Question about 85c caps vs. 105c caps

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Not too many Electrolytic fail dead open or dead short.
It's usually a partial failure.
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[severach]

Re: Question about 85c caps vs. 105c caps

Electrolytic mostly fail open. Tantalum and ceramic fail shorted. There are a lot of places that an open is tolerated that a shorted won't be.

[PeteS in CA]

Re: Question about 85c caps vs. 105c caps

I've seen PCBs that were destroyed by the sudden catastrophic failure of both solid tantalum capacitors and large form factor SMT monolythic ceramic capacitors (which are EVIL!).

I wonder if lytics are unique in having a gradual failure mechanism, the drying out of the electrolyte. Thinking out loud ... film X and Y capacitors can take hits and self-heal over time, with the carbon residue forming conduction paths, eventually enough such paths to overheat and destroy the capacitor (though it probably will look to the user like a sudden catastrophic failure).

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

I've had high quality caps (OSCON) explode with no warning - but that's REALLY rare.
.
I -have- seen a board not boot at all due to two 22uF caps.
They (being bad) threw off the Vtt voltage to the chipset.
Not common but it happens...
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[Wester547]

Re: Question about 85c caps vs. 105c caps

Sorry, I don't mean to try anyone's patience. In reference to your answer, it reassures me, as everything else has in this thread. I'll leave the questions at that. And I understand that there are too many kinds of issues and different kinds of circumstances to give an absolute prediction of what will or won't happen (hardware failures aren't predictable, anyway), I was just contemplating. And I thought capacitors failed gradually, though I suppose it can be either instantaneous or gradual (or a mingling).

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Wouldn't one dead capacitor on the motherboard mean a dead motherboard? Or would the problem take longer than that to manifest itself as such? Or are there exceptions?

You keep asking for definitive answers to -very- generalized questions.
That is getting annoying particularly when the answers have already been discussed at least once right in this thread.
~ There ain't no magic pill or 'rule' that is -always- true.
~ Just isn't. - Have to look at it case by case.


This question is like asking: "If a wire gets 'damaged' my car won't 'run', right?"
-
Cars have lots of wires and they do different things.
Same with caps on mobos.
And words like 'damaged' and 'dead' can mean numerous different things.
Does 'dead' mean open? short? or out of spec?


To the question.
~~
It can but most of the time it won't.
Depends on what THAT cap does and what 'dead' means.
.
An open cap is like there isn't one there at all.
A shorted cap is like replacing the cap with a wire.
The result is different.
And MOST caps only partially fail which is enough to cause ill effects. - Partial short or partial ground.
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Lets say it's in the +5v rail.
There are usually several caps in parallel on +5v scattered about the board so if [only] one opens all you'll get is slightly more Ripple in +5v.
The affect will depend on whether or not the added Ripple is enough to be a problem or not on THAT board.
- If that same cap shorts instead of opens you'd have a dead board for sure.
That is connecting +5v straight to ground.
Fair chance the PSU or board traces will go up in smoke with that one.

Most caps fail gradually so there is an unstable period before it's actually 'dead'.
Depending on what's going on that period might be a few hours or years.
.
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Small lytic caps might be for surge suppression [connect/disconnect external cables], for EMI, for Ripple [at the output of small local regulators], or to do mundane jobs for things like sound.
They don't usually have helpers in parallel so when they're gone they're gone.
One for EMI or suppression that opens isn't likely going do squat as far as the board booting or running.
One for a small regulator for some chip's [or a chipset] voltage might prevent boot, cause BSOD, erratic operation or boot-loops.
.
The bigger caps might be to handle ripple for the rails, for larger local regulators, are used in the VRM (which is actually a complete but simple SMPS all by itself).
They also play a major part in keeping the board running during power fluctuations like mini back-up power supplies that are good for a few milliseconds.
With the exception of those in local regulators these usually have buddies in parallel to help out. That's great if one opens but others in parallel can't fix a short.
.
.

[Wester547]

Re: Question about 85c caps vs. 105c caps

Wouldn't one dead capacitor on the motherboard mean a dead motherboard? Or would the problem take longer than that to manifest itself as such? Or are there exceptions?

