Capacitor

  • Thread starter Thread starter Frank
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Frank

Hello,

perhaps this is dumb, but I do not know an answer.

I got 2 machines at work which work like a charm. No hangups, no bluescreen.
Perfect.

Now as I opened them for cleaning I noticed 2 capacitors with brown crusting
on the top. Seems as they had those for a little while. Nowhere else was the
crusting and it has dried.

Now my question is: The machines work, without a flaw, beleve it or not. Do
I have to change the mobo´s (boards) or can I stick with the present ones?
Like never change a running system?

Thanks for any advice-
 
| Hello,
|
| perhaps this is dumb, but I do not know an answer.
|
| I got 2 machines at work which work like a charm. No hangups, no
bluescreen.
| Perfect.
|
| Now as I opened them for cleaning I noticed 2 capacitors with brown
crusting
| on the top. Seems as they had those for a little while. Nowhere else
was the
| crusting and it has dried.
|
| Now my question is: The machines work, without a flaw, beleve it or
not. Do
| I have to change the mobo´s (boards) or can I stick with the present
ones?
| Like never change a running system?
|
| Thanks for any advice-
|
|

Typically, an electrolytic capacitor (a metal cylindrical can with a
rubber plug in one end, and 2 leads protruding out of the rubber plug)
will leak at the end where the rubber plug or seal is inserted.
Additionally, when they go bad, oftentimes an electrolytic capacitor
will "bulge" on top due to the internal pressure generated when the
cap got to hot and the electrolyte therein vaporized thus causing
extreme pressure to buildup internally. Perhaps if you can post a
picture on the net, informed users could comment. It is rather
unusual for a cap to allow fluid to leak out the "metal" side of the
can, tho I suppose anything is possible.
 
Typically, an electrolytic capacitor (a metal cylindrical can with a
rubber plug in one end, and 2 leads protruding out of the rubber plug)
will leak at the end where the rubber plug or seal is inserted.
Additionally, when they go bad, oftentimes an electrolytic capacitor
will "bulge" on top due to the internal pressure generated when the
cap got to hot and the electrolyte therein vaporized thus causing
extreme pressure to buildup internally. Perhaps if you can post a
picture on the net, informed users could comment. It is rather
unusual for a cap to allow fluid to leak out the "metal" side of the
can, tho I suppose anything is possible.
Click to expand...

First thanks for the reply, but is is exactly as you said it normally cannot
be.

On the top of the thingie, there are two curves in the metal cover where the
capacitor should break up if the pressure is too big. It seems that it broke
up, but only that far that a liitle amount of electrolyte came out like two
or three needle tops. This dried on the top, I think sealing it again. It
stands perfectly flat on the mobo, no rubber out or else, just a little
brown dried liquid on the top, really not more than 2 or 3 needle tops, or
heads, sorry I´m German, do not know the exact word for it.

Frank
 
Hello,

perhaps this is dumb, but I do not know an answer.

I got 2 machines at work which work like a charm. No hangups, no bluescreen.
Perfect.

Now as I opened them for cleaning I noticed 2 capacitors with brown crusting
on the top. Seems as they had those for a little while. Nowhere else was the
crusting and it has dried.

Now my question is: The machines work, without a flaw, beleve it or not. Do
I have to change the mobo=3Fs (boards) or can I stick with the present ones?
Like never change a running system?
Click to expand...

Caps, the ones you're talking about, filter ripples out of the power
signal and provide a stable (flat) voltage for the circuitry to use.

A cap that has bulged or busted, even around the "X" or "/" pattern on
the top is indeed defective. There are two things that commonly happen
to the circuit when this happens:

1) The filtering of the ripple is nullified and causes the voltage to
ripple which may or may not have an immediate impact on the system. It
is possible that the defective cap, if not shorted, will have no impact
on the system that you can see.

2) The cap, can short - meaning that it will cross the + and ground
lines and can burn the traces on the motherboard, can cause a section of
the board to stop working, and cause a small fire.

In any even the solution that first bubbles out of the cap is corrosive
and can, over time, even when it looks dry, can eat through traces on
the board - even when it looks dry it can absorb moisture out of the
air.

Replace the CAP as soon as possible or at least remove it.
 
air.
Replace the CAP as soon as possible or at least remove it.

--
Click to expand...

What do you mean? Remove the Cap of the capacitor or the whole capacitor? If
I remove the cap of the capacitor it will be open. I?m not good at
soldering, so I won?t be able to solder a new one onto it.
 
1) The filtering of the ripple is nullified and causes the voltage to
ripple which may or may not have an immediate impact on the system. It
is possible that the defective cap, if not shorted, will have no impact
on the system that you can see.
Click to expand...

