HomeMade Testers Were Used In Testing Power Supply Components
This repair was put aside for a long time when I was unable to fix the not working Fan. After I had tested all semiconductors and components, including the e-caps before. Until today when I reopened the unit for another check! And maybe for the 3th or 4th time!
The Fan itself was working fine but it never started in this Corsair VX450Watt power supply. And although I managed to get the Fan running by heating up the components on the mainboard it never worked on its own. The Fan only worked when I heated up the transistors in the circuit around Q901 and R901. But they checked all fine when checked with my DCA75 and other semiconductor testers. But I will come to that later because when I rechecked the already previously made photos I noticed something odd I had not checked before! (remember that this is an important break-through in fixing this Power unit!).
This power supply was given to me because it failed working correctly in the desktop computer of my friend’s neighbor. And all my Power supply Testers tested the output voltages of the Power supply being correct. Only the -5V led on the testers doesn’t work simply because the Corsair doesn’t produce any -5V output voltage.
I even made a special TL431 tester that also can test the optocouplers at the same time and tested the TL431 with that fine tester to make sure my other TL431 testers were all giving the correct same good results! And this repair will show all steps I took to successfully fix the not working Fan.
Following photos show the results as given by all my power supply testers (3 of them!) I have that confirm that all outputs are working splendidly. So they do not check on the not working Fan in the unit and are no help in fixing the still not safely working Corsair VX450W!
Previous photo above showed my third and latest power supply Tester. And the already rotating Fan after I managed to fix the not working circuit this repair is about. Only the -5V led never works because the Corsair as mentioned doesn’t have a -5V output.
Next photos show the 12V Fan connector next to Q901, R901 and the other transistors, plus the solder side of the board. I had previously tested ALL semiconductors plus the e-caps including the SS8050 transistors Q901 and resistors that all checked out being okay. Including the semiconductors on all Cooler plates, which are always the easiest to check by removing the entire Cooler plate from the board for further inspection. (so without the need having to remove each and every single semiconductor from the plates at all! And so saving much time when placing them back into their positions on the board). I marked the transistor position Q901 by a blue circle and will now explain why I before wasn’t able to find the culprit why the Fan in this Power supply still wasn’t working.
Therefore I will show some of the previous made photos I took after I had checked these semiconductors before. And please notice the very low Hfe value on my DCA75 Tester of only 18! Something I previously had overlooked! Today in a hunch I remembered not having checked these values at all! So I compared the value I had a snapshot taken from with the values in the SS8050 datasheet. The minimum Hfe value should be about 45 which it never was! And because they normally are much higher I removed Q901 for another check now many months later! And you probably guessed it. The transistor was no longer working and had became a diode! Why I removed it and immediately replaced it by a new SS8050 40V 1.5A transistor.
You can click on the above picture to access the Datasheet
In the next photos the 8050 Q901 position is shown. The HY-510 chip on the vertical board is for modern energy control purposes and so has nothing to do with our not working Fan. After Q901 was replaced which was the hard to find culprit, the Fan finally worked at once!
Previous last 2 photos showed Q901 then and now! Gone from a ‘working’ transistor with Hfe 18 to a BaseCollector diode. (emitter contact is no longer working!).Probably because the max CBO voltage is 60V opposed the the lower max 25V of the CEO of this 1W transistor.
Below the perfect working TL431 + PC817 optocoupler tester I made and used to check the TL431 on the board of this Corsair VX450W supply. It can be found in one of the many Youtube videos and the 3 leds, Blue, Green and Red show a right working sequence when the optocoupler and the TL431 under test are working fine while we turn up (and vice versa down) the input DC voltage between the + and 0 (gnd) connections.
And next photo shows my Elektor Opamp tester I made and use to test single, dual and quadro Opamps. (All at the same time under test if needed!). It can’t test the special Comparator Opamps that exist but a lot of Opamps if not almost any of them.
The last photos show the component side of the Corsair VX450W. And the entire board solder side.
Conclusion: never expect any measured value to be in their in the datasheet given range! It could have saved me a lot of time in finding the culprit! I now was only able to find the cause because I rechecked my previous findings.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: