Computer ATX SMPS No Power Repaired
Received one Desktop Computer for No power symptom.
Checked Power cable found OK, Checked power trigger switch on computer found OK .Checked Power supply Voltages on power connector there is no voltage output concluded the Power Supply is faulty.
For Triggering the SMPS you must have
Three Voltages on the Power Connector
1) PS_ON —- 5V ( Green Wire)
2) Standby —-5V (Purple Wire)
3) Power OK —-5V (Gray Wire)……..
Color Code of wire is Standard for
Any brand of PC Power Supply.
First I have Checked PS_ON Voltage I am getting no voltage. Hence I have Disassembled the SMPS for further fault finding. On Visual Inspection I didn’t found any Physical damage or burnt out.
Then I have removed the circuit from the Metal Chases.
Now I have started cold testing on Primary side…….But I am not getting any reading on multimeter. Even testing continuity on the trace it is not showing any Reading .so i turned the circuit on component side and checked Fuse for continuity
I found Fuse is OK and showing Continuity again I have tested on solder side same problem no continuity…………..
I have taken the circuit under bright light and see what I found……
Some Shiny liquid type substance on PCB primary side of the Circuit. On googling I found this is “PCB Non conductive insulating spray called Conformal Coating”.
A conformal coating is a thin polymeric film applied by spray to a printed circuit board (PCB) in order to protect the board and its components from the environment and corrosion.
So now I am comfortable for testing because I use sharp needle test multimeter probe I am just apply pressure on the test point to penetrate the needle to the solder.
Further ……as I have seen Fuse is intact and there is no burnt mark on PCB. It indicates that there is no short circuit on primary side & indicates some Open Circuit /malfunction of some components.
Checked 320V on Mains Capacitor found ok that means up to the mains capacitor everything is OK.
Hence I have decided to check further components on cold testing. I have removed two switching transistor checked found OK.
Removed Standby transformer side Diode because it gives reading on both the direction on PCB.
Testing Out of the Circuit it shows OK One direction Reading means Diode is OK. Now I have started checking all the components primary side after Mains capacitor. Here I found 1MΩ Resistor open circuit it is not showing any reading on the meter.
Replaced the faulty Resistor.
On tracing I Found this resistor is connected to the power management IC UTC 7608D Pin no. 1 assumed this is VCC PIN. (Didn’t found Datasheet on the net for UTC 7608D). After replacing new resistor I have re assembled the unit and reconnected the cooling FAN on the Circuit and turned on the power supply by triggering PS_ON Signal.
For triggering testing any PC SMPS you have to short the PS_ON (green wire) with Ground (Black wire) by putting ‘U’ clip copper wire.
For safety I have connected series Bulb and turned On the Unit. Now final result……….
So Culprit is 1MΩ Resistor.
Now Power supply is OK……..
One more thing… some technicians get confused for Cooling Fan Voltage.
Because in the PC SMPS mostly Red wire is dedicated to +5V and in FAN connector there is also Red wire. So whenever FAN gets BAD technicians cut the wire of new fan and connecting it on 5V. This is wrong.
Always check the voltage rating On the FAN it is 12V it should be connected to 12V.
This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.
P.S- Do you know of any your friends who would benefit from this content that you are reading now? If so, forward this website to your friends or you can invite your friends to subscribe to my newsletter for free in this Link.
Note: You can check his previous repair articles in the link below:
https://jestineyong.com/acer-es1-520-laptop-with-no-display-fixed/
(79)Dislikes
(0)
20 Comments
Leave a Reply
Parasuraman S
September 30, 2020 at 10:51 pm
Very thorough job with a lot of description step by step for even a layman to follow! Good job there! Many thanks for sharing!
Yogesh Panchal
October 1, 2020 at 3:26 pm
Thank You! Sir.
Josh
September 30, 2020 at 11:47 pm
Enjoying your posts.THanks for sharing.
Yogesh Panchal
October 1, 2020 at 3:27 pm
Your welcome Josh.
Albert van Bemmelen
October 1, 2020 at 12:04 am
Excellent repair! Sadly not all power supply connectors share the same common pinconfiguration anymore. The 18 pin connector for Medion (Aldi) desktop power supplies is completely different. And if another matching replacement supply can't be found we need to use a power adapter cable so we can use a standard 24 pin power supply in our desktop computer. Like this one for Lenovo 24 to 14 pin power connector adapter cable: https://www.amazon.de/-/en/CONECTO-CC20015-ATX-Adaptor-Supply-Motherboard/dp/B07CZ4LT2R
Yogesh Panchal
October 1, 2020 at 3:41 pm
Albert, Now a days Converters are available as you shared the link this majorly used in Business /Commercial series workstations & depends on type of the motherboard.
Greenford William Mafuleka
October 1, 2020 at 12:48 am
Dear Sir,
I have been not going through the articles because of too many things to do.I have one senior retired technician who started TV repair in business premise and he is very good on TVS. Will introduce him to you and that friend of you. The pc box power supply is good repair done, resistor problem solved.
Yogesh Panchal
October 1, 2020 at 3:42 pm
Thank you! Sir
Anwar Y Shiekh
October 1, 2020 at 3:33 am
Very, very nice catch; a 2c part.
Yogesh Panchal
October 1, 2020 at 3:43 pm
Thank you! Mr. Anwar
Alex Obara
October 24, 2020 at 5:20 am
Thanks Mr Panchal. Your work is awesome and encouraging.
babums
October 2, 2020 at 12:03 am
Your are very nicely explained to attend the fault.Thanks for sharing and excepting many more articles.
Yogesh Panchal
October 2, 2020 at 6:32 pm
Babums,
your welcome!
Humberto
October 2, 2020 at 11:04 am
Good explanations in your article and mission accomplished.
Yogesh Panchal
October 2, 2020 at 6:32 pm
Thanks! Humberto
Saqib Sami
October 6, 2020 at 2:30 am
Nice article Sir.
I have cooler master power supply, it does not show any output voltages.
When connected to 220v and tried to turn by connecting green and black wire, fan moves a bit only and there is hissing noise. What components should I check.
Yogesh Panchal
October 8, 2020 at 9:43 pm
Saqib Sami,
Just check hissing noise is from where?? from Fan or from the circuit to eliminate suspected stage first remove the "fan wire" if hissing noise is gone then either replace the Fan Or you can try it doing oiling in bushing. still have hissing noise check the capacitors and other components by method of cold testing using Multimeter. Remember to use series bulb while live testing.
solomon
October 9, 2020 at 2:05 pm
i have briefed with step by step explanation
keep the good work...and thank you a lot
Yogesh Panchal
October 15, 2020 at 3:45 pm
solomon,
your welcome!
Ray Floyd Plaza Cabrera
February 28, 2022 at 2:25 pm
Nice and detailed repair that helped me as a newbie. I had a similar generic 450w chinese PSU working for more than 10 years (unbelievable) with almost the same cheap parts and schematic.
The issue, it suddenly went out and when i checked i found 1 main capacitor open and also one mosfet E13007 shorted.
Replaced the two components and it worked!
Again, thanks for your tutorials.