AIM: INTRODUCTION TO COMPUTER HARDWARES
TIME-80 Mins( 02 Pds)
STEPS:(a) Introduction to computer power supply and its type.
(b) Form factor type with their own supply variety.
(c) Connectors attached with power supply.
TIME-10 MIN
TIME-35 MIN
TIME-35 MIN
(a) Introduction to computer power supply and its type.
TIME-10 MIN
Power supply
PC
power
supply
unit
(PSU) is the
device
that
converts
the
input
AC
voltage to the
DC
voltages
needed by the
personal
computer.
Since
the
introduction of
IBM
PC/XT
there
have
been about a
dozen
of
different
PC
standards
(such as AT,
Baby AT, LPX,
ATX, SFX, PS3, WTX, TFX, LFX, CFX, EPS) that differ by their form factors, connectors
and voltage/current ratings. Output rating of a typical modern DC power supply for a
personal computer is ranging anywhere from 240 W to kilowatt. PSU over 600W are used
mainly for Extreme Gaming & Media Entertainment PC, SLI support, servers or industrial
PCs.
Today's typical desktop PC PSU produces the following DC outputs: +5V, +3.3V,
+12V1, +12V2, -12V and standby 5V. Additional "point of load" DC-DC converters
step down 12V to the CPU core voltage and other low voltages needed for
motherboard components.
To support 75 watt PCI Express requirements in the current systems the 2 x 10 main power
connector has been replaced by a 2 x 12 connector. The 2 x 2 power connector is added
for the second 12V rail that supports the processor.
Power supplies for computers utilize switching mode technology. Most of today's
models are ENERGY STAR® compliant, which basically means they consume <10%
of rated power in standby mode. However the efficiency of a typical cheap desktop
PSU in active mode used to be 65-70%. Recently introduced an electric utility-funded
incentive program called 80 PLUS® requires computer and server power supplies to
demonstrate efficiency >80% at 20% to 100% of rated load and Power Factor >0.9 at
rated load. The updated ENERGY STAR Computer Specification (Version 4.0) also
requires
the
above
efficiency
levels
for
internal
PSU.
b) Form factor type with their own supply variety Time-35 Min.
The form factor of the power supply refers to its general shape and dimensions. The form
factor of the power supply must match that of the case that it is supposed to go into, and the
motherboard it is to power. You may not find too many people discussing form factors as they
relate to power supplies--this is because power supplies normally come included in system
cases, so people talk about the form factor of the case instead. This is changing as the power
supply starts to get more of the attention it really deserves. Also, newer power supply form
factors can often work with more than one type of case, and vice-versa
The ATX specification was created some years ago at a time when desktop CPUs
generated no more than ~30W. Now, they are up over 130W. The airflow arrangement of
exhausting hot case air out through the PSU no longer makes as much sense as it did in
the past. The PSU has to handle both its own self-generated heat, which is naturally higher
than before, as well as the heat generated by the other components.
Fast-spinning fans make a lot of noise, especially when confined in a small space with
nearby airflow obstructions. It is not unusual for the noise of a PSU to be 12-15 dB higher
than the rated noise of its fan in free air. The noise is further increased by the way a PSU is
mounted in a typical tower case: the typical 2-2.5 Kg weight "hangs" off the top of the back
panel on 4 screws. In this mounting configuration, excitation of case panel resonances by
direct transfer of PSU fan vibrations is almost unavoidable. The end result is more noise,
especially as a droning type of hum in the lower frequencies.
The quietest PSUs if you want to jump straight there) feature either no fan at all or a fan
that spins at low speed under most conditions. Keep in mind that components will tend to
run a bit hotter than usual as a result of reduced airflow. This can be a concern if the normal
ambient room temperature is high or if very hot components are used. The best fancooled models have low normal fan speed, and allow the fan to ramp up to full speed
only when really necessary.
