Ticking PSU

[madan1]

Hi everyone.
Can anyone help with a PSU which is making a ticking noise. The noise gets louder when load is applied ( it is still audible even with no load ).
The PSU is UOP325D-0512-A ( still have not found schematics ) and looks like the attached images.
I desoldered and measured all 6 electr. caps and 5 of them were fine. The faulty one was the green one ( right next to the 2 big ones on the low V side ).
Any ideas what could be causing the ticking?

[R_J]

Re: Ticking PSU

The ticking is caused by the primary trying to start but can't usually caused by a short in the secondary somewhere.

[madan1]

Re: Ticking PSU

Well the PSU starts fine every time and produces both 5V and 12V.
I haven't noticed any excessive heat or smell.. what will be the best way to look for short without desoldering and checking each individual component?

[R_J]

Re: Ticking PSU

I thought it was not working, if the 5v and 12v are there then there is no short. The pictures are too small to really see anything.
The ticking without a load could be normal, Was it working before you changed the cap?

[madan1]

Re: Ticking PSU

Yes, it was working before I changed the cap.
Here are some better photos.

[petehall347]

Re: Ticking PSU

looks like the board needs a good clean and the dry joints attended to with fresh solder

[madan1]

Re: Ticking PSU

All joints resoldered/reheated and the pcb cleaned.
Still got the same "ticking" and output ripple.
Here is a recording of the ticking and what I have on the output. Is this ripple acceptable?

[R_J]

Re: Ticking PSU

I have no idea where that ripple is coming from but at 49Hz it must be from the primary, That power supply operates at about 30-50 Khz. So it could be that the main filter cap is bad, sometimes those large caps can't be checked properly with a meter, And it does look a little bit domed but hard to tell from the pictures.
I cant play m4a

[madan1]

Re: Ticking PSU

Here is the audio converted to mp3.

I desoldered and measured the big cap on the main side and it was within 10% of its original capacitance. Anyway, I will switch it with another one and test it again.

[madan1]

Re: Ticking PSU

Alright, I think I found the problem.
I swapped the 47uF/400V cap with a 100uF/400 ( that's the only 400v which I have at the moment ) and the noise disappeared.
Also the ripples changed ( see attached ).
I tried to measure again the 47uF/400V but couldn't get a good reading this time. It looks like there is some kind of an internal failure.. probably one of legs is not getting good contact with its conductive plate.

So I guess the "ticking" issue has been resolved ( kudos to R_J ).
Do you think there is any point in continuing working on this to get better outputs?

[budm]

Re: Ticking PSU

I am curious as to where you hook up up the scope too to get that 50Hz (20mS) reading, the primary side use full wave rectifier so the ripple on the main cap will be 100Hz.

[madan1]

Re: Ticking PSU

I used the black output wires for ground. The orange wire is +12V, the red - +5V

[budm]

Re: Ticking PSU

I am curious, If you do not have the power supply connected to the AC outlet, what do you see on the scope (leave the probes hooked up the same way)?

[madan1]

Re: Ticking PSU

I am curious, If you do not have the power supply connected to the AC outlet, what do you see on the scope (leave the probes hooked up the same way)?

There you go.
Leads hooked to the same wires ( black and orange ), no AC.

[stj]

Re: Ticking PSU

leaky diode in the primary rectifier maybe??
also, connect the supply negative input to mains, but not the live wire - see if you get the 50Hz

[R_J]

Re: Ticking PSU

Are those waveforms in post #10 with a load on the power supply or without a load?

[budm]

Re: Ticking PSU

I just look at the board and I can see X cap (blue disk cap in black shrink tubing) connected between hot side and the GND cold side so I believe that is the reason for seeing the 50Hz.

[momaka]

Re: Ticking PSU

Faint ticking without any load is normal for some discontinuous flyback power adapters, but not all of them, and certainly not with a load. So most likely that failed primary cap was the issue. Other times, this can happen if the small "start-up" cap on the primary fails... though I don't see one on your power adapter. So that and the lack of an PWM controller tells me this is likely a 2-transistor self-oscillating design with feedback. And for this design, ticking is not normal.

I desoldered and measured all 6 electr. caps and 5 of them were fine. The faulty one was the green one ( right next to the 2 big ones on the low V side ).

I see the blue caps are Ltec brand. In my experience, these are very unreliable caps. They seem to go bad quite often in Delta, HiPro, and Lite-ON ATX PSUs. In fact, I just posted a thread about one of these PSUs two weeks ago, showing how badly these caps can fail without any visual signs at all:

Therefore, I suggest you to not trust these Ltec caps and replace them preemptively (especially if doing this for a customer - high chances it will come back within a year or two down the road).

I just look at the board and I can see X cap (blue disk cap in black shrink tubing) connected between hot side and the GND cold side so I believe that is the reason for seeing the 50Hz.

This.

It's actually a Y2-rated cap between secondary-side ground and primary-side negative (-) bus (i.e. connected to the negative lead of the big input cap.) I believe this is done for attenuating EMI/RFI to and from the PSU.

[budm]

Re: Ticking PSU

"It's actually a Y2-rated cap between secondary-side ground and primary-side negative (-) bus (i.e. connected to the negative lead of the big input cap.) I believe this is done for attenuating EMI/RFI to and from the PSU." That is correct, I use X/Y rated cap for that purpose to pass EMI compliance testing, but since one side is connected to primary GND circuit (not safety GND), that means the cold side circuit GND which will have some AC current flows dues to Xc at 50Hz (small level) through scope safety GND, thus the 50Hz showing on the scope.
It sure does look like -2Transistor SMPS setup.
BTW, if op measure the AC Voltage between cold side GND and the safety GND, he will see AC Voltage present.

[madan1]

Re: Ticking PSU

Are those waveforms in post #10 with a load on the power supply or without a load?

The photos are without load, but I'm able to trace the ripples down to the connected pcb.

I see the blue caps are Ltec brand. In my experience, these are very unreliable caps. They seem to go bad quite often in Delta, HiPro, and Lite-ON ATX PSUs. In fact, I just posted a thread about one of these PSUs two weeks ago, showing how badly these caps can fail without any visual signs at all:

Therefore, I suggest you to not trust these Ltec caps and replace them preemptively (especially if doing this for a customer - high chances it will come back within a year or two down the road).

All caps were measured out of the board and only one was found with 30-40% lower capacity.. and of course the 47/400 one which seems the have internal failure not related to its capacity.
The board is for a NAS which I'm going to use at home, so it is not a problem to keep an eye on the PSU and its caps




Unfortunately, I "killed" the PSU by discharging the 100/400 cap with a srewdriver.. most likely the arc jumped to something else and now I do not see anything on the low-V side.
Here is what I was able to draw as a schematic for the hi-V side ( see attached, the rectifier part is skipped ).
The bad components which I found are ZD103 and C107. I was not able to find the same design, but in others they show it as "17-18V"(?). Also, ZD102 on the board is labeled as "ZD", but the actual component is detected just as a diode.
The big transistor is K3567, the small one - C945

At this moment I 'm starting to think that it would be better just to get one of those https://www.aliexpress.com/item/12V1...310683501.html instead of fixing it.