PSU works, but connected to motherboard does not

[Escort Eagle]

Re: PSU works, but connected to motherboard does not

Originally Posted by re-atari:
In addition to the above: the other IC is a LM339. The combination TL494/LM339 was widely used in AT PSU's. They each cost just peanuts.

re-atari

But he has a Load taking Problem, Not volt Comparison .

[ciki022]

Re: PSU works, but connected to motherboard does not

domas

I follow Your suggestion to test it on the table, with "some" load.
I found two car light bulbs, one 45 Watts and other 21 watt, total 66 watts.
First I connected 21 watt light bulb, PSU started, and I measured just 12 V, it was 11.7 V
Then I connected both bulbs, and measured all voltages, results are listed :

+12 V 10.2 V
+5 V 5.09 V
+3.3 V 3.26 V
-12 V -11.9 V
-5 V -4.87 V

And suddenly BANG!!, something exploded, house automatic fuse goes off.
I disassembeld PSU and saw blown fuse and one of the rectifiers ( small part of the rectifier I put on the top of heatsink ), images attached

I have to replace these parts in order to continue testing, and I will also follow what Escort Eagle suggested ( check all three diode brackets - 12, 5 and 3.3 V )

[ciki022]

Re: PSU works, but connected to motherboard does not

I replaced blown fuse and rectifier, and tested other two rectifiers, one of them, located on the right side, crushed during dissasebmling, I also replaced him, tested PSU, and again BANG!!, fuse was blown again, but nothing else.
What to check now, what makes short circuit ?

[domas]

Re: PSU works, but connected to motherboard does not

okay, so you tested -12v with 66W of load? I guess it is rated for 2a max.
Thats why it exploded. I have done the same to my FSP psu, by overloading -12V to something like 4 amps.

My switching transistor would die after changing it because of shorted -12v rectifier diode. That is my thread about it https://www.badcaps.net/forum/showthread.php?t=28401

[ciki022]

Re: PSU works, but connected to motherboard does not

I visual checked psu again, and found next, images attached :
1. NTC power thermistor 5D-9 has almost invisible crack on it
2. Small ceramic condenser, usualy colored yellow, now is brown, marks are invisible, cracked in two halves, one "leg" on each peace, comparing size of other similar ceramic condensers, I concluded that mark was 102 1KV
With multimeter I checked all three rectifiers, and all is OK.
Also checked 4 diodes, marked 2A05, but one is bad, gives different measurment from other three, and I dont have replacement, and I cannot try does PSU after these replacements works
Should I check something else ?

[ciki022]

Re: PSU works, but connected to motherboard does not

I visual checked psu again, and found next, images attached :
1. NTC power thermistor 5D-9 has almost invisible crack on it
2. Small ceramic condenser, usualy colored yellow, now is brown, marks are invisible, cracked in two halves, one "leg" on each peace, comparing size of other similar ceramic condensers, I concluded that mark was 102 1KV
With multimeter I checked all three rectifiers, and all is OK.
Also checked 4 diodes, marked 2A05, but one is bad, gives different measurment from other three, and I dont have replacement, and I cannot try does PSU after these replacements works
Should I check something else ?

[ciki022]

Re: PSU works, but connected to motherboard does not

I just realized, about checking these 4 diodes, that in fact three of them are bad, one good.
This good one, when I measure it with multimeter, set to diode switch, red on anode - black on cathode, gives 549, other way around gives 1
These 3 bad diodes, gives 002-003, both ways measured
Can I find diodes that gives similar results when measured and relace all 4 ?

[ciki022]

Re: PSU works, but connected to motherboard does not

OK! Here we go ....... As you said when you are connecting 4 Pin Connectors that means +12V connector, then it is Load failing . I think, most probably +12V Diode bracket's one side is open . A diode bracket is consists of two diodes . One of the two diodes may be open . This is why +12V Diode bracket is failing to supply adequate Power when you are connecting 4 Pin Connector . Firstly Check that +12V Diode Bracket very carefully by removing from the PCB and be sure - Is it's one side is open or not . Then give a quick check to other +5V and +3.3V Brackets also .

If you found all outputs Diode Brackets are OK, then do this second job . In the controller section you have B494 Controller IC . If all outputs Diode Brackets are OK, then you have to change this B494 IC . You can use DB494/TL494/UV494/UVX494 anyone of these . You can use KA7500/KA7500B in substitute of B494 . Because TL494 and KA7500 are same .

Both steps Images are attached below . And show us what is the result ......

I have checked these three diode brackets, marked S16C40C - F10C20C - S16C40C, but not sure what readings should I get
I got these results :
S16C40C - measured with multimeter set to diode switch, black on colector, got 164 to both emitter and gate
F10C20C - black on colector, got 494 to both E and G

[Behemot]

Re: PSU works, but connected to motherboard does not

Lol, 450 W my ass

or a 55++W automotive light bulb

If you do that without thermistor, you will only blast out the +12 V rectifier, if it is not bad already. For fractions of second, it has startup currents of hundreds amperes.