There are many different motherboard/case form factors, such as Mini-ATX, LTX, FlexATX, AT, Mini-ITX, etc. There are also many proprietary cases that don't conform to any
general form factor. ATX power supplies can often be used, but some cases require
different PSU form factors, such as STX for Flex-ATX cases. In time, we will expand our list
to include different form factor PSUs.
In summary:
The first PC was of course the IBM PC. Its power supply, and that of its hard-driveequipped successor, the IBM PC/XT, used the same original form factor. These
systems were all desktop units, with the power supply tucked into the rear of the case
on the right-hand side, and controlled via an up/down toggle switch. While the PC/XT
power supply began as an IBM design, IBM's key decision to keep the PC
architecture open allowed "clone" manufacturers to make similar PC boxes and use
the same size and shape of power supply for interoperability. In this manner, the first
PC form factor "standard" was born.
The Baby AT form factor is so named because it is a smaller version of the original AT
form factor.
It has the same height and depth, but is about 2" narrower. Since it is "similar but smaller",
the Baby AT power supply will fit both in Baby AT form factor cases and in full-size AT
cases as well, in both tower and desktop styles.
It has the same output motherboard and drive connectors as the AT. Due to this flexibility,
and the fact that it was introduced at around the time that PCs began to really grow in
popularity, the Baby AT form factor reigned as the most popular design for over a decade-far longer than any other. From around 1985 to 1995
This form factor has now been replaced in new systems by the ATX and other form factors.
However, the huge installed base has given Baby AT momentum and given manufacturers
of new components incentive to provide upgrade options for the millions who still use these
systems.
ATX (NLX) Form Factor
The ATX power supply design differs from the previous market standards, the Baby
AT and LPX form factors, in several important ways:
True Standard: The ATX form factor is a standard, as opposed to the "de facto standards"
of prior form factors.
+3.3 V Power: ATX systems were the first to include +3.3 V power directly, avoiding the
need for voltage regulators to provide it on the motherboard.
Soft Power: ATX systems were the ones where the +5 Standby and Power On signals
were introduced. These signals are used along with a change to the way the power switch
works, as part of the "Soft Power" feature that enables features such as allowing the
operating system to turn off the PC.
Changed Motherboard Connectors: Breaking with 15 years of tradition created by the
PC/XT, AT, Baby AT and LPX form factors, Intel specified new motherboard connectors for
the ATX form factor. This was in part due to the additional signals used by the ATX power
supply and motherboards. For compatibility, some motherboards include both the new and
old style of connector.
Modified Fan Direction and Placement: One of the goals of the original ATX specification
was to change the way the power supply fan worked. At around the time ATX was introduced,
cooling fans were becoming the standard for the newer, faster CPUs on the market. Instead of
exhausting air out the back of the case as had always been the norm, Intel wanted to use this
exhaust air to cool the processor directly, saving the cost of a cooling fan. Therefore, the ATX
specification calls for the fan to run in the opposite direction and be placed near the CPU's
location on the motherboard, to blow on it for cooling. The other advantage of this method is
that it keeps the system cleaner, since air entering the case all comes from one place, and can
be
filtered
if
necessary.
Unfortunately, while a good idea, this hasn't worked out quite the way Intel hoped. The primary
problem is that newer CPUs continue to generate more and more heat as they get faster, and
a regular power supply fan doesn't have enough flow to cool them properly. This problem is
compounded by the fact that the air blowing on the CPU is warmed by the components in the
power supply itself, so it is several degrees above ambient temperature before it ever gets near
the CPU. Thus, newer versions of the ATX specification make the fan direction optional. The
newest ATX power supplies have gone back to the old style of placing the fan on the back of
the power supply and exhausting air to the outside.
SFX Form Factor
è As part of the continuing trend towards smaller and smaller PCs, Intel in 1997 introduced
the new microATX form factor, based upon the original ATX form factor.
è In 1999, Intel produced the FlexATX addendum to the microATX specification, detailing
plans for an even smaller motherboard and case standard. Neither of these form factors
include specifications for a power supply. Instead, Intel created the SFX power supply form
factor, which they may optionally use. The "S" in "SFX" is for "small" of course! microATX
and FlexATX systems can also use the ATX power supply, though since miniaturization is
the key with these systems, the SFX power supply makes much more sense.