Thinking again, the defective caps are near the AGP slot and the LCD
connected to the Geforce MX shows colour differencies in a solid colour
screnn. What I try to say is that the screen is divided into three section
that look like ribbons in slight different colour.

Could that behaviour be related to the caps?

I did not think of these effect because I thought it mitght be related to 8
hours use a day for 3 years now.
Is it obious these effects are leated? I must say that the LCD does not
chance if I chande brightness and contrast in the OSD of the LCD, so I think
it is a LCD problem and not related to the Mobo.


Frank
 
What do you mean? Remove the Cap of the capacitor or the whole capacitor? If
I remove the cap of the capacitor it will be open. I?m not good at
soldering, so I won?t be able to solder a new one onto it.
Click to expand...

There is no "CAP" on a capacitor - the term CAP means Capacitor in the
industry. What I was suggesting was, if you are not going to have it
replaced, then you would be better served my completely removing it,
cleaning the area with 99% alcohol. ALL POWER MUST BE REMOVED BEFORE
ATTEMPTING A DEVICE REMOVAL, not just turned off, actually remove the
power cord from the power supply, remove any device connections (modem,
monitor, scanner, USB devices....).

If you can't solder, if you can get near it, you could just clip the
leads (but I'm betting that you can't even see the leads).

You may get years of trouble free operation, or it may die in seconds,
it may short out and take the board with it, or the corrosive
electrolyte may eat through something.... In any case, I would remove it
at the very least and clean it.
 
Am Mon, 15 Nov 2004 21:11:46 +0100 schrieb Frank:

[Kondensatorenprobleme]
heads, sorry I´m German, do not know the exact word for it.
Click to expand...

Wenn du sowieso aus Deutschland kommst, antworte ich einfach auch mal auf
deutsch ;) Über kurz oder lang werden sich die geplatzten Kondensatoren
bemerkbar machen. Bei mir ist das System dann immer sporadisch eingefroren
(nach einem Reset lief es direkt wieder). Davon, die Kondensatoren selbst
auszutauschen, würde ich dir dringend abraten. Du machst mit an Sicherheit
grenzender Wahrscheinlichkeit mehr kaputt, als du reparierst (es sei denn,
du bist zufällig vom Fach). Solltest du noch Garantie haben: nichts wie hin
zum Händler und reparieren/tauschen lassen. Sollte normalerweise problemlos
über die Bühne gehen, da die Probleme mit den defekten Kondensatoren
mittlerweile wohl bei jedem Hersteller bekannt sind. Wenn nicht, arbeite
solange es geht mit dem Board weiter und tausch es gegen ein Neues aus,
sobald Fehler auftreten.

HTH

Gruß
Carsten
 
Leythos said:
Replace the CAP as soon as possible or at least remove it.
Click to expand...

Removing a cap from a switching power supply, where it is likely to belong,
might disable the board completely. I actually found a similar problem on my
old Aopen mobo (in my case the caps are definitely belong to the main CPU
switching power supply), so I went and bought a new ASUS mobo :) But I am
going to replace the caps on the old board and then build a second computer.

/MM
 
Removing a cap from a switching power supply, where it is likely to belong,
might disable the board completely. I actually found a similar problem on my
old Aopen mobo (in my case the caps are definitely belong to the main CPU
switching power supply), so I went and bought a new ASUS mobo :) But I am
going to replace the caps on the old board and then build a second computer.
Click to expand...

The onboard PSU is normally not a switching unit, the Switching PSU's
are the large metal units that you connect AC to. Most of the
"regulators" on the motherboard have no PSU to them, they are just
voltage regulators. A regulator, using the existing DC signal from the
PSU, uses the CAP's to clean the ripple out of the "switched" DC supply
from the PSU.

Removing a CAP, from the PSU would indeed cause problems, as they use
the caps to provide ripple rejection to the DC output.

The caps on a motherboard, in almost every instance, are to spot signal
filtering or for ripple rejection at the point.
 
Leythos said:
The onboard PSU is normally not a switching unit, the Switching PSU's
are the large metal units that you connect AC to. Most of the
"regulators" on the motherboard have no PSU to them, they are just
voltage regulators. A regulator, using the existing DC signal from the
PSU, uses the CAP's to clean the ripple out of the "switched" DC supply
from the PSU.
Click to expand...