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Well, I'd rather not set mine to spin down at all (to be honest). But I should be more clear as to why I'm asking:

I want to reduce the heat output in the system by spinning down the second and hottest HDD in there (ST3160023A). Doing that has shown amelioration in temperature for the components, judging by the temperature sensors. Usually, you would have to spin it up and down in order to do that, but I tricked Windows XP into keeping it spun down once I spin it down by disabling the drive in device manager after I set the idle timer in HDD Scan (I set it to 30 seconds to give me enough time to do that). Then it just powers off after being spun down rather than ever spinning back up until next I boot up the computer. What I want to know is, is such an abrupt speed change a problem for the hard drive after only a few minutes of spinning up (as it naturally spins up when the system is powered on), as otherwise it would just be spinning (uninterrupted) for a few hours until power down?

I guess it would be more wear, but since I'm more worried about the temperatures of the board and capacitors, I may as well leave it like that (the ST3160023A runs rather warm for a HDD, since I have no extra airflow over the HDDs). I'm only keeping the drive in there because it has an installation of Windows that still has data on it itself.

A hard drive is a whoppin' 15-20 watts.
Just add a fan.
.

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Based on the info in this thread of discussion, it's also quite possible for the original, faulty PSU to be the culprit with regard to the dead CMOS battery, right?

Not likely.
More likely a small mobo cap.
Even more likely the battery is just worn out or you bought a bad one.
They have a shelf life too...
.

[Wester547]

Re: Question about 85c caps vs. 105c caps

Based on the info in this thread of discussion, it's also quite possible for the original, faulty PSU to be the culprit with regard to the dead CMOS battery, right?

[Wester547]

Re: Question about 85c caps vs. 105c caps

Well, I'd rather not set mine to spin down at all (to be honest). But I should be more clear as to why I'm asking:

I want to reduce the heat output in the system by spinning down the second and hottest HDD in there (ST3160023A). Doing that has shown amelioration in temperature for the components, judging by the temperature sensors. Usually, you would have to spin it up and down in order to do that, but I tricked Windows XP into keeping it spun down once I spin it down by disabling the drive in device manager after I set the idle timer in HDD Scan (I set it to 30 seconds to give me enough time to do that). Then it just powers off after being spun down rather than ever spinning back up until next I boot up the computer. What I want to know is, is such an abrupt speed change a problem for the hard drive after only a few minutes of spinning up (as it naturally spins up when the system is powered on), as otherwise it would just be spinning (uninterrupted) for a few hours until power down?

I guess it would be more wear, but since I'm more worried about the temperatures of the board and capacitors, I may as well leave it like that (the ST3160023A runs rather warm for a HDD, since I have no extra airflow over the HDDs). I'm only keeping the drive in there because it has an installation of Windows that still has data on it itself.

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Read the previous post again.
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[Wester547]

Re: Question about 85c caps vs. 105c caps

But is it bad to say.... start the system, then a few minutes after, spin the hard drive down and keep it spun down (instead of keeping it spinning for the whole duration of use, keep it spinning for a few minutes then spin it down until it spins up again during the next restart)? Is such an abrupt speed change any sort of issue for the bearings and spindle motor? ^^;

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

If you leave it spun up it eats more power and stays at a higher temp.
.
Spinning it up and down does cause more wear than constant speed.
And spinning fast is more wear than spinning slow.
And two hairs weigh more than one hair too.
- Point is 'more' doesn't necessarily mean 'significant'.

I usually set mine to spin down after 15-20 minutes.
If I'm not doing anything for that long it usually means I wandered off to do something else.
I do that for power use and heat though, not bearings.
.

[Wester547]

Re: Question about 85c caps vs. 105c caps

I guess my question more limpidly was, is it better to keep a hard drive constantly spinning, or is it any worse to spin it up for a few minutes (what turning on the system does) then keep it spun down until the system restarts? From what I garner, they're designed to do it either way without consequence. But...

Then there is a time-out that spins it down to an idle speed after x-many minutes of not being used.
[That time is what you can usually adjust in BIOS or sometimes in the OS.

Is this something like advanced power management levels? I thought a hard drive couldn't spin at anything less than its full rotation rate without spinning down. Is speed change more stressing to the hard drive than keeping it spinning at its rotation rate? That is, speed change (spin down) within a few minutes of starting the drive after a while (but again, without spinning it back up).

And I'm guessing hard drive heat doesn't have much on capacitors, right (hard drives that have no fan blowing over them)?

