One more cheapy psu with +5vsb output only

[stefos]

Hello everyone.

Weekend is coming so I took in my hands one more psu T&P-MEIJI model: Meiji-350 ATX, but this time some components was burned, because fan was stuck. Temperature was increased and two inductors coils was burned.

First I have replaced the burned parts and also checked all capacitors with my esr meter, plus ic's, power FET's, diodes, two c945, A1015 transistors, tl431 regulator and tried to power on with light bulp in serial. No shorts at all but saw a common failure. Got +5vsb output only in psu tester.

I have already made some voltages measurements:

IC: S494P (PS_ON -----PS_OFF)
========================
1: 5.0 m v --- 6.2 mv
2: 4.853 v --- 4.854 v
3: 56.7 mv --- 56.4 mv
4: 3.402 v --- 3.720v
5: 1.656 v --- 1.653 v
6: 3.767 v --- 3.753 v
7: 1.3 mv --- 1.3 mv
8: 2.223 v --- 2.238 v

9: 1.2 mv --- 1.3 mv
10: 1.2 mv --- 1.3 mv
11: 2.222 v --- 2.235 v
12: 11.99 v --- 12.0 v
13: 5.088 v --- 5.090 v
14: 5.088 v --- 5.090 v
15: 5.088 v --- 5.090 v
16: 1.1 mv --- 1.2 mv


IC: S339P (PS_ON -----PS_OFF)
========================
1: 3.975 v --- 35.4 mv
2: 4.283 v --- 150.6 mv
3: 5.087 v --- 5.089 v
4: 1.363 v --- 1.367v
5: 3.735 v --- 1.24 mv
6: 1.9 mv --- 5.072 v
7: 2.692 v --- 2.695 v

8: 1.397 v --- 1.397 v
9: 58.8 mv --- 58.8 mv
10: 2.587 v --- 2.588 v
11: 254.6 mv --- 207.2 mv
12: 1.1 mv --- 1.2 mv
13: 1 mv --- 3.3 mv
14: 4.3 mv --- 8.4 mv

OPTO: (PS_ON -----PS_OFF)
======================
pin 1: 4.040 v --- 4.035 v
pin 2: 2.920 v --- 2.922v

T2 transformer (PS_ON -----PS_OFF)
============================
pin 1: 1.485 v --- 1.497 v
pin 2: 1.485 v --- 1.497 v
pin 3: 1.485 v --- 1.497 v

As you can see on T2 transformer both state voltages are equal. Is this normal or T2 failed?

Green color at PS_ON state does not have voltage, but on switching off state has 5.084 v.

When i shorted pin 4(DTC) with pin 7 (GRD) on S494P ic, the psu worked. Unfortunately is it not turning on in normal mode.

Where is the fan controller component? Since coils burned I want to replace it. Any more suggestions to make it work?

Thanks a lot for you help.

Nicholas

[stefos]

Re: One more cheapy psu with +5vsb output only

I have connected the ohmmeter up to the thermistor leads and watched the resistance from 6 ohm started to decrease with heat applied. Thermistor type is MD72-5D9. Can 1 ohm reduce the current and do not let psu powering on?

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

I hope those Diodes and Transistor are OK . Shown in "SS-01" .

Why don't you remove that +5VSB Resistor . Shown in "SS-02" . If it favors the Luck, then it could be run again like previous one !!

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

I have connected the ohmmeter up to the thermistor leads and watched the resistance from 6 ohm started to decrease with heat applied. Thermistor type is MD72-5D9. Can 1 ohm reduce the current and do not let psu powering on?

No, PSU running does not depend on Thermistor's resistance . And 6 ohms resistance of Thermistor is OK .

When you are shorting PIN 4 With PIN 7, then what is the Output voltage showing +12V, +5V and +3.3V and -12V ?

[stefos]

Re: One more cheapy psu with +5vsb output only

I hope those Diodes and Transistor are OK . Shown in "SS-01" .

Tested OK

Why don't you remove that +5VSB Resistor . Shown in "SS-02" . If it favors the Luck, then it could be run again like previous one !!

If i remove the registor the psu is working.

[stefos]

Re: One more cheapy psu with +5vsb output only

When you are shorting PIN 4 With PIN 7, then what is the Output voltage showing +12V, +5V and +3.3V and -12V ?

