Question 450watt power supply 5v, 3.3v short to ground wire,in output rail ,connectors

[meganin]

hello everyone , working zebronics power suply 450 watts , 5v ,3.3v givin short to ground black wire, also in circuit at output, resistor was charred but shows right values , after removing resistors 39ohms, 51 ohms, there was no short , no continuity beeps with ground , but after replacing new resistors (now i am not switching it on) ,again short still exists . when i put bigger ohm resistor like 100k ohm , no short beeping sound comes , lower ohm resistor gives continuity beeps ,other big ones donest , as its a working psu , i am confused what to remove now or how to go further now .
how this happend - i was putting a bad sata cable extension which blew the 12v/5v diode(not sure) in hdd pcb ( repaired it -working now) and made this short in psu , how to remove the short , thank you .what problem this short can cause to mobo and hdd ? i am not sure this short caused hdd 5v or 12 v diode break or the bad hdd sata cable caused this , but when the hdd gone bad , the other 2 hdd were working normally and computer was still power on , i checked the power cables black wire(ground) short with red wire (5v ) , then short with 3.3v orange wire , i know this is not normal , so i dint put this psu again in my computer ,i wana remove the short, guide me , thank you

 

[mindless1]

I am not sure what to make of your description which does not clearly describe the situation well enough to be certain what is going on.

The larger resistors on each rail are probably load resistors, as the PSU needs a minimal load to have stable output, so it would be normal for them to read continuity between the power rail and ground. I am a bit puzzled that you do not notice this from looking at the back of the circuit board. Is it possible that this repair is beyond your skill level?

At the time of the fault, did you unplug the PSU from AC mains, wait a few minutes then plug it back in to try it? It may have invoked the protection circuit and only needed that time to reset and work again. Also check the fuse.

If you had done that, I would work my way backwards from the output, checking all the power (high current) handling semiconductors.

I would now investigate the diodes on the heatsink in your last picture, and if they are good, then the large transistors on the other heatsink... keeping in mind that this transistor heatsink is probably live (electrified) at high voltage when the PSU is turned on. Next check the bridge rectifier diode(s) just before the large, high voltage capacitors on the high voltage side.

How old is this PSU? From what I see in the pictures, it is not a very good PSU and may not be worth the time and parts cost to repair.

 

[meganin]

thank you for replying ,yes sir, its load resistor ,39ohms at 3.3v , 51 ohms at 5v , gives continuity beep sounds with ground , i checked at back of circuit , each resistor is connected to ground track . at the time of fault happend , one of the hdd 5v or 12 v diode in its pcb was burst , with working pc and other 2 hdd at the same time, then i removed everything , the same psu runs the computer again well with other 2 hdd but i am afraid to use it, so i replaced with other psu .
so how this short can be solved ? is it ok to run hdd on this psu if this short persists ? there is no short in 12v line , but at 3.3 and 5 v line short exists .
the other psu dont have this short at 3.3 v adn 5 v line , so i am trying to know about these and take off the shorts

 

[mindless1]

As I attempted to explain, based on what you written, I am not recognizing any fault condition detected, that it would measure continuity between the power rail and ground over each respective load resistor.

If you keep it unplugged from a computer and short the PS_On wire to a ground wire, does it stay turned on and suppling correct voltages on the outputs? If it does then I would attempt to use it again if you must, but if the system or data is valuable, I would not trust it due to it being a low quality PSU to begin with.

 

[meganin]

ok sir , i will check the voltages with paper clip test and come back .

 

[Hans Gruber]

ok sir , i will check the voltages with paper clip test and come back .

While you doing that. Find a 20oz carpenter hammer and give it a few whacks before tossing it in the garbage can. It's better to be safe than sorry. You do not want to create a fire hazard by attempting to repair a power supply.

 

[meganin]

As I attempted to explain, based on what you written, I am not recognizing any fault condition detected, that it would measure continuity between the power rail and ground over each respective load resistor.

If you keep it unplugged from a computer and short the PS_On wire to a ground wire, does it stay turned on and suppling correct voltages on the outputs? If it does then I would attempt to use it again if you must, but if the system or data is valuable, I would not trust it due to it being a low quality PSU to begin with.

sir i checked it , the values are 5.01 v , 3.38 v , 11.87 v in paperclip test , and in psu tester , i get full 12v and other volts same . i ran for about few mins , the values are stable .
why the psu tester dint go bad when i put the sata hdd cable as in it the 5v and ground shorts ,it showed all the values correct . so is the protection circuit is gone , what should be done to make the protection circuit back on ..
this psu is made in india , its a year old other psu are very expensive, local shops only have this mostly .

 

[mindless1]

I still can't understand what you are describing, besides that right now it appears to be operating normally.

Can you clarify what makes you believe that, or wonder if, the protection circuit is gone?

If it is supplying 5.01V, 3.38V, and 11.87V with no load, next it is time to give it a computer as a load to see if the voltages remain stable.

If over time, your load resistors, heating up has caused poor solder joints, or your troubleshooting has caused them to be poor like I see in the picture of the back of the PCB, then you need to resolder those areas. I have identified several questionable solder joints on the picture you provided. There may be more questionable areas that I can't discern from the picture.

 

[meganin]

yes i was having trouble with solder , i fixed them now . umm i dont know about the protection circuit clearly , other psu dint give this continuity in 3.3 and 5v cables , earlier you mentioned about it -- "It may have invoked the protection circuit and only needed that time to reset and work again." .. so i doubted if anytihng happend to some protection thingy.. or may be the other psu is designed differently .. sorry for messing up too much sir . ^^

 

[BoomerD]

Replace the power supply with a better quality unit...and HOPE nothing on the motherboard was damaged when the cheap one went bad.

 

[fralexandr]

Wow, I took a look on amazon.in and the basic 450w zebronics can only handle ~220w max on the 12V rail.

 

[meganin]

ya

Replace the power supply with a better quality unit...and HOPE nothing on the motherboard was damaged when the cheap one went bad.

many are saying this zebro is dirt design , i gotta buy a better one with emi ..

 

[meganin]

Wow, I took a look on amazon.in and the basic 450w zebronics can only handle ~220w max on the 12V rail.

umm i have asus p5ql pro 3 hdd , 2x 7200 rpm , 1 x 5000 something . x5470 cpu (modded) -120tdp , zotac ddr5 1 gb nvidea gt730 , 2 case fans , cpu cooler antec a40 120 mm fan i guess, 4x ram ddr2 7gb total . i am not using the psu in discussion but i am using the same zebro tho , in local we get only these more often , so got this for now and running, i dont run any intensive softwares or stress test by the way.
been using the same thing for nearly 5 years may be now. the psu which gone bad was due to my sata power cable misshappen by myself tho..

 

[serpretetsky]

Sorry for late reply. From my understanding you have determined that the supply lines are shorted to ground based on continuity test? I dont believe this is conclusive. Continuity test beeps whenever the multimeter measures a resistance below some arbitrary resistance. It seems your multimeter considers 50 ohm resisters as shorts, which in this case is useless information. I would say there might still be something wrong with your PSU (i cant tell), but the resistors seem ok. I don't see resistors fail very often, but when they do they usually fail open (higher resistance than normal, not lower).