This is completely wrong!!!! All of the modern high-current onboard PSUs
used in digital circuits are in fact switchers. The only place where you can
still find linear regulators these days are in sensitive analog electronics.
I am a board designer myself, so I know what I am talking about. A typical
mobo will have a bunch of coils near the CPU. That's where you have a hefty
switching regulator generating CPU core voltage/voltages. If they used a
linear regulator they would have to waste half of the power since core
voltages are so low and the lowest voltage available from the big PSU is
3.3V.

/MM
 
Frank said:
Now my question is: The machines work, without a flaw, beleve it or not.
Do I have to change the mobo´s (boards) or can I stick with the present
ones?
Click to expand...

Find someone who is handy with a soldering iron and get him (or her) to
change the capacitors. It isn't difficult (or expensive) if you know what
you are doing - but make sure the new capacitors are the same value as the
old ones and they are installed with the polarity (+ and -) the same.

Tom S
 
This is completely wrong!!!! All of the modern high-current onboard PSUs
used in digital circuits are in fact switchers. The only place where you can
still find linear regulators these days are in sensitive analog electronics.
I am a board designer myself, so I know what I am talking about. A typical
mobo will have a bunch of coils near the CPU. That's where you have a hefty
switching regulator generating CPU core voltage/voltages. If they used a
linear regulator they would have to waste half of the power since core
voltages are so low and the lowest voltage available from the big PSU is
3.3V.
Click to expand...

He said AGP slot, not CPU area. Many of the motherboards I own and have
seen still use a number of the 3 pin regulators on them.
If they used a
linear regulator they would have to waste half of the power since core
voltages are so low and the lowest voltage available from the big PSU is
3.3V.
Click to expand...

What's wrong is that statement - you don't "waste" anything, the
regulator doesn't "waste" anything from the PSU. You can easily drop the
+12VDC supply down to any lower voltage without "wasting" anything.
 
Leythos said:
He said AGP slot, not CPU area. Many of the motherboards I own and have
seen still use a number of the 3 pin regulators on them.
Click to expand...
Only for the +/-12v for the serial port.
What's wrong is that statement - you don't "waste" anything, the
regulator doesn't "waste" anything from the PSU. You can easily drop the
+12VDC supply down to any lower voltage without "wasting" anything.
Click to expand...
Do you understand how a linear regulator works?. If you generate a 1A 3.3v
supply from a 12v supply, using a linear regulator, you inherently have to
lose 8.8v at 1A as heat. 8.8W 'wasted'. A switching supply doing the same
job, will only typically lose perhaps half a watt. Given the current
required on the AGP supply rail (and processor supply rails) now, a system
based on linear regulators, would typically be putting over 200W out as
heat. No modern board can afford to do this, either in terms of the
temperature generated, or in terms of the actual source power available
from the supply. A common trick though is to use a 'composite' system,
with a switcher generating perhaps 5v, and then using an LDO linear
regulator from this. This is used in a few high quality boards. However
the '3 pin' devices you are seeing, are allmost certainly the switching
FETs, since the thermal limits of the TO220 package, make it unlikely to
be a linear regulator in this area.

Best Wishes
 
Do you understand how a linear regulator works?.
Click to expand...

Yea, I if I take the 7812, 7805, LM317, etc... regulator device, and
look in my Linear data book, it's the same as it's been since the 80's.
The device does not disapate heat or waste anything to provide the
specified power from the supply voltage.

I don't see it as disapating anything to provide the drop to the
requested level, I see it disapating heat to provide the X volts at y
MA, through the circuit. The drop doesn't generate the heat, the load on
the regulator does.
 
Yea, I if I take the 7812, 7805, LM317, etc... regulator device, and
look in my Linear data book, it's the same as it's been since the 80's.
The device does not disapate heat or waste anything to provide the
specified power from the supply voltage.

I don't see it as disapating anything to provide the drop to the
requested level, I see it disapating heat to provide the X volts at y
MA, through the circuit. The drop doesn't generate the heat, the load on
the regulator does.
Click to expand...

One thing to keep in mind, the OP said the cap was blown and in my
experience, if it was part of the switching power circuit, it would
almost certainly mean problems for his system.

Since he's not having any problems with it, then it must be OPEN and not
shorted and certainly not doing it's job. This leads me to believe that
it's just for filtering ripple on the board at some critical point that
requires flat voltage levels.

One last thing, if I setup a 7805 or LM317 regulator, and supply it with
12VDC and set the output to 5V, the heat generated under a 1A load is no
different than when I supply it with a 24VDC input.
 
It is the product of the current, and the voltage drop.
One thing to keep in mind, the OP said the cap was blown and in my
experience, if it was part of the switching power circuit, it would
almost certainly mean problems for his system.