These are the values:

PS_OFF state : +9.42v, +5.83v, + 3.3.57v, -18.30v
PS_ON state : +12.90v, +4.946v, + 3.358v, -19.84v

Look like ther is a problem on -12v rail.

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

If i remove the registor the psu is working.

This is a exceptional totally disgusting design . Because of this design Every PSU creating the same problem in that same Point . Change that +5VSB Resistor with a new one and increase it's value at 3.3K and 1/2 Watt Resistor . Lets see what happens !!!

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

These are the values:

PS_OFF state : +9.42v, +5.83v, + 3.3.57v, -18.30v
PS_ON state : +12.90v, +4.946v, + 3.358v, -19.84v

Look like ther is a problem on -12v rail.

I do not understand What is the OFF_State and ON_State voltage in the Output !!!!! What do you mean by that !!!!!!

Your Output is increasing because You have changed the Inductor . New inductor is not matching with original one . New Inductor has different turns than original one . This is why 12V is going to 12.9V, 5V is decreasing to 4.94V and -12V is increasing to -19V .

[stefos]

Re: One more cheapy psu with +5vsb output only

I do not understand What is the OFF_State and ON_State voltage in the Output !!!!! What do you mean by that !!!!!! .

PS_ON = with psu tester
PS_OFF = without the tester

[stefos]

Re: One more cheapy psu with +5vsb output only

This is a exceptional totally disgusting design . Because of this design Every PSU creating the same problem in that same Point . Change that +5VSB Resistor with a new one and increase it's value at 3.3K and 1/2 Watt Resistor . Lets see what happens !!!

I found 4.5 k 1/2 W and tried without shorting pin 4 and 7.

PSU worked but +12v rail was around 6v and -12v rail increased -22.5v

Found 3.3 k resistor, but psu is not working. Only +5vsb

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

I found 4.5 k 1/2 W and tried without shorting pin 4 and 7.

PSU worked but +12v rail was around 6v and -12v rail increased -22.5v

PSU is working . It means You have a Load failing Problem of +5VSB Resistor .

+12V is decreasing to 6V . What about the Other Volts ?? Are they OK ??

Before changing the Inductor Change the 4.5K Resistor with original value 1K and watch what happens .

[stefos]

Re: One more cheapy psu with +5vsb output only

PSU is working . It means You have a Load failing Problem of +5VSB Resistor .

+12V is decreasing to 6V . What about the Other Volts ?? Are they OK ??

Before changing the Inductor Change the 4.5K Resistor with original value 1K and watch what happens .

With or without 1K registor i got almost equal values.
+12.90v, +13.05v,
+4.946v, +4.980v,
+ 3.358v, +3.380v
-19.84v, -19.90v

If i have to replace the inductor how do I choose the right one since previous one was burned?
Can i put a registor (what value and where on pcb?) and reduce the volts only in -12v rail?

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

Found 3.3 k resistor, but psu is not working. Only +5vsb

Does it working with 4.5K Only ?? Is it not working with 3.3K or 1K ??

[stefos]

Re: One more cheapy psu with +5vsb output only

Does it working with 4.5K Only ?? Is it not working with 3.3K or 1K ??

Works only 4.5k with wrong voltages output. +12v was +6v and -12v went to -22.5v.

[stefos]

Re: One more cheapy psu with +5vsb output only

Works only 4.5k with wrong voltages output. +12v was +6v and -12v went to -22.5v.

Witk 22.11K registor on +5vsb fixed +12v output (got 12.85v). Also +5v and +3.3v was ok. Left only -12v where stack at -18.60v

Where can i put a registor to drop the voltage on -12v rail?

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

It has been created a big Problem by changing the Inductor !!! Is that original Inductor Totally unusable ??? Do you not have any same PCB ??

Another Way - From which PCB have you taken that Inductor ? Can you give me a Picture of that PCB ? I mean - If the Output Volt rails (+12V, +5V and +3.3V) of that Main Transformer from which you have taken the Inductor are similar with this Problem PCB's Main Transformer Volt rails, then you can replace this Transformer with That Main Transformer . Because this Inductor is designed with that Transformer . By replacing Main Transformer I think It can solve the Voltage Problem . I hope that Transformer is similar with this transformer . If they are not same then how can you change the Inductor !!

