Author Topic: Help with dead AT PC Power Supply  (Read 2843 times)

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Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #25 on: October 08, 2024, 06:13:52 pm »
Ok, I used IPA on the PCB and touched it, but nothing is getting warm.
The bench PSU draws only 0.031A.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #26 on: October 08, 2024, 06:21:56 pm »
Increase the voltage step by step to get 1W consumption. Maximum limit is 12V.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #27 on: October 08, 2024, 06:27:47 pm »
Ok, the biggest IC on the board is getting warm.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #28 on: October 08, 2024, 06:35:47 pm »
This is PWM controller itself. Probably internal zener diode is broken.
Try cleaning the black stuff off the chip top to clarify its name.
« Last Edit: October 08, 2024, 06:37:48 pm by Harry_22 »
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #29 on: October 08, 2024, 06:58:13 pm »
Ahhh I was hoping the black stuff is some kind of plastic shrink warp, but the material is almost like the body of an IC.
I tried to scrape it off, but the model number of the IC came off as well. I thought I could see "A23", but no guarantee, and it isn't much to go by :(
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #30 on: October 08, 2024, 07:05:25 pm »
Don't worry.
Play with the light direction. Wet the surface. Take some photos but only with a tripod.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #31 on: October 08, 2024, 07:24:20 pm »
I tried to be carefuly, but it didn't work. The number came off with the plastic. It's gone. I'm so sorry! :(
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #32 on: October 08, 2024, 07:47:17 pm »
Ring the chip legs. Find Vcc, Gnd, Drive and CS numbers.
Try to clean with hot iron.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #33 on: October 08, 2024, 07:49:25 pm »
Yes, I can access the legs, it wasn't difficult to get the material off the legs.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #34 on: October 08, 2024, 09:32:19 pm »
It turns out that vcc, drive and gnd are all shorted out.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #35 on: October 09, 2024, 08:20:24 am »
Drill out the center of the chip with the crystal.
Check all the pins for short.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #36 on: October 09, 2024, 09:00:37 am »
Ok, done. The short is gone.
Here are the chip connections (see picture):
Chip pin 1 - contact 2
Chip pin 2 - contact 1
Chip pin 3 & 4 not connected
Chip pin 5 - contact 3
Chip pin 6 - contact 4
Chip pin 7 - contact 5
Chip pin 8 - contact 6 & 7
 

Offline pienari

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Re: Help with dead AT PC Power Supply
« Reply #37 on: October 09, 2024, 09:02:09 am »
Is that dip8 just pwm controller?
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #38 on: October 09, 2024, 10:22:14 am »
Please see PWM controller pinout.


Double check Current Sense pin.

Clean pins 4, 5, 6 of optocoupler and ring the connection as well.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #39 on: October 09, 2024, 10:48:49 am »
I drawn lines in to the picture where the pins of the PWM connect to.

Is the opto coupler the chip next to the PWM? Are those the right pin numbers?
Where are the pins supposed to connect to?
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #40 on: October 09, 2024, 11:16:00 am »
Please see the corrected picture
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #41 on: October 09, 2024, 11:26:13 am »
Measure C10 capacitor
Use the drawing below to understand the possible connection.
« Last Edit: October 09, 2024, 11:27:49 am by Harry_22 »
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #42 on: October 09, 2024, 12:36:50 pm »
Pin 4 of the opto coupler is connected to pin 6/7 on the board (pin 8 of the PWM).
Pin 4 and 6 do not connect to the PWM or the board.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #43 on: October 09, 2024, 01:02:14 pm »
Ring optocoupler pins 4,5,6 in diode mode, assuming that this is NPN transistor.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #44 on: October 09, 2024, 03:28:58 pm »
I didn't know which pins to treat as B, C and E, so I just took some measurements:
Red probe on 6: 0.61V between 6-5 and 6-4. OL when black on 6.
Red on 5: OL between 4 and 6. Black on 5: 0.61V between 5 and 6, OL between 5 and 4
Red on 4: OL between 5 and 6. Black on 6: OL between 4 and 5, 0.61 between 6.

I hope that's useful.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #45 on: October 09, 2024, 04:22:42 pm »
Good.
Please measure resistance between pins 8 and 4 of PWM.

Double check that pin 8 PWM is connected to pin 4 of optocoupler.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #46 on: October 09, 2024, 07:55:19 pm »
The resistance between pin 4 and 8 on the PWM is 12k Ohm.
There really is no continuity between PWM pin 8 and optocoupler pin 4.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #47 on: October 09, 2024, 08:29:05 pm »
Pin 4 of the opto coupler is connected to pin 6/7 on the board (pin 8 of the PWM).
There really is no continuity between PWM pin 8 and optocoupler pin 4.
What pin of opto coupler is connected to pin 8 of PWM?

Please send a photo with ะก10 marking.
 

Offline naujoksTopic starter

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Re: Help with dead AT PC Power Supply
« Reply #48 on: October 09, 2024, 09:43:10 pm »
Pin 8 of the PWM is connected to pin 5 of the optocoupler.
 

Offline Harry_22

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Re: Help with dead AT PC Power Supply
« Reply #49 on: October 10, 2024, 08:32:46 am »
Pin 8 of the PWM is connected to pin 5 of the optocoupler.

Much better!
Please measure the capacitance of C10.
 


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