From: "Saved by Internet Explorer 11" Subject: SB-Projects: PC PSU Repair Tips Date: Thu, 26 Jun 2014 11:39:40 -0700 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01CF9133.513633A0" X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.17609 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01CF9133.513633A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.sbprojects.com/projects/pcpsu/index.php
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Very Important Warning!Warning! Read this =
first, even if=20
you are clever enough to remove all external power before you =
start to=20
open the PSU. Do NOT operate the PSU while it's = open! Not only can this cause a serious electrical shock, it can also = cause=20 short circuits, destroying the PSU for ever! Some basic knowledge about electronics and electronic = components is=20 mandatory when you intend to fix your PSU. PC PSU Repair TipsI know, PC Power Supply Units are very cheap. Why not =
chuck it=20
away when it's dead and put in a new one? Simple because the new =
one is=20
not always at hand. Or the PSU is a very special model, tailored =
to this=20
particular brand of computer. What's more, sometimes you can't =
even get a=20
separate PSU without buying an entire PC case to go with it. So =
you'd have=20
to throw away at least one of them, which is of course a shame. =
This description is by no means intended to solve all your = power supply=20 problems. I only cover a few basic tips so you'll know where to = look. If=20 the golden tip is not among them, bad luck, throw it away and buy = yourself=20 a new one. Please don't ask me for more tips, because these are = all I can=20 give you. One important tip in advance: "Never try to operate the PSU = without a=20 load". Most switching mode power supplies expect some load on the=20 regulated output (usually the +5 V on a computer PSU). If you = intend to=20 try out the PSU without a computer you can always connect a 12 V = car light=20 bulb to the +5 V output as artificial load. Is the main fuse alive?This is a good point to start looking for the problem. If the =
main fuse=20
is dead, check the main switching component for shorts. Usually =
the main=20
switching component is a transistor or a FET and can be found on =
one of=20
the heat sinks on the primary side of the PSU. If it's shorted =
you're in=20
bad luck. It is very likely that the transistor killed part of the =
control=20
circuit as well. The main fuse is still alive!That's more like it! There's a big chance that we can = fix it. Well, there are a few possible causes why the PSU doesn't work = anymore:=20
There are probably dozens of other causes why a PSU has died. =
Don't=20
spend too much time and effort to find it if these tips don't =
solve your=20
problem though, considering the current prices of new ones. The Start ResistorIt is quite obvious that a PSU supplies some low voltages on =
its=20
secondary side. But it also generates at least one voltage on the =
primary=20
side as well because the control circuit would like to have =
something to=20
eat too. Usually this voltage is simply derived from an extra coil =
around=20
the main switching transformer. One popular way to solve this problem is the use of a =
start=20
resistor. This is a relatively high ohmic resistor (usually in the =
range=20
between 390 kΩ to 680=20
kΩ) which is placed between the 300 V=20
DC primary voltage and the control circuit's power supply. =
Remember that most ATX power supplies are never = really switched=20 off. Normally they remain in standby when the computer is not in = use. Therefore such a PSU can run forever, even with a dead start = resistor. Only when you have removed the power completely you will find = that the=20 computer won't start up any more. This is a clear indication that = the=20 start resistor has died. The start resistor is usually a normal =BD W=20
or =BE W carbon resistor and is =
always connected=20
to the +300 V line on the primary =
side of the=20
PSU. |