Another one psu with only +5vsb output

[stefos]

Hello guys.

Looks like +5vsb output only is very common problem with atx psu.

First I had replaced three 10uf at 50v caps on primary side as esr was high. I give a try with light bulp and psu power on for 5 seconds all outputs and then shutdown. After then in every test I am getting only +5vsb.

As this psu is quite similar to previous fixed model, I changed the inductor coil but the problem did not fixed.

I have already made some voltages measurements at diodes, caps with esr, rectifiers etc.

Voltages at PS_ON state are:

KA7500C
=======
1: 2.7 mv
2: 4.868v v
3: 105.3 mv
4: 6.9 mv (3.369v on PS switching OFF)
5: 1.642 v
6: 3.620 v
7: 0.8 mv
8: 1.485 v

9: 0.8 mv
10: 0.8 mv
11: 1.478 v
12: 12.07 v
13: 5.023v
14: 5.023v
15: 5.023v
16: 08.mv


LM339N
===========
1: 3.844 v
2: 133.7 mv
3: 5.024v
4: 1.358 v
5: 502.mv
6: 1.4 mv
7: 2.687 v

8: 0.852 v
9: 105.4 mv
10: 2.208v
11: 115.5 mv
12: 0.7 mv
13: 2.8 mv
14: 2.8 mv

OPTO volatges (PS_ON state)
================
pin 1: 3.923 v
pin 2: 2.783 v

T2 transformer voltages (PS_ON state)
pin 1: 4.688 v
pin 2: 4.686 v
pin 3: 4.703 v

a) Green color at PS_ON state does not have any voltages, but on switching off state has 5.018 v

In image 387 marked the points I have already checked.

Can you please guide me what else can I check?

Thanks a lot.

[Escort Eagle]

Re: Another one psu with only +5vsb output

What is the voltage in PIN 4, 8, 11 & 12 of KA7500C IC in Off_State ? Also needed Voltage of T2 Transformer's PIN 1, 2, 3 in Off_State .

Also need a clear Picture of Image 387 without Text .

[c_hegge]

Re: Another one psu with only +5vsb output

That PSU looks like it runs seriously hot. Note the discolouration on the PCB. Did this PSU previously have its fan fail?

[PeteS in CA]

Re: Another one psu with only +5vsb output

450W? Maybe 250W, with those heatsinks, that main transformer, those input rectifiers and that inrush-limiting thermistor.

[senz_90]

Re: Another one psu with only +5vsb output

450W? Maybe 250W, with those heatsinks, that main transformer, those input rectifiers and that inrush-limiting thermistor.

Every PSUs with this 2 IC is very very common in 250W from my experience. those are cheap Chinese products that labeling 450W sh*t on their case.

For stefos.
It looks like your ground cable on mains transformer(the big one) is really bad burned. I would checks it If I were you. congrats on your repaired previously. I likes people with never give up attitude.

sometimes you will found there is one that post a thread and just WAIT for answer without effort likes make a voltage measurement, what he have checked and done.

[stefos]

Re: Another one psu with only +5vsb output

What is the voltage in PIN 4, 8, 11 & 12 of KA7500C IC in Off_State ? Also needed Voltage of T2 Transformer's PIN 1, 2, 3 in Off_State .

Also need a clear Picture of Image 387 without Text .

Hello friend.

I measured KA7500C IC voltages in Off_State and got:

pin 4: 3.367v
pin 8: 2.239v
pin 11: 12.36v
pin 12: 5.024v

also on T2 transformer pins (1, 2, 3) got 1.490v

Thanks !!!

[stefos]

Re: Another one psu with only +5vsb output

That PSU looks like it runs seriously hot. Note the discolouration on the PCB. Did this PSU previously have its fan fail?

Hi !!!

When i got the psu from a friend of mine was full of dust. Perhaps, the fan wasn't working well and at the time passed, appeared this discolouration on the PCB.

[stefos]

Re: Another one psu with only +5vsb output

Every PSUs with this 2 IC is very very common in 250W from my experience. those are cheap Chinese products that labeling 450W sh*t on their case.

For stefos.
It looks like your ground cable on mains transformer(the big one) is really bad burned. I would checks it If I were you. congrats on your repaired previously. I likes people with never give up attitude.

sometimes you will found there is one that post a thread and just WAIT for answer without effort likes make a voltage measurement, what he have checked and done.

Dear senz_90 thank you very much for your kindness.

I have one more same type main transformer and if needed i can change it. If it was faulty, it wouldn't faill the T2 transformer too (no voltages at all).

Stay cool !!!

[stefos]

Re: Another one psu with only +5vsb output

Hmm....If i short pin 4 with pin 11 of KA7500C psu works with light bulp showing no shorts.

[Escort Eagle]

Re: Another one psu with only +5vsb output

Are you shorting PIN 4 With PIN 11 or PIN 4 with Ground ??

[stefos]

Re: Another one psu with only +5vsb output

Are you shorting PIN 4 With PIN 11 or PIN 4 with Ground ??

I forgot to mention that found a broken sata cable and replace it. While i was looking at 7500c circuit, short pin 4 and 11 instead of GRD (test inputs) and psu worked. I remove the short and now psu still works. Tried with hd load and seems to be ok. I don't understand what happen but seems psu is ok.

[Escort Eagle]

Re: Another one psu with only +5vsb output

Hahahahaha ................. Very Interesting !! I have no idea what happened !! I am shocked too ..... !!

[goodpsusearch]

Re: Another one psu with only +5vsb output

wtf!

[senz_90]

Re: Another one psu with only +5vsb output

Maybe just a cold solder joint around the IC and you accidentally add a new solder and it works !!