Second Way - From which rail -12V has taken ? Is it from +12V or +5V rail ?? If it is taken from +12V rail then take the Inductor's input from +5V rail . I think it will fit the -12V OK, because this inductor's -12V was taken from +5V rail .

Third Way - Your PSU is 350W, so this -12V should not use more 500mA current through -12V rail . You can use a LM7912 negative regulator to regulate the -12V .

By the way - As your -12V is going higher, then Is Your PSU Tester detecting it and making any Error Beep ?? or showing it is OK !!

[stefos]

Re: One more cheapy psu with +5vsb output only

It has been created a big Problem by changing the Inductor !!! Is that original Inductor Totally unusable ??? Do you not have any same PCB ??

The original inductor was burned and unfortunately don't have similar pcb.

Another Way - From which PCB have you taken that Inductor ? Can you give me a Picture of that PCB ? I mean - If the Output Volt rails (+12V, +5V and +3.3V) of that Main Transformer from which you have taken the Inductor are similar with this Problem PCB's Main Transformer Volt rails, then you can replace this Transformer with That Main Transformer . Because this Inductor is designed with that Transformer . By replacing Main Transformer I think It can solve the Voltage Problem . I hope that Transformer is similar with this transformer . If they are not same then how can you change the Inductor !!

The inductor was taken from another pcb with one IC and rails does not match. Tookd transformer and inductor from the other pcb but when turn on psu i got short in light bulp. So resolder back the original transformer.

Second Way - From which rail -12V has taken ? Is it from +12V or +5V rail ?? If it is taken from +12V rail then take the Inductor's input from +5V rail . I think it will fit the -12V OK, because this inductor's -12V was taken from +5V rail .

I am little confused with this option. I uploaded an image with inductors voltages. Can you show me on image how can this be done?

Third Way - Your PSU is 350W, so this -12V should not use more 500mA current through -12V rail . You can use a LM7912 negative regulator to regulate the -12V .

If i buy LM7912 regulator where should be connected on pcb schematic?

By the way - As your -12V is going higher, then Is Your PSU Tester detecting it and making any Error Beep ?? or showing it is OK !!

I don't get any sound from psu tester but lights on +12v and -12v are quite brightly.

This psu is quite old and the pcb has been a mess after all this testings. If there is an easy option I give it a try otherwise I' ll keep it for parts.

Thanks !!!

[kaboom]

Re: One more cheapy psu with +5vsb output only

The original inductor was burned and unfortunately don't have similar pcb.



The inductor was taken from another pcb with one IC and rails does not match. Tookd transformer and inductor from the other pcb but when turn on psu i got short in light bulp. So resolder back the original transformer.




I am little confused with this option. I uploaded an image with inductors voltages. Can you show me on image how can this be done?



If i buy LM7912 regulator where should be connected on pcb schematic?




I don't get any sound from psu tester but lights on +12v and -12v are quite brightly.

This psu is quite old and the pcb has been a mess after all this testings. If there is an easy option I give it a try otherwise I' ll keep it for parts.

Thanks !!!

With the replacement inductor, are there the same number of turns on the winding for -12 as there are for +12?

The -12 winding will be smaller wire, but should have the same number of turns as the heavier winding for +12.

The peak voltage before immediately after the rectifiers is around 20V for the 12V outputs. The duty cycle is varied, and the output inductor integrates the constant amplitude-variable width pulses into your +/- 12V.

If the replacement inductor has too few turns or too small/wrong material (most are -26 or -52), the inductance will be too low. You'll then lose the integration of the inductor, particularly at light loads.

Also, peak primary current will increase, as well as the current through the first secondary filter caps.

[Escort Eagle]

Re: One more cheapy psu with +5vsb output only

1. Remove those three Connections From PCB . [Shown in "SS-03"]

2. Then Connect those Two Pins with a Jumper . [Shown in "SS-03"]

Lets see what happens ....

[stefos]

Re: One more cheapy psu with +5vsb output only

With the replacement inductor, are there the same number of turns on the winding for -12 as there are for +12?

I could not verify because original inductor was burned at all and throw it.

The -12 winding will be smaller wire, but should have the same number of turns as the heavier winding for +12.

Your advice was helpful, because I have noticed that thinner wire was first in place. I soldered again in correct (I hope this time) sequence and I got back -12v in inductor -12v output. Unfortunately when I add HD load PG light went off in my pSU tester.