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mikey5791
Badcaps Veteran
Last Activity: 03-17-2025, 10:56 PM
Joined: 12-19-2014
Location: Sabah
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Hi momaka,
    As per your comment on post #16,

    "To do that, remove the dummy load resistors and test each rail's resistance to ground as well as to each other... and make sure to leave your meter connected for a few second so that the readings stabilise - that should make it clearer to see what is going on.)"
    Fyi, i removed all the 3 dummy load resistors 15ohm, 51 ohm and 270 ohm for all the 3 rails. The resistance test on 2k scale are as follows:
    3.3v to ground="1"(this means infinite on my dmm)
    5v to ground="1"
    12v to ground=1.932k...
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Sorry for late reply. Got some matters to attend lately.

    Yes, my previous readings are in kilo ohm range.
    Fyi, i did the voltage injection where i injected all 3.3v, 5v, and 12v simultaneously from a good psu.
    The bad psu shows purple line standby votage of 4.54v and grey PG line of 5.26v. Then i removed the orange 3.3v line, the bad psu grey PG line goes up to 5.53v.
    Next i removed the red 5v line, the bad psu grey PG line drops to 0.26v. May i know what all these tests are for? Is it saying there is still an issue at 5v line ? Kindly advice and guide if i need...
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Btw, am i doing the voltage injection test correctly as per my post no.14? Or i need to inject all the three rails namely 3.3v, 5v, and 12v simultaneously...
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  • mikey5791
    replied to Help needed to revive a blown power supply
    in Troubleshooting Power Supplies and Power Supply Design
    As per your recommendation, i replaced R6 with a 2.2k ohm resistor. Those diodes 1n4148 connected to base of 13007bjt are tested good with one leg desoldered off board . Also both the 1 ohm resistors are good within spec as well.
    In addition , the TO-92 transistor near the middle transformer are the c945 type. Off board, they tested good.
    Upon power on ac with series light bulb still connected in place of the fuse. The light bulb lights a second then off, but there is still no dc voltage output on any rail. I wonder what other component could be the cause of no power, with 5v standby...
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Fyi, i did checking for short circuit between the various rails by setting my dmm to 2k resistance mode. Here are the results:
    3.3V to 5V is 0.039 ohm
    3.3V to 12V is 0.163 ohm
    3.3V to -12V is 0.508 ohm
    5V to 12V is 0.186 ohm
    5V to -12V is 0.531 ohm
    12V to -12V is 0.655 ohm
    (For info, this psu does not have -5V rail)

    In addition, i tried the voltage injection method as suggested. I connect Ground wire of a good psu to ground of the bad psu. My red dmm(on 10A socket) to 3.3v rail of good psu while my black dmm to 3.3v rail of the bad psu, while...
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    Last edited by mikey5791; 02-26-2025, 04:09 AM.

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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Fyi, i attached two old ide hard drives as load for testing but the psu fan remains still and there is no dc output ....
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    On secondary side, the dummy resistor at 5v rail is green,brown,black,gold(51 ohm) while at 12v rail is red,violet,brown,gold(270 ohm) and at 3.3v rail is brown,green,black,gold(15 ohm).
    Did resistance test to ground, at red wire 5v rail resistance is 48 ohm while at yellow wire 12v rail resistance is 157 ohm and at orange wire 3.3v rail resistance is 10 ohm.
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  • mikey5791
    replied to Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design
    Before power on ac, i connect the psu power cable to a series bulb limiter and the bulb lights a second then complete lights off.
    Is this confirming there is no shorts inside the psu or do i need further test to confirm the output diodes for shorts? Kindly advise. Thanks for the tip.
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  • mikey5791
    started a topic Tiny Tech ATX480W output power ticking
    in Troubleshooting Power Supplies and Power Supply Design

    Tiny Tech ATX480W output power ticking

    Hi to all forum members,

    ​​​​​​This psu (Tiny Tech model ATX 480W) had been installed in a very old Windows XP PC but recently i pulled it out as the pc cannot start. To test it, i jumped the green wire and black wire on the 24 pin connector. The psu fan jerk a bit but not spinning. I used my dmm to check dc voltage on output connector wire, the 5v red wire keeps ticking a bit at around dc1v....then drops and ticking again around 1v. It is the same situation with the 12v yellow wire.

    Fyi, i desoldered the secondary side electrolytic cap those over 1000uf...
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  • mikey5791
    replied to Help needed to revive a blown power supply
    in Troubleshooting Power Supplies and Power Supply Design
    Thank you for informing.
    Fyi, i did a rough test on TL431 using input of dc 6v from dry batteries pack assuming the TL431 will switch on the red led upon reaching reference voltage of 2.5v. I had attached image of the test circuit and the breadboard with lighted led. Does this test confirm the pulled TL431 is still good?