WTX Form Factor
If the SFX form factor is the little brother to ATX, WTX isn't quite its big brother. WTX is
more like its overgrown third cousin from a distant country. :^) Introduced by Intel (who else)
in 1998, and revised in 1999, the WTX form factor is designed specifically for workstations
(thus the "W" in "WTX"). WTX defines a standard for motherboards, cases, and power
supplies.
To meet the increased needs of the largest regular PC systems, the WTX form factor is
totally different from the other PC form factors. It is designed in a modular way from the
ground up to allow it to meet the needs of large, multiple-CPU systems now and in the
future. The system is segmented physically into different "zones" where different functions
are supposed to be incorporated into the system. The motherboard is mounted on a special
mounting plate which gives motherboard makers the flexibility to design boards without
"hard-coded" mounting hole restrictions.
Unsurprisingly, WTX power supplies are large and powerful. The WTX specification actually
includes design guides for three specific sizes of power supply: 460 W, 610 W, and a
whopping 800 W, though manufacturers are not limited to those particular numbers. For
designs up to about 500 W, a single power supply fan is specified, with overall power
supply dimensions of 150 mm width x 230 mm depth x 86 mm height. For larger capacity
supplies, a dual-fan configuration is recommended, which increases the width of the
package to 224 mm.
===============================================
===============================================
===============================================
©Connectors attached with power supply
Time-35 Min
PC Main power connector (usually called P1): Is the connector that goes to the motherboard to
provide it with power.
The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire mentioned
above (it is usually green). This connector is the largest of all the connectors.
In older AT power supplies, this connector was split in two: P8 and P9.
If you have a power supply with 24-pin connector, you can plug it into a
motherboard with a 20-pin connector.
In cases where the motherboard has a 24-pin connector, some power supplies
come with two connectors (one with 20-pin and other with 4-pin) which can be used
together to form the 24-pin connector
24-pin ATX power supply connector
(20-pin omits the last 4: 11, 12, 23 and 24)
Color
Signal
Pin
Pin
Signal
+3.3 V
1
13
+3.3 V sense
+3.3 V
2
14
-12 V
Ground
3
15
Ground
+5 V
4
16
Power on
Ground
5
17
Ground
+5 V
6
18
Ground
Ground
7
19
Ground
Power good
8
20
-5 V
+5 V standby
9
21
+5 V
+12 V
10
22
+5 V
+12 V
11
23
+5 V
+3.3 V
12
24
Ground
Color
4-Pin Peripheral power connectors
usually called Molex for its manufacturer\
These are the other, smaller connectors that go to the various disk drives of the computer.
Most of them have four wires: two black, one red, and one yellow.
Unlike the standard mains electrical wire color-coding, each black wire is a ground, the
orange wire is +3.3 V, the red wire is +5 V, and the yellow wire is +12 V.
4-Pin Floppy drive power connectors (usually called Mini-connector):
This is one of the smallest connectors that supplies the floppy drive with power.
In some cases, it can be used as an auxiliary connector for AGP video cards.
Its cable configuration is similar to the Peripheral connector.
Auxiliary power connectors: There are several types of auxiliary connectors
designed to provide additional power if it is needed.
Aux connectors
Serial ATA power connectors: a 15-pin connector for components which use
SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and
+12 volts.
Most modern computer power supplies include 6-pin connectors which are generally used
for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on
the latest model power supplies. Each PCI Express 6-pin connector can output a maximum
of 75 W.
A C14 IEC connector with an appropriate C13 cord is used to attach the power supply to
the local power grid.
Troubleshooting PC power supplies
TIME- 80 MIN ( 2 Pds )
Isolating PC power supply problems can be either very straightforward or extremely difficult,
depending largely on the type of problem, the symptoms that you observe, and when the
symptoms occur. Although a completely dead PC is almost always due to a faulty supply,.