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Like I said, old school +5V TTL.

Granted that I went further afield, noise is noise, whether it comes from inadequately filtered P/S ripple, or inadequately decoupled ICs. In some ways the latter can be nastier, as it might not be visible with an oscilloscope.

Agreed but it's better to explain one thing at a time and the core question was: how can a PSU issue screw up a hard drive.
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[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

^ So, I'm guessing mechanical disk drives like to spin up, spin at a constant rotation rate for a while, then spin down? Spinning it up then spinning it down a few minutes later and some hours later, shutting it down after it spins down (but doesn't spin back up until next the system is booted) isn't great for the drive? And well, as far as airflow goes, I was just wondering if having part of an IDE (or in this case, a PATA) cable touching part of the second RAM module would hinder airflow significantly, especially since the two capacitors are near it.

That's a lot of spins. Now my head is spinning.
.
The RPM is controlled by the firmware and there are various schemes in use.
Usually BIOS's have settings that can over-ride some of it.
.
The simplest scheme is to spin the drive up to full speed when it's needed.
Then there is a time-out that spins it down to an idle speed after x-many minutes of not being used.
[That time is what you can usually adjust in BIOS or sometimes in the OS.]
.
With drive bearings and wear you are really worrying about something that isn't worth worrying about much.
It's not like you can swap them for better bearings.
You get what you get.
And they are made of materials that last for eons.
- I think it's Stellite which is a cobalt-chromium alloy.
- Very hard, very heat resistant, used in 'cobalt' drill bits.
You are more likely to blow a chip than a bearing.
.

[PeteS in CA]

Re: Question about 85c caps vs. 105c caps

I was actually thinking of [a fairly modern] CPU when I picked 1.5v volts.

Like I said, old school +5V TTL.

Granted that I went further afield, noise is noise, whether it comes from inadequately filtered P/S ripple, or inadequately decoupled ICs. In some ways the latter can be nastier, as it might not be visible with an oscilloscope.

[PCBONEZ]

Re: Question about 85c caps vs. 105c caps

Thanks for the diagrams, PCB. As the saying goes, "A picture is worth ...". The thresholds I would have used, had I gone to that level of detail, would have been the thresholds for old-school +5V TTL. One extra wrinkle to add to your diagram, some noise goes below the 0V level. And if it goes sufficiently negative such spikes can have their own interesting effects. And another wrinkle, if the noise goes sufficiently high in the positive direction, some protective components in the IC become active, protecting the IC, but possibly affecting the speed. Since digital ICs are synchronized by clocks, the ICs' changing state can generate quite a bit of noise. The state change is not instantaneous, and for some 10s or 100s of picoseconds, each data output line can draw quite a bit of current. Large pulses of current plus stray inductances and capacitances can be a very noisy combination.

The rise time doesn't have much to do specifically with Ripple corrupting a signal which was the point of the drawing.

Like I said that was quick and dirty. I used MS Paint.
If you wanna do up a prettier more detailed one then go right ahead. {I'll look...}

120mV Ripple is the ATX 12v spec. That's why I chose it.
With 5v signaling 120mV ripple isn't that big a deal because there's a lot of room to the threshold.
- Which is why old Mobo/CPU's like 486 that used 5v signaling for everything didn't need scads of low ESR caps.
5v signaling would be harder to show the Ripple related problem and it isn't used that much on mobos anymore anyway.
AGP was down to 0.8v before it faded out.
PCI can be either 5v or 3.3v but, while add-in cards are often 5v, onboard chips on the PCI BUS are most always 3.3v.
DDR2 uses 1.8v
Chipsets use a sundry of signal voltages down to at least 1.5v
.
I was actually thinking of [a fairly modern] CPU when I picked 1.5v volts.
More or less a random pick of legit values that would show what I wanted to show.
.
.

[Wester547]

Re: Question about 85c caps vs. 105c caps

^ So, I'm guessing mechanical disk drives like to spin up, spin at a constant rotation rate for a while, then spin down? Spinning it up then spinning it down a few minutes later and some hours later, shutting it down after it spins down (but doesn't spin back up until next the system is booted) isn't great for the drive? And well, as far as airflow goes, I was just wondering if having part of an IDE (or in this case, a PATA) cable touching part of the second RAM module would hinder airflow significantly, especially since the two capacitors are near it.