Zalman TNN300 Power Supply

[nolon2020]

Hi Forum

I am having a hard time fixing my Zalman Power Supply. Maybe somebody can
help me, what I have done so far:

measured DC on the main CAP => 320V DC

5Vsb Standby Voltage is too low => 3.3V

so the psu will not start, but what can be the reason for the low standby Voltage. I have tested the diode and the capacitor on the secondary side, and they are ok. So I have no idea how to proceed from here.

Any suggestions are welcome

[selldoor]

Re: Zalman TNN300 Power Supply

Can you post good clear close up pictures of it. PC psus are a mystery to me but many are similar inside so someone might recognise it and suggest where the problem might lie.
Use manage attachments JPGs less than 3mb load ok

[nolon2020]

Re: Zalman TNN300 Power Supply

Here you go
I could not really identify the chips on the riser pcbs

Weltrend
WT7517 is the DIL-16 which is not getting enough poweer.

[selldoor]

Re: Zalman TNN300 Power Supply

Well Id say the PFC chip on the riser has blown it looks burnt and it appears to have impacted on the smd components below.
You could try gently cleaning the surface of the chip with IPA to try and find a few more letters.
I think when the PSU is on if the PFC was working the volatge on the BIG cap would go up to 380-390 so that suggests it is not working.

[nolon2020]

Re: Zalman TNN300 Power Supply

Ah sorry the picture of the riser is a bit misleading because of glue residue, I hope I can get the same psu from a friend which is in better condition so I can compare the two and find the problem. But I can get it only by next weekend, thank you for your help up to now I will report my progress next weekend.

Cheers

[nolon2020]

Re: Zalman TNN300 Power Supply

I could get another psu of the same build, and I am 100% positive that there is an issue with the 5Vsb but I am none the wiser what really the problem is. I saw the Bestec 5Vsb circuit and I would say the circuit looks a lot like the TFX0250D5W everell posted. However I am not able to get it to run again for the heck of it. So I have the primary +320 V but the output is simply too low.
So I am still as clueless as last weekend.

Any ideas ?

Thanks

[selldoor]

Re: Zalman TNN300 Power Supply

As it has PFC the voltage on the main caps should be higher than 320vdc - Have you had any luck getting the part numbers?

[everell]

Re: Zalman TNN300 Power Supply

The TNY268 is the 5vsb chip. Looks like zener diode ZD3 may have been a little hot as the pc board looks slightly discolored.

You must get the 5vsb working properly before the rest of the circuitry will work. The feedback winding on the 5vsb transformer provides power to the TNY chip. The feedback DC voltage sometimes also provides power to the PFC chip. Measure the Vcc voltage powering the TNY chip. To determine which pin is Vcc you can download a data sheet from Digikey. Let us know what Vcc voltage you find on the TNY chip.