Since every device or component attached to your PC depends either directly or indirectly on the
power from the system’s supply, developing a methodology for isolating power problems can be
quite
useful.
Simply replacing a power supply is common practice when a supply problem is suspected.
Although this can be a very effective troubleshooting method (especially for dead systems), there
may be situations where doing so is just not an immediate option. For example, if you are working
in the field or a system uses a proprietary supply, you may not have a proper replacement readily
available. In some situations, it may be ineffective and inconvenient to replace a supply as a first
option. Even if you do have a replacement available, you may find that the power supply is not the
source of the problem. So to save time, you should do some simple troubleshooting first.
Unlike AT supplies, ATX supplies are connected to a PC’s motherboard at a main 20-pin
connector. The newer ATX 12V supplies have an additional 4-pin +12V connector, and the ATX
standard also allows for an auxiliary and optional connector. For this article, however, I am only
concerned with the main 20-pin connector whose pin-out is shown in Figure A. The color at each
pin represents the color of the wire on the supply cable that will be connected to the pin. Most, but
not all, ATX supplies use this color scheme. Notice that ATX supplies use five different voltage
rails of which the +3.3V, +5V, and +12V are the most important. The GND pins are at common
ground potential that on PCs, like on most other electronic devices, is also the potential of the
system chassis.
Figure A:
This shows the ATX main 20-pin connector and color scheme. The key keeps the
supply cable from being connected backwards.
When you plug in an ATX supply—and the rocker switch on the supply, if there is one, is
on—there will always be a nominal +5V at the 5VSB pin (pin 9) regardless of whether the
computer is turned on or not. This standby voltage is used to power the push-button
circuitry that actually turns on the machine. It is also used in conjunction with the PS_ON
pin (pin 14) to allow software such as the operating system to control the power to the
system. Normally, the PS_ON pin will be at a nominal +5V when the system is off. When
you press the case switch to power on the system, the voltage at the PS_ON pin will drop
to ground potential (0V), and the ATX supply will be powered on. A short time (a few
hundred milliseconds) later, the power supply will send a Power OK signal to the
motherboard via the POWER_OK pin (pin 8), and the system will start its boot procedure.
Proprietary power supplies may not use the standard 20-pin ATX connector. However, these
power supplies will still provide the ATX voltages and signals albeit in a different configuration.
You should still be able to troubleshoot these supplies in a similar fashion as standard ATX
supplies.
The following troubleshooting tools you require to have on hand.
Multimeter
The multimeter is the single most important troubleshooting tool for an electronics technician.
Multimeters come in two flavors: analog and digital (DMM). Both types serve the same purpose,
but I will concentrate on DMMs since they are easier to read and use. Figure B shows a DMM.
Figure B
Here, a DMM measures an AC line voltage.
An ATX power supply tester that you can procure or
can easily be fabricated .
This very simple device (Figure C) consists of two power resistors connected to +5V and GND
through an ATX 20-pin connector. An LED is provided to show POWER_OK, and a jumper wire
drives PS_ON low so that the supply can turn on.
Figure C
An ATX power supply tester is a simple device.
Procedure
To use an ATX power tester, you first unplug the power cord at the PC end. Then, you disconnect
all devices from the power supply including drive bay devices, motherboard, and any fans that are
directly attached to a power supply connector. Next, attach the power supply’s main connector to
the tester’s 20-pin connector. Reconnect the power cord to your PC and check to see if the
tester’s LED lights up and that the fan is working. If the LED does not light up, you can be quite
certain that your supply is bad. If it does light up, you can be reasonably sure that it’s good.
However, as Figure E shows, these testers are not extremely thorough so use them as a general
test only. Remember to unplug the cord before removing the tester.
