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

[megantt]

hello everyone , working zebronics power supply 450 watts , 5v ,3.3v giving short to ground black wire, also in circuit at output, resistor was charred but shows right values , after removing resistors 39ohms at 3.3voutput, 51 ohms at 5v output, 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

 

[betwixt]

If you are sure its a short and not just low resistance between 3V3 to ground and 5V to ground, it implies you have cooked the rectifiers feeding those lines. They are the plastic T0-220 packaged devices screwed to the heatsink at the bottom of the fourth photograph. Note that it is normal for them to measure short circuit while fitted to the board, you have to unsolder them to test them.

It is unlikely but just possible that the reservoir capacitors on the 3V3 output have been overloaded if the 5V supply was shorted to 3V3, They tend to go low in value over time so it would be worthwhile changing them anyway.

Brian.

 

[KlausST]

Hi,

I think i don't have slow internet, but 19MB of pictures take it's time to download.
How slow it will be in regions with low internet bandwidth.
A different camera setup, the simples photo editing tool or an online photo editor would easily reduce file size to a total of 1MB without losing thread related informations...

Klaus

 

[megantt]

If you are sure its a short and not just low resistance between 3V3 to ground and 5V to ground, it implies you have cooked the rectifiers feeding those lines. They are the plastic T0-220 packaged devices screwed to the heatsink at the bottom of the fourth photograph. Note that it is normal for them to measure short circuit while fitted to the board, you have to unsolder them to test them.

It is unlikely but just possible that the reservoir capacitors on the 3V3 output have been overloaded if the 5V supply was shorted to 3V3, They tend to go low in value over time so it would be worthwhile changing them anyway.

Brian.

thank you for replying sir , i took out the resistors 51 ohm and 31 ohm, they beep in continuity , i got to know that smaller values resistors beep in continuity mode, i replaced the resistors(they beep too) ,still i get 5v to ground and 3.3v to ground continuity beeps , now i tested this with paper clips and a psu tester , the voltages are stable , the psu runs . when i connected the hdd sata cable to psu tester ,it showed 12 and 5v correct , nothing happend to psu tester , how can this be as 5v is grounded , is this safe to power a hdd ? someone was saying about protection circuit reset , i have no idea about it , also the other psu donest give this kind of beep continuity in 3.3 and 5 v ,its the same 450watt psu ,same company ,please guide me further . umm should i still change the rectifiers ?and yes those capacitors are little bulgy at top

 

[megantt]

Hi,

I think i don't have slow internet, but 19MB of pictures take it's time to download.
How slow it will be in regions with low internet bandwidth.
A different camera setup, the simples photo editing tool or an online photo editor would easily reduce file size to a total of 1MB without losing thread related informations...

Klaus

i am sorry sir , i dint know it came to be so big in size , i wanted the pics to be clear so it can be seen clearly and solve the problem , so next time i will have to check to reduce file size without changing its quality , thanks for the idea

 

[BradtheRad]

after removing resistors 39ohms at 3.3voutput, 51 ohms at 5v output, 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

Could these resistors provide bias to a defective device which shorts?

Are these resistors in a network (voltage divider, etc.) which delivers feedback to a defective device which shorts?

 

[megantt]

Could these resistors provide bias to a defective device which shorts?

Are these resistors in a network (voltage divider, etc.) which delivers feedback to a defective device which shorts?

thank you for replying sir ,i dont have idea about it , but its at output , called loading resistors ,which gives some load so the psu can give stable output voltages , i just learned it from several mentors.
the values are 5.01 v , 3.38 v , 11.87 v in paperclip test , and in psu tester ,it runs well, i get full 12v and other volts same . i ran for about few mins , the values are stable . anything i should test for more ?

 

[megantt]

i tried to plug in dvd writer and see how it goes , my pc is running in different psu , and i powered this dvd writer with this psu with out sata cable first , it ran ok, it opened all good , but when i put sata cable in dvd writer and switch on my computer the psu fuse is blown and i first dint know its a fuse , i tried it again , the spark came again at fuse site , what could be the reason for this ? all the voltages were good and stable but when i tried with sata data cable to computer , this happen , could it be bad sata cable ?

i opened , i found a little screw stuck to the first pair of diode track at back of circuit at input side ,sighs, but how did it work with the screw stuck back at circuit touching the case down ! but only when i put sata cable from computer to dvd writer , it went spark and blown fuse and now those 2 diode pairs too gone

 

[BradtheRad]

Obviously you have a bad cable which short circuits. Perhaps using it once led to further problems.

Many years ago we had rugged, durable connectors for computer peripherals. Centronics, SCSI, parallel ports. Within an enclosure there were IDE or PATA connectors. All had pins making it hard to install crooked.
Then USB (serial) connectors. Their construction continued rugged and durable.

I think tradeoffs were made with SATA, however. It appears flimsy especially if the manufacturer is careless. Conceivably an electrical tab can lift or come unglued from the assembly. Misalignment can result.

Did the employee who molds the wires to the connector allow the supply wires to slip against each other? With ingenuity you might hook up your meter so it lets you diagnose whether all wires go where they should.

 

[megantt]

is it the sata power cable or data cable caused it ?, because this short blown fuse happend only after connected the sata data cable , also that damm screw was touching that rectifier diode pair track at input side underneath the circuit ! when i opened the screws and flipped it , the screw was under it and also it charred a little the tract at tat place .
before i put it in dvd driver , i saw the sata power cable for its voltages and or if it has any shorts between 5v and 12 v , nothing was there... , the dvd writer run ,powered on normally .
should i have made a serial bulb test with this , could i have avoided blown fuse and diodes ?
also i checked the pins of dvd writer to see if it got any short after this has happend , its ok , i dint find any shorts .
"Did the employee who molds the wires to the connector allow the supply wires to slip against each other?" --- mm this wire is from the psu itself .
also does the sata data cable carry any power so its possible for it to short anything ?

 

[BradtheRad]

The screw rattling around could certainly short power anywhere unseen, then bounce elsewhere and cause another problem. Maybe in the sata power cable, maybe in the sata data cable.

You could solve one problem but there could be more problems you have to track down. This power supply might be more trouble than it's worth.

 

[megantt]

thank you for replying bradtherad , the missed screw was tightly held under the rectifier diode pair track line sticking to it , the screw wasnt moving inside .
so it took away the fuse , those 2 diode rectifiers .
i have almost checkd all teh other components , they seem ok , but i want to buy and keep those primary side npn power transitors etc , just in case ,also i plan to test with series bulb next time .
the transistors attached to heat sink are - 208c5027r 13007-0706 1300- 1012b
but i am unable to get these exact things online here at my place , what parameters mainly i should be looking when getting a replacements for these power transistors..