N
new
I have a bad capacitor that is 6.3v 1500uf, will a 6.3v 2200uf work
instead.
Thanks
instead.
Thanks
M
MasterBlaster
According to these guys:
http://www.motherboardrepair.com/index.php?sec=faq
- I know one can replace a bad capacitor with another one, which is
- rated higher in voltage.
- I was wondering if this also holds true for farad rating...
- IE, a 1500uf cap went bad. Can it be replaced with a 2000uf cap?
-- A few problems can occur if the total capacitance of the filter circuit is changed.
-- 1) If total capacitance is too high, the turn-on surge current could be high
-- enough to trigger the OCP (over-current protection) in the ATX supply and
-- on the on-board regulators themselves.
-- 2) In this type of circuit, incorrect values can cause parasitic oscillation, which
-- will cause over-current, overheating and premature cap failure.
-- 3) Physical size limitations, 2200uf capacitors won't fit in the same area as
-- the 1500's!
D
Daniel Mandic
MasterBlaster said:
Maybe, it depends to the time. A 2200 would need longer to load, if it
is placed instead the 1500. But I don´t think that it will not work at
all. Maybe you have to restart the machine a second time, and then
.......
I have changed 4700 caps (somewhere in the AGP area). I have used two
caps, which were together approximately the same value as the orig.
small 4700 cap. 4700 I cannot get here to buy, and absolutely not in
such a small package as it was originally on the MB.
Well, it looks adventureous what I have soldered (two big cans)
Butit works. Everything isolated etc. etc...
Best Regards,
Daniel Mandic
P
Paul
http://www.motherboardrepair.com/index.php?sec=faq
http://www.motherboardrepair.com/index.php?sec=partinfo
For standard electrolytics, the volume occupied by the
cap should be the same from maker to maker. The manufacturing
process is pretty well the same for each of them (barring
accidents like using the wrong electrolyte formula
Ifyou find ones with a smaller overall volume (Ht*Pi*R*R), it
means somebody cheated.
There are some alternate types (Sanyo OSCON), but they
use quite different materials (solid electrolyte?), have
different pricing, and much better operating parameters.
Sometimes only one of those can replace four of the ordinary
ones. I don't recommend doing such a substitution yourself,
unless you understand all the issues. (Usually, people who
build these circuits, prototype them, and they never trust
all their equations unless proven in a lab prototype. For
hobbyist purposes, you might end up toasting your only
good processor...)
According to Gary on the web pages above, the 2200uF is a little
bigger. Which means, if the caps are shoulder to shoulder, they
may need to be bent outwards at an angle, so they can all fit.
That means leaving a little lead length on them. The switching
circuit operates at a minimum of a couple hundred KHz, and I
suppose a short length of leg on a couple of them won't hurt.
It adds inductance and a bit of resistance, degrading the ESR
and ESL (working out the magnitude of the effect should be
fun). Try to make sure the majority of capacitors are sitting
flush to the motherboard, like the originals.
You can learn a great deal about the board you are working on,
by reading the part number off the Vcore regulator chip, and
downloading the datasheet. For example, I've learned that the
capacitance value itself is not the most critical parameter.
In other words, the designer, when selecting the parts, wasn't
too worried about total capacitance. If the 1500uF went to
1200uF or 1000uF, the designer wouldn't have been too worried.
One parameter the designer might have worried about, is the
AC current rating through the cap. The purpose of capacitors,
is to shunt AC ripple through the cap, and into the ground
(that is the essence of filtering). Leaving the nice smooth
DC sitting there. The AC ripple is a voltage, the capacitor
presents an impedance (resistance in a sense), and an AC
current flows. In a large cap, this current is measured in
amps and is no joke. Each cap has a rating for how much
current it can take, as the AC ripple current makes the cap
warm up a bit. By putting a bunch of caps in parallel, the
designer is trying to handle all the current needed to divert
the ripple voltage.
