Help for fixing PSU

[hkqq2010]

Re: Help for fixing PSU

Normally When Primary 5VSB section is Designed with Transistor (Like C5027, C3866), I found T3 Transformer is 4 ohms . But in Mosfet based Design Transformer's I found 3 ohms Resistance . No Problem with 4 ohms if your Series Bulb 40W does not glow . Higher Rated of C502 or C503 will increase your output voltage . I am not sure about the particular capacitor . Most probably it will be C502 . Increase it littlebit (Like 222 PF) and measure the output voltage, what happens .

Thanks for your patience and useful info. But I have no 222pf cap on hand. I need to get one with the 18V zener soon.

Yes, I am sure about that - It is 18V . 18V is available in the market . And do not remove the 33K Resistor . Use the 18V Zener in Parallel with 33K Resistor . You can use 16V, But not 20V .

I see ... thanks for useful info.

Replace it with previous Regulator with which was given you 5V .

I had already mixed with other AZ431, and can't identify it now.

yes, If the Circuits are from different company, then Output "5VSB, GND and IC supply" will be in different places . You Just need 1 Yards wire to check it with another transformer . Cut the 1 Yards wire into 7 Pieces and connect those 7 pieces wires with circuit and Transformer according to your need and keep the transformer besides the circuit board .

Thanks for your suggestion, but I get one good PSU from my friend which has the same EE-19. I used it to test all my 3 EE-19, they are all good with no single sound and keep +5Vsb at +5.0V.
Besides, I had tested all my AZ431, C945 amd Optocoupler with the good PSU, they are all good.

That makes me REALLY want to know which component make that terrible
hissss sound and drop down the +5Vsb.

"I will catch you eventually, wait for me .... "

Ya, Gate Voltage 4.x is OK . Because Gate voltage is upto +/- 20V for 2N60 .

I see. Thanks for your great info, caused that good PSU does not use MOSFET.

Set the Multimeter to AC 1000V . Now look at the circuit - Transformer's One pin is connected with Mosfet's Drain Pin directly . Now with Just any ONE probe of Multimeter's touch that line and measure how much AC voltage is present there ?

My multimeter is digital and auto-range. Anyway, I set it to AC V, and use ONE probe to touch the Drain, it shows only 1.4x.

Finally, thanks for your help, but I will be off in next 2 days. Many thanks in advance.

[hkqq2010]

Re: Help for fixing PSU

You should do the SMPS IC mod.

I.E. using the FSDM311, or TNY377

It will be easier than fixing this circuit and this circuit you are trying to fix is not reliable - if something goes wrong the output voltage can go over 20v! (Not with a proper control chip!)

Yes, with IC mod, it is better.

Recently, I fix another PSU, Bestec ATX300P5WB, which used TNY276PN for its +5Bsb. Thanks for "everell " who provide me the similar circuit, I can easily found out TNY276PN was defective.

[Escort Eagle]

Re: Help for fixing PSU

That makes me REALLY want to know which component make that terrible
hissss sound and drop down the +5Vsb.

Is every Transformer is hissing with that Faulty Circuit ??

[hkqq2010]

Re: Help for fixing PSU

Sorry for late reply .... I am too busy ....

Is every Transformer is hissing with that Faulty Circuit ??

Yes, 2 is smaller, and the other is louder. now I use the louder one.

Besides, because of my interest, my friend give me another PSU with hisssss sound coming from the main o/p which he give up to fix it.

I will get the 222pF cap and 18V Zener from the shop ... maybe today.

Furthermore, I will go to see if I can get an 2nd-hand PSU but useful from the shop with the same model of my PSU and my friend's PSU, so that maybe I can fix them by replacing component by component to see which causing the hisssss ....

Finally, I may borrow an oscilloscope to have thorough check-up .....

[hkqq2010]

Re: Help for fixing PSU

.... because of my interest, my friend give me another PSU with hisssss sound coming from the main o/p which he give up to fix it.

My friend gave me a very old PSU, G-tech (P) Model: LC-B350ATX, which even have no ATX12V 4Pins connector. He had replaced all the power transistors for main outputs and +5Vsb. +5Vsb is back. While shorting green wire to ground, it has main o/p but with hisssssss sound, furthermore, the main o/p is vanished when loading with an DVDRom. He give up and give it to me.

I further study it. I found the diodes and resistors connected to the two pull-push power transistors of the main supply is damaged. After replacing them, it can load with an DVDRom, but still with hisssss sound.

Then I replaced the main transformer, the hisssss sound becomes smaller. Finally, I decided to replace the 2.2µ cap connected to those defective diodes and resistors. I though that the components of that path may all be damaged. ie, 2 power transistors, 2 diodes, 2 resistors and main transformer are all damaged. Miraclely, the hisss sound is disappeared.
, , , , , , , , , , , ,
Then I replaced back the main transformer, the hisssss sound come back again. It proves the main transformer is really damaged. Then I dissambly it, but, bizarrely, I can't find any defect visually.

bizaree .... bizaree .... bizaree ....

Anyway, I had finally fix it. I hope it may give me some hints to tackle the PSU which hisssss sound in +5Vsb circuit.

Thanks for all.