Simple Siwtch Mode Power Supple Repair tips (single UC3843 chip)
If it needs a load to start up it
would have to provide at least some power to detect whether a load was there or
not! PSUs that need a load will generally start and stop cyclically, making a
distinctive ticking noise.
In my experience, most SMPS that have primary supply but no output are lacking the 'kick start' power. I can't tell you which components provide it without seeing a schematic but most SMPS provide the working voltage for the UC3843 from the transformer itself, of course, when you first switch on there is no power to the regulator from the transformer so it can't work. They use an alternative 'weak' power source to get the circuit working, then the main source from the transformer takes over. The usual problem is the 'weak' power source is missing so it never has chance to start running.
Some SMPS use a capacitor to provide the initial power, it would be connected between the high voltage line and the regulator so it's charge current flows through the regulator and lifts it's supply up for a moment. If your power supply uses that method, look for low value (typically < 10uF) electrolytic capacitor that has a high working voltage, usually > 200V rated. There are likely to be other components in series with it, most likely a resistor to limit the surge current and maybe a diode to make sure it discharges quickly when the power is turned off.
Sometimes, but rarely, there will be a high power resistor > 2W between the high voltage and the regulator. It's less common because they run constantly hot and are more expensive than a small capacitor.
I would say 90% of the time the problem is the low value capacitor.
In my experience, most SMPS that have primary supply but no output are lacking the 'kick start' power. I can't tell you which components provide it without seeing a schematic but most SMPS provide the working voltage for the UC3843 from the transformer itself, of course, when you first switch on there is no power to the regulator from the transformer so it can't work. They use an alternative 'weak' power source to get the circuit working, then the main source from the transformer takes over. The usual problem is the 'weak' power source is missing so it never has chance to start running.
Some SMPS use a capacitor to provide the initial power, it would be connected between the high voltage line and the regulator so it's charge current flows through the regulator and lifts it's supply up for a moment. If your power supply uses that method, look for low value (typically < 10uF) electrolytic capacitor that has a high working voltage, usually > 200V rated. There are likely to be other components in series with it, most likely a resistor to limit the surge current and maybe a diode to make sure it discharges quickly when the power is turned off.
Sometimes, but rarely, there will be a high power resistor > 2W between the high voltage and the regulator. It's less common because they run constantly hot and are more expensive than a small capacitor.
I would say 90% of the time the problem is the low value capacitor.
ATX
Power supply repair
I need for my tests some good
quality power supply. I have 12v 2amp, 3amp etc. and few boost converters.
I recently found my old ATX power supply , Odeyssey 400watt ATX power supply (dated OCT 2005).
I thought may be if I could repair it without much effort it is worth keeping as an additional power supply. ( I have plans to take 5-8 amps if possible to charge my SLA battery).
(images are attached below)
it is one with 2 x 13007 at the primary and one more (5vsb) installed on the same heat sink.
I took out the STD 13007 and checked it, seems okay. but I have an additional 13007 which when checked I saw DVM reading between Collector and emitter ( like what we get with TIP122 -Epitaxial Darlington). is it normal?
The third one in the row I think is burned (see pic) , I cant read the no on it. when tried with dvm , diode mode - no reading at all.
I tried online to find part and found this page
http://www.overclock.net/t/769505/li...t-it-could-fly
the package and name is different but the inside is atleast 90% the same. it has a mention of C2057S transistor for 5Vsb. I searched online and found nothing. is it 2SC2057 ? I cant find that too. any idea about a possible replacement?
I recently found my old ATX power supply , Odeyssey 400watt ATX power supply (dated OCT 2005).
I thought may be if I could repair it without much effort it is worth keeping as an additional power supply. ( I have plans to take 5-8 amps if possible to charge my SLA battery).
(images are attached below)
it is one with 2 x 13007 at the primary and one more (5vsb) installed on the same heat sink.
I took out the STD 13007 and checked it, seems okay. but I have an additional 13007 which when checked I saw DVM reading between Collector and emitter ( like what we get with TIP122 -Epitaxial Darlington). is it normal?
The third one in the row I think is burned (see pic) , I cant read the no on it. when tried with dvm , diode mode - no reading at all.
I tried online to find part and found this page
http://www.overclock.net/t/769505/li...t-it-could-fly
the package and name is different but the inside is atleast 90% the same. it has a mention of C2057S transistor for 5Vsb. I searched online and found nothing. is it 2SC2057 ? I cant find that too. any idea about a possible replacement?
200W ATX PC POWER SUPPLY
Introduction
Here I bring you wiring diagram of PCs power supply of DTK
company. This power supply has ATX design and 200W performance. I was drawed
diagram, when I repaired this power supply.
Schematics diagram
Circuit description
This power supply circuit uses chip TL494. Similar circuit
is used in the most power supplies with output power about 200W. Device use
push-pull transistor circuit with regulation of output voltage.
Input part a standby supply
Line voltage goes through input filter circuit (C1, R1, T1,
C4, T5) to the bridge rectifier. When voltage is switched from 230V to 115V,
then rectifier works like a doubler. Varistors Z1 and Z2 have overvoltage
protect function on the line input. Thermistor NTCR1 limits input current until
capacitors C5 and C6 are charged. R2 and R3 are only for discharge capacitors
after disconnecting power supply. When power supply is connected to the line
voltage, then at first are charged capacitors C5 and C6 together for about
300V. Then take a run secondary power supply controlled by transistor Q12 and
on his output will be voltage. Behind the voltage regulator IC3 will be voltage
5V, which goes in to the motherboard and it is necessary for turn-on logic and
for "Wake on something" functions. Next unstabilized voltage goes
through diode D30 to the main control chip IC1 and control transistors Q3 and
Q4. When main power supply is running, then this voltage goes from +12V output
through diode D.
