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Old 08-10-2019, 06:14 PM   #1
SoporteHR
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Default Help please, Line + 5VSB increases the voltage.

Help please, Line + 5VSB increases the voltage.

Hello everyone, receive a cordial greeting.

I have an ATX 500W power source. Chassis Model: LPJ2-23.

It turns out that when measuring the line voltage + 5VSB. After the source is turned on, the voltage gradually increases until it reaches approximately 7.8 vdc.

If I leave it connected to the power but turned off, the voltage remains stable at 5.1vdc. approximate

I thought I was a capacitor in that sector. Then I measured them with the ESR Raptor and they measured me well, but since I don't have a capacitor to know the real capacity, then I proceeded to replace the larger capacitor of 1000uf x 10vdc. I tried and same behavior, the voltage slowly rises to reach 7.8vdc.

I proceeded to replace each capacitor involved in that line one by one and was testing the same result.

Last instance, replace TL431, same case, replace ceramic capacitor 104, same case.

I demolished the 1.5kohm resistors and measured them, and they are very valuable. both.

When the source starts for the first time, the voltage at the transformer diode output of the VSB line starts at 12vdc, by the time the output voltage rises to 7.8vdc, the output voltage of the diode approaches 17
volts

I don't know what else to try. Please if anyone has an idea, I appreciate it in advance.

The controller of this source is the WT7514L

Disassemble the source as a custom to check them when I get a computer from a client, in this case I had originally damaged the output capacitor of the line + 5vdc. Replace it arm the source, install it on the computer and the PC worked perfectly, until I turned it off and wanted to turn it on again, at that time the power source turned on and off immediately. I tested the PC with another power source and it works perfectly.

Thank you very much in advance.
Attached Images
File Type: jpg All Caps Change P1250277.JPG (169.3 KB, 9 views)
File Type: jpg V 0.58vdc P1250270.JPG (181.4 KB, 9 views)
File Type: jpg Vin 12,7 vdcFirts Time P1250269.JPG (180.3 KB, 9 views)
File Type: jpg Vin 17vdc Past Time P1250271.JPG (179.5 KB, 9 views)
File Type: jpg VSB 5.1vdc P1250276.JPG (179.5 KB, 10 views)
File Type: jpg PSU OFF 32 Min Aprox P1250266.JPG (198.3 KB, 8 views)
File Type: jpg PSU ON Time 30 Min Aprox P1250264.JPG (183.1 KB, 7 views)
File Type: jpg Change VSB Volt 6.23P1250263.JPG (178.5 KB, 6 views)
File Type: jpg TL431 y Resitor P1250274.JPG (146.5 KB, 10 views)
File Type: jpg Change VSB Volt 7,4 P1250264.JPG (183.1 KB, 7 views)
Attached Files
File Type: pdf PSU ATX PWM Voltaje Controller lWT7514L V130 Datasheet.pdf (171.0 KB, 0 views)
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Old 08-13-2019, 12:28 AM   #2
Agent24
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Default Re: Help please, Line + 5VSB increases the voltage.

The WT7514L has nothing to do with the 5vSB. It only runs the main supply.

It looks to me like your 5vSB circuit is one of the 2-transistor designs. Are you sure the new capacitors you tried are good? With bad capacitors, the voltage regulation in these style of circuits is bad.

If you know the capacitors are good, then check the other parts in the 5vSB circuit. Optocoupler might be bad or something. Or a capacitor in the primary side.

The 5vSB is probably going to be quite similar to the one in this schematic.
Attached Images
File Type: jpg linkworld_lpj2-18_pc_power_supply_sch.pdf_1.jpg (270.8 KB, 6 views)
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Old 08-13-2019, 05:54 PM   #3
SoporteHR
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Default Re: Help please, Line + 5VSB increases the voltage.

Thank you very much friend.

I just checked the diagram and replaced the octocoupler, since on the primary side, my source has no electrolytic capacitor.

I am testing the source and it takes 2 hours without changing the voltage.

I suspect it was the octocoupler.

Now will you know what happened to the original octocoupler to generate that fault, leak in the internal transistor?

After the whole day the source was turned on, the voltage of + 5VSB remained stable at 5.11 vdc

Thanks for the help and excellent diagram.
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Old 08-14-2019, 01:32 AM   #4
stj
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Default Re: Help please, Line + 5VSB increases the voltage.

the led output slowly drops, philips tv's used to have a big problem with this because they put too much current into the led.
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Old 08-14-2019, 04:38 AM   #5
SoporteHR
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Default Re: Help please, Line + 5VSB increases the voltage.

Thanks STJ,

It sounds logical, the LED is degraded internally, but since replacing the optocoupler,
should I change the value of the LED resistance of this LED? To prevent damage to the new optocoupler.
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Old 08-14-2019, 05:16 AM   #6
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Default Re: Help please, Line + 5VSB increases the voltage.

no, that will throw off the output.
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Old 08-15-2019, 04:03 AM   #7
SoporteHR
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Smile Re: Help please, Line + 5VSB increases the voltage. - Resolved :-)

Thanks STJ. For the confirmation.

Yesterday I finished assembling the power source, to rule out and be sure that the fault was the octocoupler, I removed the new one and reinstalled the old one, effectively the voltage went back up to 6.8vdc.

Today 08-15-2019. The source continues to operate with the stable voltage at 5.17 vdc. approx. I left the equipment on all day yesterday. And it operated correctly.

I close the case.

Thanks again to everyone for the help. Have a great day.

Until next time.
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Old 08-15-2019, 06:05 PM   #8
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Default Re: Help please, Line + 5VSB increases the voltage.

Good to hear
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