    Appreciate if anyone can correct me if my test method is not proper and kindly suggest if i can use a digital multimeter for further test....
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  • mikey5791
    replied to Help needed to revive a blown power supply
    in Troubleshooting Power Supplies and Power Supply Design
    Hi to all forum members,

    Found some free time to go back to this old post. Upon tips from momaka, i desoldered few of the driver transistors near the PG(power good) area. At Q5 is TL431, Q7 is STC945(npn) Q8 is STA733 while at area near the opto isolator is TL431. Apparently after testing by dmm diode test, i found both the trans TL431 are faulty.
    Since TL431 is pnp type, on dmm diode test i place black probe on base, while red probe on collector, then on emitter. The red probe showed some reading meaning it is good. But when i place black probe on emitter, then red probe...
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  • mikey5791
    replied to Need help to replace burned resistor in 350w atx psu
    in Troubleshooting Power Supplies and Power Supply Design
    Hi all forum members,

    Yesterday i changed both the resistors to 4.7k ohm(color yellow, violet,red, gold) at the burned area and voila. The PG (power good) detected 5vdc, yellow rail got 12vdc, red rail 5vdc, orange rail 3.3vdc.
    Fyi, i let it power on for 10 minutes, no smoke or any spark. Seems it is in working condition, but i will likely use it for some small electronic project .

    Thank you to all who helped to revive this cheap psu. At least one less item goes to the salvage dump.
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  • mikey5791
    replied to Need help to replace burned resistor in 350w atx psu
    in Troubleshooting Power Supplies and Power Supply Design
    Thank you for all your replies. In my stock i seemed to have resistor value of 1k, 2.2k and 4.7k. Will it be ok if i changed both resistors(currently 200 ohm) to 4.7k to be on the safe side and expect the psu to run.
    Kindly correct me if i am wrong....
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  • mikey5791
    started a topic Need help to replace burned resistor in 350w atx psu
    in Troubleshooting Power Supplies and Power Supply Design

    Need help to replace burned resistor in 350w atx psu

    Hi to all forum members,

    Got this faulty 350 watt atx psu dirt cheap from a local online seller as i am keen to use it as a learning tool to repair faulty power supply.
    The faulty part is quite obvious from the burn area near the 16pin KA7500 BD pwm. The fuse is still intact with good continuity.

    Upon power on ac, there is 5vdc standby power on cathode of diode D14 and about 10vdc on cathode of diode D13.(This should be the aux power to generate the 12v and 5v rail.)
    Initially i replace the two burned resistors near my marked red arrow to 200 ohm resistor...
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    For your info, the 5V is not present at the 5V test point at TCON board. From the power board at the output pins CN902 and doing dc voltage test, i got 5.50v from pins 8,9,10 (+5V). In addition, i got about 30v from pin 4(+15V). I also did voltage test at caps C908 and C907 and the positive side i got 31vdc. Not sure if these readings are normal.

    From the main board while doing the voltage test, i got 3.47vdc from pins 5,6,7. The caps at c710 reads 1.88vdc, c702 reads 3.48vdc while both c705&c716 reads 5.51vdc. I found one cap at c433 with zero volt , no voltage whatsoever. It...
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    Yes, it is 786 ohms on continuity reading. That means there is resistance. If the reading is "0" zero on my digital multimeter it means complete continuity.,no resistance whatsoever.
    I will try to trace why the 5v is missing from TCON board.
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    By DMM set to continuity mode, TCON board connector disconnected from main board, my black probe on pin 4 ground while red probe on VIN test point, i got reading of 786. If i put my DMM black probe on the furthest right side ground copper plane near the brown sticker, i got reading of 623.

    By the way, where else can i check for possible short? Kindly assist.
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    Based on your reply, my understanding is the 5v pin should be last five pins on the right side of the connector. By DMM resistance test set to 2k scale, black probe on ground near CN1 and red probe on the 5v pin(as mentioned up here), i got "1" infinite reading. I attached an image of my 5v pin test point as shown by tip of a ball pen. Correct me if i am wrong.
    To your question earlier, the TCON was attached to main board.
    Fyi, on the right side of connector there is a white color component with "I" marking which i think is a fuse. It has continuity. There is also...
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    From my DMM resistance set to 2K, red probe on the 5V pin and black probe on ground near CN1 pin on the LVDS connector i got resistance of 0.268

    The sticker on display panel says LM185WH2 (T2)(BB) from L&T Display but i couldn't find any info from Panelook.com

    Attached image of the LVDS connector....
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  • mikey5791
    replied to Philips 196V3L monitor power led off
    in Troubleshooting Computer Displays
    Fyi, the monitor does not display any image if i connect the flex ribbon cable and the power led indicator does not light up or turn on. That is the reason i suspect somewhere is shorted as the power led indicator on the front side is not lighted.
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