As an example, someone was asking about a P2B-S motherboard
a few posts back. Here is the datasheet for the Vcore
regulator, with a nice section describing the capacitor
selection process:
******
http://www.intersil.com/data/FN/FN4/FN4567/FN4567.pdf
Output Capacitor Selection
An output capacitor is required to filter the output and
supply the load transient current. The filtering requirements
are a function of the switching frequency and the ripple
current. The load transient requirements are a function of
the slew rate (di/dt) and the magnitude of the transient load
current. These requirements are generally met with a mix
of capacitors and careful layout.
Modern microprocessors produce transient load rates above
1A/ns. High frequency capacitors initially supply the transient
and slow the current load rate seen by the bulk capacitors.
The bulk filter capacitor values are generally determined by
the ESR (Effective Series Resistance) and voltage rating
requirements rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the power pins of the load as physically possible.
Be careful not to add inductance in the circuit board wiring
that could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements. For example, Intel
recommends that the high frequency decoupling for the
Pentium Pro be composed of at least forty (40) 1µF
ceramic capacitors in the 1206 surface-mount package.
Use only specialized low-ESR capacitors intended for
switching-regulator applications for the bulk capacitors. The
bulk capacitor¹s ESR will determine the output ripple voltage
and the initial voltage drop after a high slew-rate transient.
An aluminum electrolytic capacitor¹s ESR value is related to
the case size with lower ESR available in larger case sizes.
However, the Equivalent Series Inductance (ESL) of these
capacitors increases with case size and can reduce the
usefulness of the capacitor to high slew-rate transient loading.
Unfortunately, ESL is not a specified parameter. Work with
your capacitor supplier and measure the capacitor¹s
impedance with frequency to select a suitable component. In
most cases, multiple electrolytic capacitors of small case size
perform better than a single large case capacitor.
******
Have a look at Gary's part suggestions
coding "1A" = 10 volts, "152" = 1500uF
647-UPW1A152MPH6 10 volt 1500uF (10mm x 25mm high part)
It is the 24th item down, right hand column, of page 2 -
0.045 ohms at 20C, 1440 mA ripple current rating.
http://www.nichicon.com/english/seihin/pdfs/e-pw.pdf
If you look at the tables, a 6.3V 2200uF is 10x25mm, and
is 0.045 ohms at 20C, 1440 mA ripple current. A 10V 1500uF
cap is also 10x25mm, and is 0.045 ohms at 20C, 1440 mA
ripple current. As long as the Vcore regulator design note
says that such small differences in capacitance are not
important, the other parameters are an exact match. (The
impedance is not broken out into an ESR and ESL component,
and that would be very educational information to have. It
would allow you to make a finer distinction between the
qualities of the caps.)
Gary's other suggestion was Panasonic EEU-FC1A152
The 1A152 being the same coding scheme as the example above.
http://www.panasonic.com/industrial/components/pdf/ABA0000CE22.pdf
Don't panic when you see the listing for 5000 hour life.
That is at 105C. The Arrhenius relationship (chemistry
reaction rate) applies here, and for every 7C drop in temp,
the lifetime doubles. At 60C, you are over 100000 hours.
http://www.panasonic.com/industrial/components/pdf/ABA0000PE26.pdf
I cannot find too much reference to determining ESL...
http://groups.google.ca/group/alt.e..._frm/thread/32839685d84ef401/badf56cb7c4c7784
http://www.chemi-con.com/u7002/applications.php
HTH,
Paul
N
new
Thanks for all the info from everyone. I found an old board and pulled
a 6.3v 1500uf to replace the bad 6.3v 1500uf
Here is the odd thing about physical size, the 6.3 2200uf size was
physically the same size exactly height circumference as the 6.3
2200uf. The one I pulled from an old board 6.3 1500uf was the same
size in circumference but about half the height but it did have the
same listing on it that I needed 6.3v 1500uf. Well I put in the right
one even though it was shorter and it seems to be working fine.
Thanks again for all your info and I did that all your advice and use
the correct Cap.