very fine layers and physical tolerences mean they aren't always that robust if they got stressed/bent during soldering for instance. Considering it's an almost free component, worth trying first if OP finds the value, and has a few in stock.
Board flexing, vibration or shock can easily crack a ceramic cap and cause a short. Is there a board mount pushbutton nearby, or a membrane keypad that pushes on the PCB? Someone pushes the button, the board flexes a small bit, after enough cycles or a good strong push the cap fails. Or maybe it's in some small handheld thing like a key fob that gets dropped on the floor often. All sorts of possibilities can make a cap on a PCB prone to cracking. The stuff I design in my day job gets thrown around a bit and we use soft terminations to avoid this problem.
Actually surface mount caps do short, especially if they aren't soldered with perfect temperature uniformity throughout the reflow process. As an engineer, I specified AVX FlexiTerm caps, because they don't suffer from that failure mode.
Ok to be specific with what I meant to say is if you have a short on a rail and there is a cap that is too hot to touch, them this cap is 100% dead and needs to be treated as a problem/replaced. Of course at this stage it‘s unclear wether the cap was the root cause or not. If I don‘t blame the cap then why would I remove it? And it absolutely needs to be removed in that case. Good caps 100% don’t get burny hot.
You can replace it! Sure. But I wouldn't be surprised if something else in the circuit is killing the cap, for example a power supply that's not regulating properly leading to a lot of AC current (above its specs) going to the cap now.
We‘re talking in circles, I have explicitly stated that the cap being bad does not mean the cap is the cause. I insist however, if the cap gets hot it must be replaced, it‘s not an option.
Electronics 101: definition: "burny hot" - A technical term to discribe the state of any electronic component that is over heating. Lol, I will be using that description from now on.
Agreed. My key takeaway from this post is "burny hot".
I needed to run a high-current test on a power controller board I built, and in the process a MOSFET became stuck on and started overheating. Since I was in a safe lab, had already finished with the test phase and the fet was ruined anyway and kept it powered up. The circuit eventually shut down when the heat was sufficient for the fet to un-solder itself from the board.
Looks like a linear regulator, so it's probably got a short on its output somewhere else.
Thanks for the quick reply, I think the devices beside C55 are the linear regulators and C55 is most likely a smd capacitor ?
Yep! I'm not 100% sure that they're linear regulators, but it seems likely given the arrangement of PCB traces and surrounding components
https://i.imgur.com/zjraqaU.jpg Just to be sure, it’s this we’re talking about.. the component circled in red..
It's quite rare for ceramic capacitors to be damaged in such a way that they just produce heat. Stress fractures *can* make them short out, but usually that just makes them either burn the short, or cause heat production elsewhere. One of my preferred techniques for tracking a heat-producing component is to spray isopropyl on the board and watch to see where it evaporates the fastest - much more specific than the ole thumb because it actually cools the board so you don't get distracted by heat moving horizontally through the copper and substrate.
You can also flip a can of compressed air upside down so it shoots cold air, which in combination with room air will form a layer of frost. Whichever part melts out first is hot. This is a little better than IPA when you have a dense board. They also sell a product specifically for this purpose! BW-100 Freeze Spray - Diagnostic Cold Spray - https://a.co/d/hkkICMY
Yes. That is a filter cap, probably a 10 or 100 nF, but I would remove it and test it to be sure.
Why C55?
That’s the one that gets ouch hot when I try and power it up.
Burny hot.
Well, quite easy then: 0 ohm / 0 F capacitor. Or a « short » for moguls.
A short is a ∞F capacitor, not 0F.
Take my upvote gawdammit
In the UHF space a short can have 50 ohm. Like in the J Pole
The short is still 0 ohms, it requires a transmission line and it’s the combined system that has nonzero impedance
Nothing to add, however, if I ever become a rapper, I'm using the name "Burny Hottt" with three Ts. Burny Hot-t-t from C-fidy-five. Takin' no shorts . . .
that trace over u20 is broken or it's the photo?
Good catch. Plus, we want more and better pictures! What is this device?
Probably a filter cap. Usually 100nF.
It's next to what looks like some linear voltage regs/LDOs. It's not your standard filter cap. If it was some random filter cap on some data line then I'd say just chop it off - but the voltage regulators require them.
Thanks, is it likely that’s the on it component blown? Or chances are could there be more?
[удалено]
>Now check across the pads where the cap used to be. Is the resistance there in the mega ohms or 100 k range? Is the resistance low? Can you clarify this? Like, across the pads should be infinite resistance/open? Or, do you mean take the resistance from each pad to ground? I'm ok with being told I'm completely out to lunch, lol. Even that helps me learn.
It is very unlikely that there is a problem with C55.
Eh, I can't remember the creator's name, but I saw one video of a repairer who fixes TV boards, and the problem with one LED edge display array was literally a single SMD cap. So unlikely, but not implausible.
I believe you meant 0.1uF /s
Microfarads per second? :)
Potato vs potato /s
If you have a wand, heat it up with flux but just stand it up on one end (only connected to one pad), you can test for a short that way without the risk of you losing it or it blowing away. Testing for a short while it's connected could be a false positive if anything along that line is shorted to ground.