Since he's not having any problems with it, then it must be OPEN and not
shorted and certainly not doing it's job. This leads me to believe that
it's just for filtering ripple on the board at some critical point that
requires flat voltage levels.

One last thing, if I setup a 7805 or LM317 regulator, and supply it with
12VDC and set the output to 5V, the heat generated under a 1A load is no
different than when I supply it with a 24VDC input.
Click to expand...
You really don't understand it do you. On a 1A load from a 12v input, a
7805, will have to dissipate 7W. From a 24v supply, it'll have to
dissipate 19W. The heat most definately _is_ different.
 
message |
| | > In article
| > (e-mail address removed) says...
| > > In article <[email protected]>,
| > > (e-mail address removed) says...
| > > > Do you understand how a linear regulator works?.
| > >
| > > Yea, I if I take the 7812, 7805, LM317, etc... regulator device,
and
| > > look in my Linear data book, it's the same as it's been since
the
| 80's.
| > > The device does not disapate heat or waste anything to provide
the
| > > specified power from the supply voltage.
| > >
| > > I don't see it as disapating anything to provide the drop to the
| > > requested level, I see it disapating heat to provide the X volts
at y
| > > MA, through the circuit. The drop doesn't generate the heat, the
load
| on
| > > the regulator does.
| It is the product of the current, and the voltage drop.
|
| > One thing to keep in mind, the OP said the cap was blown and in my
| > experience, if it was part of the switching power circuit, it
would
| > almost certainly mean problems for his system.
| >
| > Since he's not having any problems with it, then it must be OPEN
and not
| > shorted and certainly not doing it's job. This leads me to believe
that
| > it's just for filtering ripple on the board at some critical point
that
| > requires flat voltage levels.
| >
| > One last thing, if I setup a 7805 or LM317 regulator, and supply
it with
| > 12VDC and set the output to 5V, the heat generated under a 1A load
is no
| > different than when I supply it with a 24VDC input.
| You really don't understand it do you. On a 1A load from a 12v
input, a
| 7805, will have to dissipate 7W. From a 24v supply, it'll have to
| dissipate 19W. The heat most definately _is_ different.
|
|
|

Roger is correct, a switching PS circuit is far more "efficient" than
a traditional linear regulator circuit. Roger's explanation is
technically accurate in all respects. Since the cap in issue is near
the agp slot, I suspect it is not being used in a switching PS
circuit.

A review of a LM341/7805 datasheet
http://www.national.com/ds/LM/LM341.pdf reveals the following heat
dissipation formula:

PD = (VIN-VOUT) IL + VIN*IG

PD=Power Dissipation
VIN=input voltage
VOUT=output voltage
IL= load current driven into the "load"
VIN*IG=input voltage * Ig (regulator current usage)

It should be clear that the difference between Vin and Vout directly
and linearly impacts heat dissipation in the device.
 
It should be clear that the difference between Vin and Vout directly
and linearly impacts heat dissipation in the device.
Click to expand...

You would think so, and technically, I agree that I'm wrong, but in
practice it does not appear so. I have the same books, even the ones
from the 80's on those devices, and they say the same thing. What I see,
in the lab does not show what the book states.

And, yes, I clearly understand that a switching PSU is more efficient
that a linear one, that was never a question.

The question is that the OP posted that a cap had burst, that the
solution had leaked, and that he noticed no difference in operation.
While I am wrong on in power dissipation, I'm not wrong in the
reason/use of the caps on the board. The caps are used to filter the
ripple out of the supply source being used on the board. Since the cap
has not caused any noticeable difference, it's safe to assume that the
cap is Open and not shorted, that he could remove it without any change
in current operation, and that it most likely has nothing to do with a
switching power circuit on the board.
 
Caps can do many different things. It depends on the type and cicruit
design. If you want a 'hint' about the use of electrolytic caps on a
modern mobo, look carefully at the rating....if the ratiing is 105
centigrade you can be almost sure it's in a switching
circuit...why...well mobo producers try to get the board cost down to
the lowest possible level. 105 C caps cost significantly (in
production x 1000's of brds) but are needed in switching
(regulating/dropping) applications.

As for "why it kept working with an electrolytic cap that
'vented'...well, if you take a close look on most mobos, you'll see
that in order to get the bulk capacitance they need and still have a
low profile, most boards use multiple caps (add the UF value) in
parallel. Having 3 to 7 caps so connected is common....so; when one
such cap failed the mobo might still appear to be "just fine"...but
without an understand and the ability to measure the voltage, amperage
and ripple current etc under heavy loads...well, assuming "all is
still ok" is a risky guess.
 
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