Figure-E
Many times, a power supply will not fail immediately but will instead fail gradually. Before complete
supply failure actually occurs, the system may lose power during operation and then power up
again only after an extended period. Eventually, you may be able to turn on the power supply (i.e.,
the fans spin and the power LED lights up), but there will be nothing on the display and no BIOS
boot activity. You can treat this situation in the same manner as a dead system problem and
troubleshoot it accordingly.The same power supply tested in the image above has had its +12V
line (yellow wire) cut. The ATX tester is still indicating a good supply because it only checks for
Power OK by loading the +5V rail. Use the ATX tester as a general test only.
If you are using a multimeter instead, set it to measure DC voltage and connect the black
probe to any convenient place on the chassis. Reconnect the power cord. Before proceeding,
Determine whether or not the ATX supply is actually turning on when the system power
switch is pressed. Do this by first placing the red probe on the PS_ON pin (14) that usually
has a green wire attached. This should give you a reading of about +5V on your meter. After
pressing the power button, the signal should swing close to 0V (a few millivolts), indicating that the
supply has been switched on.
Next, determine whether the supply is providing stable power to the system. To do this,
move the red probe to the Power OK or Power Good pin (8) that usually has a gray wire
connected. Your meter should show approximately 5V, but a reading between 3 to 6 volts is
acceptable. If this value is close to 0V or out of range, your supply is probably bad. Replacing the
supply at this point will often fix the problem.
Keep in mind that the 20-pin connector from the supply must remain connected to the
motherboard in order for the supply to turn on and provide a POWER_OK signal. If the system
does not turn on after all internal devices directly connected to the supply have been checked, you
can then unplug the system, remove all adapter cards from the motherboard, reconnect the cord,
and test for power. If the PC still does not turn on, the most practical option left is replacing the
supply.
If the system you are troubleshooting is suffering from random lockups and reboots, it could be
that the power supply is to blame. Unfortunately, there are many other culprits that can cause the
same type of symptoms. Lockups and sporadic reboots may also be related to software,
hardware, power supply problems, external power problems, system configuration, etc.
Some power supply problems that may cause boot, lockup, and stability problems include:
Overloaded power supplies—
Dirty power or poor regulation.Malfunctioning supply fans.Malfunctioning internal supply components.Supplies with poor Power Good timing.You can begin isolating a power supply as a source of lockup and stability problems by examining
the most common causes of these problems. Use a DMM, BIOS sensor info, or a program like
Motherboard Monitor to determine how close output voltages are to nominal (Figure F).
Voltages that deviate greatly from nominal (especially at lower voltages) can indicate supply
problems.
Figure F
Motherboard Monitor can display a variety of motherboard sensor data and can be set
to trigger an alarm or send notification if a value is not within the limits you specify.
Notice that in the image above, all the voltages shown are within one percent of their nominal
values. This indicates that the supply is providing excellent regulation and should be working well.
Determine if your power supply’s output power specifications are adequate to support all of your
system’s components.
If your system tends to lock up during bootup, you may be overloading the +12V rail.
To continue isolating the supply, try to eliminate as many other sources of lockups and stability
problems as possible. Some of the most common include:
i)
Bad or incorrectly configured RAM.
ii)
Heat-related problems. (Check your fans and airflow.)
iii)
Hardware conflicts. (Even on PCI, some devices do not like to share IRQs.)
iv)
Software conflicts. (Keep your firmware and drivers up to date.)
v)
Corrupt system or program files
vi)
Noisy and dirty outlet power. (Make sure the power received by the PC is clean, properly
grounded, and contains no ground loops.)
These are the most common causes of system lockups and reboots but are by no means the only
possibilities. After you have exhausted your options, try replacing your supply with a high-quality
unit. Remember that cheap power supplies that operate very closely to or at their specified
maximum
ratings
are
the
cause
of
many
problems.
Conclusion
Replacing a suspect power supply can be a quick and effective solution. However, it can also be a
hit or miss proposition that can result in wasted time. To ensure thoroughness and as a
requirement for some types of problems, you should try to isolate a power supply as the source of
a problem. This is not always easy and can require a considerable amount of patience before the
actual problem is found, but by recognizing symptoms, analyzing operating information, and
understanding system requirements, you will be able to establish system stability.