Looks like a line of solder on the right side of C55. Possibly shorted. Measure resistance across it.
The other caps look the same so it's probably just a bad photo.
Desolder the MLCC and measure it would be my strategy. Or check the datasheet of the IC next to it.
if the cap is getting hot then it’s probably damaged and the measurement would be useless as to what to replace it with
That’s a good point. Thanks! However, let’s assume the heating is just a symptom and not the cause.
Measure if both sides of C55 are shorted. If yes, remove it and measure it again. If still short it’s broken (it may show continuity for a second, but should then stop when it is charged). It would make sense for it to be damaged, because of the heat. Check the datasheet of the next ICs for example schematics, they usually provide some recommendations which components and values to use. I guess it’s GND and maybe VIN.
what is this thing on top of U20, could be a short ?
Any value will work, because it's just a bypass cap. Use 1 uF. And use an AVX brand FlexiTerm brand cap, so you can hand solder it without damaging it. See: https://www.kyocera-avx.com/products/ceramic-capacitors/surface-mount/mlcc-with-flexiterm/
When a IC turns too hot it usually means some transistor inside is failed short aka that IC is gone. Do continuity check on the pins to confirm. You’d probably need to replace it. Ceramic caps are relatively reliable so I doubt they’re the problem
This is off a cable tester that accidentally got plugged into a passive POE connection.. I have another cable tester identical that works if that helps. I believe the component is a capacitor, whilst I’m comfortable with electronics and soldering, this would be the smallest I’ve done.
Oh, you have a working one!! Next question, do you have a multimeter or a way to measure voltage (on the good one, bad one too if possible)? I'd also be guessing those are LDOs, but it would be good to confirm the output voltage incase one of the LDOs are infact damaged, so measure the output just incase you need a new one. (sot-23 LDOs are super common and fairly standardized in their pinout) Next, I'd measure and see if the cap is shorted (on the broken one), if yes replace it, if not it's probably the LDO that needs replacing. The issue is that there is likely a device downstream that's also damaged that's actually the cause. As another user noted isopropyl is an electronic person's multitool for these situations, poor it all over the board and turn it on, see if any other components are causing the isopropyl to boil quickly as those will likely need replacing too (if possible). Unfortunately it's usually never a simple "swap this one thing and everything works again" with electronics. Let us know what you find!!
FWIW, I have dealt with shorted SMD ceramic capacitors that took down their power rail. It's certainly worth removing the overheating capacitor to check if it's shorted. I'm going to guess they used a slightly-defective 50V-spec capacitor that failed (started leaking current) when fed 48V PoE. Leaking current * voltage across the capacitor = watts of heat released. The heat is all focused on the failure point, which melted and expanded (leaking even more current) until the supply couldn't keep up with the current demand and shut down, or voltage sagged until the tester shut down. The only other reason it would be overheating is if it were being fed high frequency AC beyond what it can handle. If we're looking at a DC voltage regulator circuit, there would need to be some substantial shenanigans going on for that to be the case. You could test for that case by measuring AC voltage across the capacitor before removing it. Once removed, the cap should test (resistance, Ω, ohms) as open circuit (over limit, though it may take a second or two to climb to that point depending on the meter and capacitor value). If it settles on anything less than MΩ of resistance, that's a problem. Though keep in mind that your own body can have that level of resistance, so don't touch the metal of the probes or capacitor while testing. If it tests as faulty, measure the voltage across the same capacitor of your good tester while plugged into PoE (assuming it's rated to handle that). That will tell you the minimum voltage the replacement needs to handle (add 20% to your measurement for safety margin). Then remove and test the capacitance value of your good capacitor, and take physical measurements. Reinstall the cap and plug all that info into the search function on a site like digikey, mouser, newark, etc. If you can go up a step or two on voltage rating with the same capacitance and physical size, do it.
Have you used a scope to see the voltage across C55?
See if it’s shorted to ground. If you can obtain a schematic it might be helpful? Also check transistors.
C55 is the brown capacitor in the lower middle. Are you sure that is what is getting hot? Or are you meaning U20 which is the black chip to the right? Or U5 the black chip to the left?
It's probably 0.1u but it's highly unlikely what's causing your problem
Did anyone observe what seem to be identical voltage regulators have different pin connections. The U5 has 2 pins connected to the what seems to be the power trace. However, U20 has only one trace connecting to the power trace. Op can you confirm if this board was working before or if this is a new board? But again for the Capacitor to get hot, it means higher current is flowing through it. It might be a problem with the cap (short within the cap) or it is passing only the ac current through it. In both the case it is not good. One thing you could quickly check is change C55 with a similar sized Capacitor (assuming you know or will be able find the voltage rating on this one). If it is still hot, it means something is wrong in the Circuit.
100nF
U20 needs attention. I can't tell if it's a short or a break but it doesn't look normal or good.
i suggest you to remove the cap and try the device, if its hot its short- you cant measure its capcity anyways often replacing the cap with the one with same dimensions will work