Stand-By mode
In stand-by mode is main power supply blocked by positive
voltage on the PS-ON pin through resistor R23 from secondary power supply.
Because of this voltage is opened transistor Q10, which opens Q1, which applies
reference voltage +5V from pin 14 IO1 to pin 4 IO1. Switched circuit is totally
blocked. Tranzistors Q3 and Q4 are both opened and short-circuit winding of
auxiliary transformer T2. Due to short-circuit is no voltage on the power
circuit. By voltage on pin 4 we can drive maximum pulse-width on the IO1
output. Zero voltage means the highest pulse-width. +5V means that pulse
disappear.
Start of supply
Somebody pushes the power button on computer. Motherboard
logic put to ground input pin PS-ON. Transistor Q10 closes and next Q1 closes.
Capacitor C15 begins his charging through R15 and on the pin 4 IC1 begins
decrease voltage to zero thanks to R17. Due to this voltage is maximum
pulse-width continuosly increased and main power supply smoothly goes run.
Normal operation
In a normal operation is power supply controlled by IC1.
When transistors Q1 and Q2 are closed, then Q3 and Q4 are opened. When we want
to open one from power transistors (Q1, Q2), then we have to close his exciting
transistor (Q3, Q4). Current goes via R46 and D14 and one winding T2. This
current excite voltage on base of power transistor and due to positive feedback
transistor goes quickly to saturation. When the impulse is finished, then both
exciting transistors goes to open. Positive feedback dissapears and overshoot
on the exciting winding quickly closes power transistor. After it is process
repetead with second transistor. Transistors Q1 and Q2 alternately connects one
end of primary winding to positive or negative voltage. Power branch goes from
emitor of Q1 (collector Q2) through the third winding of exciting transformer
T2. Next throug primary winding of main transformer T3 and capacitor C7 to the
virtual center of supply voltage.
Output voltage regulation
Output voltages +5V and +12V are measured by R25 and R26
and their output goes to the IC1. Other voltages are not stabilised and they
are justified by winding number and diode polarity. On the output is necessary
reactance coil due to high frequency interference. This voltage is rated from
voltage before coil, pulse-width and duration cycle. On the output behind the
rectifier diodes is a common coil for all voltages. When we keep direction of
windings and winding number corresponding to output voltages, then coil works
like a transformer and we have compensation for irregular load of individual
voltages. In a common practise are voltage deviations to 10% from rated value.
From the internal 5V reference regulator (pin 14 IC1) goes reference voltage
through the voltage divider R24/R19 to inverting input(pin 2) of error
amplifier. From the output of power supply comes voltage through divider
R25,R26/R20,R21 to the non inverting input (pin 1). Feedback C1, R18 provides
stability of regulator. Voltage from error amplifier is compared to the ramp
voltage across capacitor C11. When the output voltage is decreased, then
voltage on the error amplifier is too decreased. Exciting pulse is longer,
power transistors Q1 and Q2 are longer opened, width of pulse before output
coil is grater and output power is increased. The second error amplifier is
blocked by voltage on the pin 15 IC1.
PowerGood
Mainboard needs "PowerGood" signal. When all
output voltages goes to stable, then PowerGood signal goes to +5V (logical
one). PowerGood signal is usually connected to the RESET signal.
+3.3V Voltage regulation
Look at circuit connected to output voltage +3.3V. This
circuit makes additional voltage stabilisation due to loss of voltage on
cables. There are one auxiliary wire from connector for measure 3.3V voltage on
motherboard.
Overvoltage circuit
This circuit is composed from Q5, Q6 and many discrete
components. Circuit guards all of output voltages and when the some limit is
exceeded, power supply is stopped.For example when I by mistake short-circuit -5V with +5V, then positive voltage goes across D10, R28, D9 to the base Q6. This transistor is now opened and opens Q5. +5V from pin 14 IC1 comes across diode D11 to the pin 4 IC1 and power supply is blocked. Beyond that goes voltage again to base Q6. Power supply is still blocked, until he is disconnected from power line input.
Links
- http://www.belza.cz/swmodeps/compow1.htm
(Czech language only)
- http://www.belza.cz/swmodeps/compow2.htm
(Czech language only)
- http://www.epanorama.net/links/psu_computer.html
Computer Power Supply Page
- http://www.webx.dk/oz2cpu/radios/psu-pc1.htm
Power supply modification
- Franch
version in PDF thanks to Vincent MASSON
ATX Power Connector
|
Pin
|
Signal
|
Color 1
|
Color 2
|
Pin
|
Signal
|
Color 1
|
Color 2
|
|
1
|
3.3V
|
orange
|
violet
|
11
|
3.3V
|
orange
|
violet
|
|
2
|
3.3V
|
orange
|
violet
|
12
|
-12V
|
blue
|
blue
|
|
3
|
GND
|
black
|
black
|
13
|
GND
|
black
|
black
|
|
4
|
5V
|
red
|
red
|
14
|
PS_ON
|
green
|
grey
|
|
5
|
GND
|
black
|
black
|
15
|
GND
|
black
|
black
|
|
6
|
5V
|
red
|
red
|
16
|
GND
|
black
|
black
|
|
7
|
GND
|
black
|
black
|
17
|
GND
|
black
|
black
|
|
8
|
PW_OK
|
grey
|
orange
|
18
|
-5V
|
white
|
white
|
|
9
|
5V_SB
|
violet
|
brown
|
19
|
5V
|
red
|
red
|
|
10
|
12V
|
yellow
|
yellow
|
20
|
5V
|
red
|
red
|
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