[ciki022]

Re: PSU works, but connected to motherboard does not

I assembled PSU, but does not start at all, fan is not revolving, no voltage, fuse didnt blown

After two fuse explodings, i replaced next parts :
1. Two rectifiers 13007, with one D13007 and one E13007-2 ( first rectifier BU5027A, that refers to +12V is good )
2. NTC power thermistor 5D-9
3. Ceramic condenser 102 1KV
4. All 4 primary diodes 2a05 with R207

What should I check next ?

[ciki022]

Re: PSU works, but connected to motherboard does not

Lol, 450 W my ass

If you do that without thermistor, you will only blast out the +12 V rectifier, if it is not bad already. For fractions of second, it has startup currents of hundreds amperes.

I did that without thermistor and +12 V rectifier did not blast

[Behemot]

Re: PSU works, but connected to motherboard does not

Probably short protection kicked in. Sometimes it does, sometimes not. I've destroyed one rectifier like that, since than my load was equiped with termistor per each bulb.

[shovenose]

Re: PSU works, but connected to motherboard does not

You're fixing that piece of shit?
Pay shipping and I'll send you something better for free.
Edit: crap, you're not in the US. I have yet to figure out how to ship to AU from home let alone Serbia lol.

[ciki022]

Re: PSU works, but connected to motherboard does not

And what to check now ?

[Behemot]

Re: PSU works, but connected to motherboard does not

You do not even get +5 V SB?

Not sure what rectifier 13007 means, that's transistor, and I'd personally use same type from same manufacturer for both, there may be higher manufacturing differences if you use different ones. Those thing switch the power one at a time and they have to be equaly fast and so on.

[ciki022]

Re: PSU works, but connected to motherboard does not

Behemont
You are all right, that is not rectifier, that is power transistor, I apologize for that ( as You can see my mother language is not english, then serbian, and in all that translation of technical terms, I mixed up some things, and You also mentioned rectifier three posts before )
I will try to found same type of these 13007 transistors, and replace them
I replaced all 4 primary diodes 2a05 with R207, because I didnt found 2a05, but can I replace these diodes with kbp06 bridge rectifier ?

[senz_90]

Re: PSU works, but connected to motherboard does not

I have checked these three diode brackets, marked S16C40C - F10C20C - S16C40C, but not sure what readings should I get
I got these results :
S16C40C - measured with multimeter set to diode switch, black on colector, got 164 to both emitter and gate
F10C20C - black on colector, got 494 to both E and G

I just confused with this statement.
COLLECTOR, EMITTER and GATE??? when does schottky diode have these pins????

Do you know how to test schottky rectifier?? do you know how to test transistor? maybe you should let it go and throw to the garbage because you just waste your time without know what are you doing (maybe kill yourself) and that PSU is crap, really useless to waste much money changes that components. I am not smart enough on electronic to advice you (don't want to acting likes a genius or hero on electronic) but this maybe makes you consider about, if you just buy 2-3 caps or diode to replace for repairment it is okay, but after your BANG BANG accident, I think those are wasting your money on those crap PSU.

[ciki022]

Re: PSU works, but connected to motherboard does not

senz_90
I am learning, but like I said one post before, maybe is problem that english is not my mother language
Because of the fact that schottky rectifier is in TO-220AB package, similar to transistors, I used these terms C, E and G, instead of terms leg 1,2,3

I was going in electronical high school, computers and automatics, and later I finished Economics university, because of getting job

[senz_90]

Re: PSU works, but connected to motherboard does not

senz_90
I am learning, but like I said one post before, maybe is problem that english is not my mother language
Because of the fact that schottky rectifier is in TO-220AB package, similar to transistors, I used these terms C, E and G, instead of terms leg 1,2,3

I was going in electronical high school, computers and automatics, and later I finished Economics university, because of getting job

no, im still learn too, it's okay. and my english also bad nobody instantly to be a smart one.
I just wanna make sure that you know what are you doing, because SMPS more dangerous instead the linear one.
If you don't know how to test components properly, i suggest you read talkingelectronic site about test electronic component, I don't mind to share my ebook about test components, or with some effort you may find it on googling.

[Pentium4]

Re: PSU works, but connected to motherboard does not

You're fixing that piece of shit?
Pay shipping and I'll send you something better for free.
Edit: crap, you're not in the US. I have yet to figure out how to ship to AU from home let alone Serbia lol.

These are the best kind of PSU's to learn on If the projects fails, not much lost, if he succeeds, he's got a decent low wattage PSU.