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PC ATX PSU Quick Repair
In this document, I show you a repair article with high voltage sources. If you are not familiar with high voltage and or you have not the right tools, please do not repair this type of units. High voltage can damage your health even end in death.
Today a call comes down on my phone line from an accounting agency with a serious problem on their server PC where the databases of the customers are stored. The PC could not start and the other client computers could not work in the office because of no server problem. I moved immediately to the agency to see what is the problem and what is to do.
The server is a PC P4 with XP and with an MS SQL server installed on. Not a big deal but it does the job. In a few second I got the ride with the problem of the PSU, figured out does the PSU is bad. The agency has no other PSU for situation like this so I have to order one. However, it will take a day or so before it arrive. I decide to repair the PSU.
First, I checked for the version number of the PSU. This PSU is a Version 2.3 as you can see on the photo right in the table of DC OUTPUT MAX. These version numbers describe the typical construction of the PSU, which is an international regulation, and must fit the mechanical and electrical standards.
Here is a revision history of the PSU versions:
Version Release Date Notes
1.0 Dec, 1997 Public release
1.1 Apr, 1998
- Updated all mechanical outlines to clean up dimensioning of mounting holes.
- Added chassis cutouts for all mechanical outlines to clarify keep-out areas.
- Added Appendix C. 2.0 May, 2001
- Added SFX12V description
- Additional power ratings added
- Updated industry standards
- Increased standby current
2.1 Aug, 2001
- Section 4.4 Updated Figure 4 SFX/SFX12V Connectors
- Section 5.8 removed vendor name 2.2 Dec, 2001
- Section 3.23 Typical Power Distribution. Change minimum loading on 5V rail to 0.3A
- Section 3.3.2 PS_ON#. Add text “The power supply should not latch into a shutdown
state when PS_ON# is driven active by pulses between 10ms to 100ms during the decay of the power rails.”
2.3 April, 2003
- Reformat and update revision table
- Update Disclaimers
- Remove guidelines for SFX without 12V connector
- Updated power and current guidance
- Added efficiency targets for light and typical loading
- Increased minimum Efficiency at full load from 68% to 70%
- Updated guidance for standby efficiency
- Added Serial ATA connector
- Updated cross regulation graphs
This is ver.2.3 PSU, there are no big differences what the electronic stuff means.
My second and very minimalistic test was to disconnect the PSU from the motherboard and from all other devices, shorted the GREEN and BLACK wire wit a wire. The PSU started up immediately.
I was a bit surprised! I expected does the PSU will not power up, but…
After this test, I connected my Xilence PSU tester to the unit and see what is happening:
In real world, this type of testing is nothing than checking the voltages and the PG time. This type of tester are failed in lot of situation and do not detected a bad PSU even when a load is added on the PSU or without that. In other words, it is just a multi meter which can show all the voltages and the PG time on one screen on the same time. Do not expect too much from this tool.
Can you recognize the problem? Yes? ok, No? no problem. Check the zoomed picture of my tester. You can see four different voltages and one so called PG in ms.
Voltage 1: +3.3V
Voltage 2: +5V
Voltage 3: +12V
Voltage 4: -12V
The PG is the Power Good signal, which is measured in milliseconds or ms. Every PSU have a DC Voltage regulation, which shall remain within the regulation range. With or, without loads on the output connectors.
This is the DC output Voltage tolerance.
Here I made for you a DC output tolerance table, which you can use for almost every ATX PSU for PC computers. In most case, I use the reference guide made by Intel.
I got a measurement on my PSU tester on the 5VSB between 3.9v – 4.5v. This is outside of the tolerance table and makes the mistake. +5 VSB is a standby supply output that is active whenever the AC power is present.
This output provides a power source for circuits that must remain operational when the five main DC output rails are in a disabled state. Example uses include soft power control, Wake on LAN, wake-on-modem, intrusion detection, or suspend state activities.
Today’s modern motherboard has a so-called logic controlled power up circuit. Therefore, the power button is connected to the motherboard and not to the PSU as it was on the old type of PC-s. Because of this logic control circuit the PC can’t power on but without the mobo the PSU powered on when I shorted the green and the black wire on the PSU connector which goes to the motherboard. The next very important element to trouble shooting is the PG parameter.
The Power Good or by Intel PWR_OK is a signal used by the system power supply to indicate that the +5VDC, +3.3 VDC and +12VDC outputs are within the regulation thresholds of the power supply. If the PG signal timing is between 100ms and 500ms the PSU should be fine otherwise the PSU have some problems. As I realized does the 5VBS are in a bad range, the PG signal is in range with the other voltages I was sure does there is not a big problem. Lets see what was the problem:
Inside of the PSU. A bit dirty but nothing unusually or? I recognized a slightly swelled capacitor. I took my good old ESR meter, which is a homemade one and checked all the caps and this one too. After the checking of the caps, there was only one cap out of the range. This bulged one.
Here is the reading, LOŠ means BAD.
After this, I checked for shortened components or faulty one but nothing else was found. There was another small problem. A grinding noise, come out from the cooling fan unit of the PSU. After I disassembled the fan, and add some graphite grease, the grinding noise was gone. See the pictures below.
Cleaned the whole unit with compressed air and assembled it together. Here is the result:
After I put the PSU back to the server, it powered on and worked well.
You can find great ATX PSU repair guide from Mr. Jestine Yong on this web site: http://www.powersupplyrepairguide.com if you interested to learn how to repair these kind of equipments.
I use this technique to quickly identify the place or path of the problems in these kinds of units.
– short the green and any black wires on the connector when the PSU is out of the PC
– if PSU starts than you have no big problem
– if you have a PSU tester something like mine use them to measure the voltages and PG, if
not then use a usually multi meter
– check the results with the voltages output reference table from this article
– identify the faulty voltage and start checking the parts in that area
This article is for basic skilled repairer and novices in the world of PSU repairing.
For further learning of the technique of repairing PSU equipments please refer to the books by Mr. Jestine Yong who made a well explained repairing guides with great pictures and explanations.
I hope you will enjoy this article.
This article was prepared for you by Christian Robert Adzic from Novi Knezevac-Serbia.
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