Replacing caps on any PSU

[laser]

This tutorial I will write for fun ...designed to cover any cap replacement of any computer power supply..for advanced users..I hope will be useful

OK

When you dismantle any computer ' Power supply you will found lots of caps inside..small and bigs

here is the list of caps you will found


* 2 big caps 200v rated between 220uf and 630uf (never fail)

* small caps (never fail)

*the problematic high capacitance caps: you will found between 5 and 8



these high capacitance caps are there to ripple all voltages of the ATX or AT Power supply

there one for each voltage...5v 12v -12v 5vsb 3.3v -5v
*but sometimes on the 5v line there are 2 or 3 in parallel to ripple the most problematic line

how many capacitance is commonly used:

on the 5v line: between 2200uf and 4700 uf
on the 12v line: between 1000uf and 2200uf
on the 3.3v line:between 1000uf and 2200uf
on the -12v line: between 470uf and 1000 uf
on the +5vsb line: 1000 uf
on the -5v line: between 470uf and 1000 uf


*The 5v line

This is the most problematic line:it power ups the vcore of the cpu, the ps2 and usb ports and powerups lot of things.....very often you will found bulged caps there,if not bulged...they can be wasted and can offer low capacitance (check always the caps on this line) cause is the line of undesirable crashes and errors and it can fry your motherboard if there are not good capacitance there

*The 12v line

this is the second most problematic line...it power up hardisks,dvd and cdroms
If you have lot of this things...the cap of this line can be very stressed
(check always the caps on this line)

*The -12v line

This is the third most problematic line....used only for the motherboard...sometimes you will found a bulged cap..but it not causes mayor problems

*the 3.3v line

this line will power up ram modules......it's very rare found bulged caps or wasted caps there....unless you overclock the computer and you raise the memory voltage

*+5vsb

this line is always ON even if the computer is off....never used and never stressed unless you select with a jumper on the motherboard power up PS2 and USB ports...(I don't recommend that)
also this line power up some things in the bios


I will continue later

[Toasty]

Re: Replacing caps on any PSU

...* 2 big caps 200v rated between 220uf and 630uf (never fail)
* small caps (never fail)...

Working in electronics for 35+ years has taught me to NEVER say never.

Example:
Antec SL350 - 2 - 820uF/200v not bulged or leaking, both reading below 500uf. Just a bit outside the +/- 20% I think...

Same supply, 100uF/10v (5mm cap) very high uA leakage reading and 39uF capacitance.

USUALLY is a safer word. Sometimes. Perhaps.



Toast

[Toasty]

Re: Replacing caps on any PSU

Timed out on post edit. Another thought...

When you dismantle any computer ' Power supply you will found lots of caps inside..small and bigs...

Lots? Not necessarily true, especially on the newer PSU's. Easily 30% to 50% less of the number of caps there used to be.

Cheers!


Toast

[Krankshaft]

Re: Replacing caps on any PSU

here is the list of caps you will found

* 2 big caps 200v rated between 220uf and 630uf (never fail)

If the PSU you are repairing has Active PFC there will only be one filter cap.

[kc8adu]

Re: Replacing caps on any PSU

wrong on the small caps never going bad.
ask the owner of any bestec power supply who lost their motherboard when that 10@50 went open.

[Oklahoma Wolf]

Re: Replacing caps on any PSU

If the PSU you are repairing has Active PFC there will only be one filter cap.

Not always. I reviewed a Silverstone fanless unit that had four of them in parallel. I have another one here with three in parallel. Some of the big kilowatt class units use two in parallel as well because one would be too big.

AcBel as an OEM seems to use two in series a lot as well.

And yeah, the little ones can go bad. So can the main filters.

[Harvey]

Re: Replacing caps on any PSU

Its worth remembering that for the last 5 years or so ATX PSUs don't have the -5V rail anymore. Often the cable harness has the correct wire - its just not connected internally (and sometimes the PCB has the holes for the components).

[laser]

Re: Replacing caps on any PSU

Working in electronics for 35+ years has taught me to NEVER say never.

Example:
Antec SL350 - 2 - 820uF/200v not bulged or leaking, both reading below 500uf. Just a bit outside the +/- 20% I think...

Same supply, 100uF/10v (5mm cap) very high uA leakage reading and 39uF capacitance.

USUALLY is a safer word. Sometimes. Perhaps.



Toast

thanks for reading

I replaced "never fail" with "almost never fail"
I hope you will be satisfied

of course,by the time all caps lost capacitance....but almost never you will found problems with low capacitance capacitors..... unless they were manufactured by Fuhjyyu which I consider the most undesirables caps on the market

[laser]

Re: Replacing caps on any PSU

Its worth remembering that for the last 5 years or so ATX PSUs don't have the -5V rail anymore. Often the cable harness has the correct wire - its just not connected internally (and sometimes the PCB has the holes for the components).

you are right

some PSUs lacks the -5v line....even some new PSUs have the line but lacks a capacitor to ripple that line ...if not ... there are a small one (around 100uf)





btw,

thanks guys for reading..I will continue later ..I hope you like it and you found useful

[hkivan]

Re: Replacing caps on any PSU

If the PSU you are repairing has Active PFC there will only be one filter cap.

my Delta 400W active PFC PSU has 2 680uF 200V rubycon on the primary
side .

[Per Hansson]

Re: Replacing caps on any PSU

A little note on the voltage rails
On old computers 5v was used for the CPU

But this very long ago (about year 2000 or so) got changed into the +12v rail

Sometimes manufacturers use 5v or 12v for memory
And most oftenly (from personal experience) the cap for the +5v standby will be the first cap to fail, hail Antec! (which is very dangerous because it causes the Southbridge on the mainboard to burn out if the voltage drifts too high)

[KeriJane]

Re: Replacing caps on any PSU

my Delta 400W active PFC PSU has 2 680uF 200V rubycon on the primary
side .

My Delta 980W has Active PFC and Three 270uf/450v NCC KMD on the Primary.
Oh! it's a proprietary Mac Pro PSU with Six 12v rails and One 5v Standby.

Have Fun,
Keri

Wondering what all those 3.3v wires are for in an ATX PSU....

[Wizard]

Re: Replacing caps on any PSU

by 1995 it used to be heavy on 5V (20A typically) and 12V (8A) especially when a machine DID have 2 or 3 5.25" hard drives even full height HD. That's with 200W to 250 ish PSU. How efficient.

Cheers, Wizard

[999999999]

Re: Replacing caps on any PSU

A little note on the voltage rails
On old computers 5v was used for the CPU

But this very long ago (about year 2000 or so) got changed into the +12v rail

Sometimes manufacturers use 5v or 12v for memory
And most oftenly (from personal experience) the cap for the +5v standby will be the first cap to fail, hail Antec! (which is very dangerous because it causes the Southbridge on the mainboard to burn out if the voltage drifts too high)

Some Intel systems were, but the timing is subject to question, for example Asus A7N8X, a very popular board came out shortly before 2003 then thru 2004 used 5V rail for CPU VRM, and video cards at that time (roughly FX5900/Radeon 9700) were also still using more 5V rail derived power than today.