Why this Primary Section is not trunning on ??

[Galib]

I have added the diagram . The primary section is just similar like the diagram . There used MJE13007 instead of 2SC2625 . In the primary section Pair of MJE13007 is not turning on and they are not creating AC . Although all parts in the Primary section are good . But still it is not creating AC !! What is the problem still there ?? What is preventing primary section to stop creating AC ?? Please help ............


Galib

[c_hegge]

The problem could be with the drive circuit, which is circled in the schematic. Test the components there.

[Galib]

Nope !!! When I am switching then IC TL494 Output 8 and 11 pin going Low (From 3V to 1.5V) and Driver Transformer pins are going high (From 1.5V to 3V) . That means- the Driver section working properly . May be the problem is in the Primary high voltage section . But what is that ?? Every parts in primary is OK !!! It is not giving continous AC Pulse to Main Transformer . It is similar kind of problem of CFL bulb circuit where AC signal is not present continously !!!

Have you faced such kind of problem in Primary High voltage section before ??

[c_hegge]

Well, then, the problem is unlikely to be with the drive section or the controller IC. When you say that the primary side parts are OK, do you mean -all- components (including all of the very small ones), or have you only tested the main components? The problem seems like it is in the primary section, such as an open diode or resistor.

[Galib]

Look at the primary Section - There are two Transistors and few components to loop both transistors giving continuous AC Signal . To check these few components you do not need more than 15 minutes . Firstly - I suspected two Start-up capacitors and I changed them also but it did not work . ATX PSU is such kind of SMPS where component's "Full Operating System Failure" problem occurs eventually !! I think such kind of Full Operating System failure raising there . I have decided - I will change all the components of primary section today , even Transformer also . Let's see - what happens !! If it is turns back then good, otherwise I will throw it .

- Thanks
Galib

[c_hegge]

I know it's not that hard to test them if you have the right tools, bit I've heard others say they've tested the components, but have really only tested the main components. I just wanted to make sure that wasn't the case here. Re-building the whole primary section isn't a bad idea if you have to get it going, and it would completely rule out that that area of the PSU.

[Galib]

Yup !!! I have done it . The PSU is running fine now . The "Full Operating system Failure" problem was of the Main Transformer . It was refusing to work in full operating mode !!! Why transformer behave like this ?? What happens inside transformer ?? But Transformer showing perfect with multi-meter !!! This is the third time I have faced problem with transformer . Previous two were faced with +5VSB Transformer Failure . But every time Transformer shows OK with meter !!! Strange to me ...... !!!

Thanks
Galib

[c_hegge]

The transformer probably had shorted windings. Generally, it happens when the transformer is too small for the job, or the power supply runs too hot. You're lucky it didn't blow up the switching transistors, though. Overloaded transformers often do that.

[Galib]

Of course Primary Section was damaged . It's both switching transistors MJE13007, two 2.2 ohm and two Crystal diode were blown . After Replacing them, The primary section was not turning on - that was the problem .

[c_hegge]

Ah. I didn't realise they were replaced. Since you didn't mention that, I thought the parts in there were all the originals.