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No power supply

Dc volt ok and str ok and no power supply out

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The DC voltage may be OK but if the inside gas in the tubes is compromised then it won't make a difference. Trying a higher voltage may do the trick or placing a piece of aluminum foil in back of the segment may also do it, but remember what I said about leaving it on for a prolonged time with the higher voltage.

Posted on Mar 30, 2014


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Fault finding

Power is going to the motherboard, and you know this by assuming?

An assumption would be you see the Power Supply fan spin, LED lights light up, and maybe computer case fans spin.

Not an assumption, and you would have tested the 3 main voltage power rails, coming out of the Power Supply.

The Power Supply in your computer is an SMPS.
Switched-Mode Power Supply. (Also is known as the short abbreviation - PSU. Power Supply Unit)

The Power Supply in your computer is a Converter.
It converts HIGH AC voltage into 3 LOW DC voltages.

[Depending on country,
USA = 120 Volts AC. UK = 240 Volts AC. Japan is 100 Volts AC, but may depend on area. Australia = 240 Volts AC. India = 240 Volts AC. HOWEVER, do not write the above in stone. I may have made an error ]

The 3 low main DC Voltages coming out of the Power Supply is;
A) 3.3 Volts DC
B) 5 Volts DC
C) 12 Volts DC

Orange wires carry 3.3 Volts DC
Red wires carry 5 Volts DC
Yellow wires carry 12 Volts DC
ALL Black wires are Ground wires. They can also be called Negative wires.
This is a DC circuit now. There is a Positive, and a Negative.
Orange, Red, and Yellow wires are power wires, and also Positive wires.

The first part of your diagnosis will be to test those 3 main voltage power rails.

Using an example;
There are many Red wires coming out of the Power Supply.
These are 5 Volt wires. They are Connected TO, the 5 Volt power rail in the Power Supply.
ALL 5 Volt wires end in one place, in the Power Supply.
The 5 Volt power rail.
When you test just ONE red wire, you are testing the entire 5 Volt power rail coming from the Power Supply.

This also goes for the Orange wires, and Yellow wires ]

With the Red 5 Volt wires, and Yellow 12 Volt wires, you could just use a 4-pin Peripheral power cable to check them,

Multimeter set to DC Voltage, the red (Positive) probe lead of the multimeter; touches the female metal terminal connector, for the Red wire.

The black (Negative) probe lead of the multimeter, touches a female metal terminal connector, that goes to a Black wire.

You should be reading 5 Volts DC.

Same thing for the Yellow 12 Volt wire.

With an Orange 3.3 Volt wire, this changes.
A straightened out paperclip is inserted, down into the BACK of the ATX main power cable's connector; AND into a socket hole with an Orange wire in it.

The straightened out paperclip, slides down into the socket hole, with the Orange wire in it.
Slides down into the socket hole, RIGHT NEXT TO the orange insulation of the wire, and MUST go down far enough; to Touch that female metal terminal connector.

EVERY wire going down into the ATX main power cable's connector, ends in a female metal terminal connector.

Same thing is down with a socket hole that has a Black wire in it.
ALL Black wires are Ground wires. (Negative)
You can choose ANY socket hole that has a Black wire in it.

Now touch the two probe leads of the multimeter, to their respective straightened out paperclips.

Red (Positive) probe lead of multimeter, to straightened out paperclip in Orange wire socket hole.
Black (Negative) probe lead of multimeter, to straightened out paperclip in Back wire socket hole.

You should be reading 3.3 Volts DC.

(Or if your multimeter kit has special probe lead, that would take the place of a straightened out paperclip, of course use it instead)

Know this;
A) If ALL of the LED's ('lights') were on at once, they would use less than 1 Watt of power.

B) EACH fan uses 2 to 3 Watts of power.

C) A typical CPU (Processor) can use 51 to 130 Watts of power.
Just depends on what Processor (CPU) it is.

This is why a Power Supply with a weak voltage power rail, will not have enough power to turn the Processor ON, but will have enough power to light those simpy LED's, and spin fans.

[LED - Light Emitting Diode ]


May 11, 2013 | Dell Computers & Internet

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Power failure of motherboard

"power failure of motherboard"

I'm lost. Since when does a motherboard produce power?

Power failure AT motherboard?

You have tested the 3 main voltage power rails, coming out of the Power Supply?
A) 3.3 Volts DC
B) 5 Volts DC
C) 12 Volts DC

[In comparison two D cell flashlight batteries produce 3 Volts DC ]

[ From ]

ALL Orange wires are 3.3 Volts
ALL Red wires are 5 Volts
ALL Yellow wires are 12 Volts.
ALL are DC Voltage

ALL Black wires are Ground wires. Means Negative wires. ( - )
All power wires named above are Positive wires. ( + )

(This is a DC circuit)

Positive (Red) probe lead to power wires, one at a time.
Negative ( Black) probe lead stays connected to ANY Black wire.

