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Computer PSU Repair

thisplayR66

Oct 10, 2023
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I have a computer PSU of Microsmart(cheap Chinese electronics company) having model no. MSP-450W. I was using the power supply as my lab bench power supply to power up my electrolysis setup. I accidentally shorted the 12VDC Yellow wire to Black ground wire. Before I could realize what I did, there was already a loud bang, it sounded like capacitor pop. So I decided to open up the power supply and replace the capacitor and any other component that was damaged, but to my surprise, there wasn't any sign of any damage. There wasn't even any black spot on the PCB anywhere. There was really loud bang that sounded like capacitor pop but not a single sign of damage. When I power the power supply, I do get 5V on Stand by and 2.3V on green wire(Secondary PSU startup wire) but there is no voltage present in +5VDC Red wire, +12VDC yellow wire. Unfortunately, I don't have schematic of the power supply which made finding anything about it hard for me. I saw some tutorials on youtube but they were quite unrelated to my problem. Given the situation, is there any specific location in my PSU where I can check for the fault. As far as I have looked, there seems to be only one fuse( fuse on mains wire which is good. Please help me with my situation! Thank you!

name.jpg

LVDC_side.jpg

HVAC_side.jpgtop_view.jpg
 

kellys_eye

Jun 25, 2010
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Check the devices bolted to the aluminium heatsinks - those that are located between the two heatsinks and not shown clearly in your pictures. It is probably the main rectifier for the 12V secondary side and is commonly a dual schotkky diode (in a single 3-pin package).
 

kellys_eye

Jun 25, 2010
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They would be the primary switching devices and the OP wouldn't measure diddly squat on any output if they were dud!
 

73's de Edd

Aug 21, 2015
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Sir thisplayR66. . . . . . .

With magnification notice soot on these two guys
WHUT !
you talkin' 'bout Willis ?
That's being nothing more than time related cumulative deposition of humidity borne California smog particulates.

What is the name of the control chip?
My 24in Swarovski crystal ball CLEARLY conjures the controller I.C. as being a Fairy-child . . . . .KA7500C . . . Korean knock off.

THEN . . . .
We can work with the 3 supplied photos, but you shortchanged us on the " schematic " of this unit . . .FYI . . . that's being a photo showing the foil side of the PCB.
Position to the center of the board and pan on in until the board just fills the screen then confirm no light reflections and then snap.
What are you electrolyzing? or just breaking water down into its 2 components , or even making Browns gas ?
Is there being provision for current consumption monitoring on your 12 VDC power feed.
If so, why not connect the main 5V supply in circuit instead of the present 12V one and evaluate the current consumption with 5V power and expect a little less than 1/2 current consumption then. Thus, confirming that you DO have a dynamic power level still coming out of that power supply . . . . . vice a static one. Or you could see the dequantified bubble activity now, comparative to the previous 12V operation.
Both the 12V and 5V supplies should have its dedicated winding of the SMPS power transformer feeding rectifier(s) and then an input filter cap and a series filter inductance and another final filter cap.
With a fully functional 5 V supply and your 12 V supply having had a direct short across it, I would be wanting to trace the YELLOW wire cluster pad back thru the foils involved in those previous lines of components I mentioned, looking for an opened foil point. Or run a LOW ohms test from Orange wires pad to the 12V output winding of the large switch mode power transformer.
Thaaaaassssit . . . .

73's de Edd . . . . .


You can tell a lot about a woman just by her hands . . . . . .
For instance, if they are around your throat, she's probably being slightly perturbed and upset with you.
.
 
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Delta Prime

Jul 29, 2020
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these two guys
WHUT ! you talkin' 'bout Willis ?
That's being nothing more than time related cumulative deposition of humidity borne California smog particulates.
Very well... three eyes against two... Trifecta!
Thank you for the correction Gary Coleman.
 
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thisplayR66

Oct 10, 2023
5
Joined
Oct 10, 2023
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Check the devices bolted to the aluminium heatsinks - those that are located between the two heatsinks and not shown clearly in your pictures. It is probably the main rectifier for the 12V secondary side and is commonly a dual schotkky diode (in a single 3-pin package).
Thank you! How do I access those without wrecking my PSU? Those bulky sinks and big transformer doesn't let me see a thing.
 

thisplayR66

Oct 10, 2023
5
Joined
Oct 10, 2023
Messages
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Sir thisplayR66. . . . . . .