Looking at the Playtool link, observe the photo to the Right.
Shows 24-pin ATX main power cable plugged into motherboard.
This is what you want.

The Back of the connector is where the wires go in.
The Back of the connector, is where the straightened out paperclip goes in.

I straighten out a paperclip, and insert down into the socket hole; of the power wire to be tested.

(Orange, or Red, or Yellow)

Straightened out paperclip, slides RIGHT NEXT TO the existing wire.

Look at middle photo. See the Front of the connector? You can barely make out the ends, of the female metal terminal connectors.
This is a closer look,

At the bottom of the photo is the Front; of the female metal terminal connector.

At the Top is the Back of the connector.
The straightened out paperclip, MUST slide down into the socket hole; far enough to touch the Back of the connector.

Now do the same for ANY Black wire.
Power Supply now plugged into power, you can now touch the multimeter's probe leads, to the straightened out paperclips.

Two paperclips used at one time.
Test each voltage power rail, one at a time.

When I state Voltage Power Rail;

3.3 Volt power rail.
ALL of those Orange wires end at one central point, in the Power Supply; the 3.3 Volt power rail.

This means you can test ANY Orange wire, and be testing the 3.3 Volt power rail.

Same goes for the 5 Volt power rail. (Red wires)
Same goes for the 12 Volt power rail. (Yellow wires)

What are the voltages? Post back in a Comment.

Use a KNOWN to be good, Compatible power supply; for a temporary test unit.

Power Supply checks out OK, or you are using a KNOWN to be good, Power Supply?

What do the Electrolytic Capacitors look like? See any bad ones?
(Radial Aluminum Electrolytic Capacitor)

For additional questions please post in a Comment.

Mar 25, 2013 | Gigabyte GA-M61VME-S2 Motherboard

2 Answers

Wht kind of current comes out?

The computer's switch mode power supply produces DC (direct current) electricity.

Nov 05, 2012 | Computers & Internet

1 Answer

Have Eiki LC-X1000 projector. Recently had a power outage and since then it has not come back on. Have tried the reset, 230 AC ok and 300 DC volt ok, No standby light, nothing,then what can i do

dried out smd capacitors in primary part of power supply , common problem with this and similar models. 1uf, 2.2 uF and 1 radial 220 uF
replace bij 105 oC type

Apr 05, 2012 | Eiki LC-XG250 LCD Projector

1 Answer

Power supply problem in matsui tvr180, in STR section, can u please suggest me the circuit diagram to rectify my problem

The power supply, from memory, uses an STR type power supply chip and is controlled by use of an opto coupler.
In my experience the opto couplers hardly ever give trouble, nor the STR's if caught in time.
Change the capacitors around that part of the board within the hatched area especially look out for 22 or 47uF 35 Volt start up capacitor.
Hope that helps but the models changed from week to week depending on which factory the ubits came from.

Jan 01, 2011 | Televison & Video

1 Answer

Hitatchi 42pd5000 will not power up

pls. open H-output trangister and out side of pcb and check voltage B+ 135v dc is ok ?.
if yes.then ...H-OUTPUT trangister checked and replace
if not then check SMPS .
3.output Dyode
1st fuse is open then check rectifier dyode cantunity. if sort then replace all 4 dyode.(rectifier)
and if dyode is ok .then check STR cantunity is sort then Replace with New STR but 1st 220uf/450v dc capaciter cheked / 2nd. in SMPS stage any P.F and capciter likage or sort cheked or chenged first after the NEW STR use
*. note: smps pcb checkd any dry canaction pls. Resolder first.

Oct 04, 2009 | Hitachi Televison & Video

1 Answer

I have a newer sony receiver that suddenly had the same problem

The display operates on ac and dc voltage. The outer pins on the display should read approx. 3 to 5 volts dc.It might read more. If the circuit traces are good to the transformer the ac will be there. The dc is supplied by a zener diode. The zener diode is shorted or breaking down. This will cause a dim display. Follow the display's outer pins circuit traces to locate the diode and verify the circuit traces are not broken as these lines sometimes are run down the edges of the boards. The edge of a board is a popular place for a board to have a crack and break some traces. Good luck, barneyluc

Sep 25, 2009 | Sony STR-DE345 Receiver

1 Answer

Makes an loud clicking/popping sound

The audio outputs are intermittently shorting to their supply and allowing DC voltage to pass - the speakers will be damaged if it continues. you can confirm this by measuring (with a dc voltmeter)at the speaker outputs for DC volts.

Sep 19, 2009 | Sony STR-DA50ES Receiver

1 Answer

No power

check voltage at the primary filter then check voltege at pin no 1 of STR dc which should be approx input volt if not then clear the path if present then check check up down volt at pin no 3 if not persent then replace the small capacitor near it the problem will be solved

Sep 10, 2008 | Compaq FS 7550 17" CRT Monitor

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