With magnification notice soot on these two guys
WHUT !
you talkin' 'bout Willis ?
That's being nothing more than time related cumulative deposition of humidity borne California smog particulates.

What is the name of the control chip?
My 24in Swarovski crystal ball CLEARLY conjures the controller I.C. as being a Fairy-child . . . . .KA7500C . . . Korean knock off.

THEN . . . .
We can work with the 3 supplied photos, but you shortchanged us on the " schematic " of this unit . . .FYI . . . that's being a photo showing the foil side of the PCB.
Position to the center of the board and pan on in until the board just fills the screen then confirm no light reflections and then snap.
What are you electrolyzing? or just breaking water down into its 2 components , or even making Browns gas ?
Is there being provision for current consumption monitoring on your 12 VDC power feed.
If so, why not connect the main 5V supply in circuit instead of the present 12V one and evaluate the current consumption with 5V power and expect a little less than 1/2 current consumption then. Thus, confirming that you DO have a dynamic power level still coming out of that power supply . . . . . vice a static one. Or you could see the dequantified bubble activity now, comparative to the previous 12V operation.
Both the 12V and 5V supplies should have its dedicated winding of the SMPS power transformer feeding rectifier(s) and then an input filter cap and a series filter inductance and another final filter cap.
With a fully functional 5 V supply and your 12 V supply having had a direct short across it, I would be wanting to trace the YELLOW wire cluster pad back thru the foils involved in those previous lines of components I mentioned, looking for an opened foil point. Or run a LOW ohms test from Orange wires pad to the 12V output winding of the large switch mode power transformer.
Thaaaaassssit . . . .

73's de Edd . . . . .


You can tell a lot about a woman just by her hands . . . . . .
For instance, if they are around your throat, she's probably being slightly perturbed and upset with you.
.
Thank you for such a valuable answer! I am not a wizard of electronics and still learning a lot of things; comparing the foil side with upper side of PCB is really fascinating! I was trying to derust iron chains at that time so current consumption didn't really matter at that setup!
 

H2814D

Nov 4, 2017
211
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Nov 4, 2017
Messages
211
Check that transistor on the bottom right section of the PCB in your second and lowest picture in your first post. It looks like there is a hole in the top of it.
 

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73's de Edd

Aug 21, 2015
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thisplayR66


Bring on your money shot ! . . . . . . . . . the "schematic" side of the board closeup.
Considering that that transistor is physically /and/ circuitrally located where it is , I think that is just being some debris atop it
Moi . . . I . . . would be tracing from the YELLOW wire cluster to the first E cap located just above it and then to a related black filter inductor that it ties into and then out into another E-cap and then possibly thru 1 winding portion of that large ferrite toroid and then out to its PRINCIPAL rectifier(s) and then into the derived 12 V winding of the Switch Mode Power Transformer.

¿ ¿ ¿ Could there be anything worse, to try to keep constant good anodic contact with, other than a rusty linked steel chain ? ? ?
 
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Delta Prime

Jul 29, 2020
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¿ ¿ Could there be anything worse, to try to keep constant good anodic contact with, other than a rusty linked steel chain ? ? ?
WD-40? :)
@thisplayR66 you have to take those heat sinks off or at least another angle take a photo of the components attached to those metal fins called heat sinks please
 
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73's de Edd

Aug 21, 2015
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WD-40 is what you would NOT want on the activated chain links or in the electrolytic bath.


Having to use just the photo where the AC power cones into the board just above the fuse.
Look just to he left and you can see the left half of the units standby power transformer.
Deeper in to the left the LARGER main transformer is mounted at a right angle to it and just an edge shows and some nearby heavy 5V supplys wiring, covered with fiberglass sleeving.
I am expecting that heavy rear corner diode pair to be for your 5v supply. Then the pair of heat sink mounted TO-220 diodes to its right, will have one of them being used for your 12v supply.
Wheres our photo ?
 
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