Weirdest power problem

[DjKrish]

Yes, this is the weirdest ive ever seen. Taken from a CD player. Just nice and compact with not much components.

First it has no power. Dismantled the unit, unplugged everything and tested the power supply on its own. While the power plugged, hearing a ticking sound on the switching transformer. Tested the port for 12V, only 5V was showing.

OK, i replaced all the electrolytic caps and ceramic caps, NO GO
Swapped the N channel transistor. Still NO GO
Soldered all the joints, NO GO
Tested all the normal diodes and SMD diodes, all gives good reading, none shot

But the thing is, all of a sudden after switched off for sometime and switch on the unit again, it will work providing solid 12V and there wont be any ticking sound and the entire set works fine . Then when you switch it off and switch on again after a while, the ticking sound will start doesn't matter with load or without load. Anyone had this issue before?

All other boards on the player is fine, the power supply is faulty on its own as it gives the ticking sound without anything plugged in to other boards.

[budm]

Re: Weirdest power problem

Did you check or replace startup/running cap C11 in the HOT side?
The ticking sound you hear is due to SMPS is in start-up shut down mode whcih can be due to bad caps or bad rectifier in the cold side.
BTW, the schematic looks to have error, C5 is labeled as 330/25V, that cannot be right, that is the main filter cap so it cannot be rated at 25V, C11 is shown as 22/5V which is wrong also. See what the real rating of the caps are on the board and compare them to the schematic.
https://www.badcaps.net/forum/attach...3&d=1519382548
The board is fed by 120VAC or 220VAC?

[eccerr0r]

Re: Weirdest power problem

I was about to guess C11 but because "all" caps were replaced it couldn't be...
I think this is C11:

[budm]

Re: Weirdest power problem

Looking at the bottom side of the board it does not look like there is sign of soldering works on the cap's legs.

[DjKrish]

Re: Weirdest power problem

Looking at the bottom side of the board it does not look like there is sign of soldering works on the cap's legs.

Thats because after soldering everything, to make sure its clean i cleaned the entire board with alcohol and toothbrush

[budm]

Re: Weirdest power problem

OK, thanks for the clarification.
So some how it is stuck in the ON/OFF cycle.
Have to look for the spec sheet of that SMPS IC to see what other condition will cause the IC to get stuck in that mode.
SSC6210A IC is what is used on the board, correct?

[DjKrish]

Re: Weirdest power problem

OK, thanks for the clarification.
So some how it is stuck in the ON/OFF cycle.
Have to look for the spec sheet of that SMPS IC to see what other condition will cause the IC to get stuck in that mode.
SSC6210A IC is what is used on the board, correct?

Yes thats correct

[DjKrish]

Re: Weirdest power problem

I saw a tv power supply being repaired by a guy on youtube and it had the exact same problem. The transformer was ticking, he replaced optocoupler and walla its solved. At first he sprayed duster on the optocoupler to test it and yes upon spraying, the power worked fine and after it gets hot, the problem starts again.

https://www.youtube.com/watch?v=MGGyyi7gLO0

[DjKrish]

Re: Weirdest power problem

I have a optocoupler thats PS2571-1. Its very hard to find that particular part number but i believe we can use substitute right? Any reference i can get?

[DjKrish]

Re: Weirdest power problem

Update : Replaced the optocoupler, power supply is working fine now. No more ticking sound.

[DjKrish]

Re: Weirdest power problem

Replaced the optocoupler, power supply is working but the ticking comes back for few seconds like 10 seconds upon turning on if switched off for more than 10 minutes.

I think some smd ceramic caps needs checking.

[DjKrish]

Re: Weirdest power problem

Update : C6 smd cap shot. Replaced, so far so good.

[eccerr0r]

Re: Weirdest power problem

Thanks, I may have never checked the stays-cool optoisolator, never expected these to fail. I suspect that perhaps they're overdriven and hence fail.

Isn't C6 a MLCC, now these I wouldn't expect to fail unless they're physically damaged thus shorting...

[budm]

Re: Weirdest power problem

I wonder what that Thermistor TH3 is being used for, it looks to be for something to do with temperature. I did not have a chance to look up the spec sheet of the IC yet to see what pin 4 is used for.
So C6 has leakage resistance?
Keep an eye it to see if the problem comes back.

[DjKrish]

Re: Weirdest power problem

Thanks, I may have never checked the stays-cool optoisolator, never expected these to fail. I suspect that perhaps they're overdriven and hence fail.

Isn't C6 a MLCC, now these I wouldn't expect to fail unless they're physically damaged thus shorting...

Thats the worse part about smd caps

I wonder what that Thermistor TH3 is being used for, it looks to be for something to do with temperature. I did not have a chance to look up the spec sheet of the IC yet to see what pin 4 is used for.
So C6 has leakage resistance?
Keep an eye it to see if the problem comes back.

Yes sir. Was running for few hours, so far so good.

[momaka]

Re: Weirdest power problem

Isn't C6 a MLCC, now these I wouldn't expect to fail unless they're physically damaged thus shorting...

MLCCs fail "on their own" quite often, actually. It could be due to some light (or not so light) vibration or shock to the case, triggering a "sleeping" factory defect in the MLC cap. Or the damage could have been caused by improperly-calibrated pick-n-place SMD machine. I read an app note once that said that ceramic caps can develop internal cracks over time and short-out if the pick-and-place machine applied too much force or if the cap was subject to stress during PCB assembly. Also, if the ceramic cap is in a position where the board flexes a lot, that could also lead to internal fracture of the MLCC's layers and a short-circuit.

On that note, one of my neighbor's DVD/surround sound system appeared to fail all of a sudden after they moved to a new house. The unit would produce lots of sparks during turn On every time it was plugged it. The cause was a short ceramic cap on the output of the SMPS, which likely cracked when the DVD/surround system was moved. The sparks happened every time because the SMPS would try to turn On, then detect a short-circuit, then turn Off again. I think my neighbor donated it after I fixed it, as she didn't trust it anymore, lol. But that was really the whole problem. Unit worked flawless after I removed the faulty ceramic cap and replaced it.

So yeah, these small ceramic caps can cause lots of issues. Never ignore ceramic caps!

[Dan81]

Re: Weirdest power problem

On that note, one of my neighbor's DVD/surround sound system appeared to fail all of a sudden after they moved to a new house. The unit would produce lots of sparks during turn On every time it was plugged it. The cause was a short ceramic cap on the output of the SMPS, which likely cracked when the DVD/surround system was moved. The sparks happened every time because the SMPS would try to turn On, then detect a short-circuit, then turn Off again. I think my neighbor donated it after I fixed it, as she didn't trust it anymore, lol. But that was really the whole problem. Unit worked flawless after I removed the faulty ceramic cap and replaced it.

So yeah, these small ceramic caps can cause lots of issues. Never ignore ceramic caps!

I had the same happen with an TV

It had a bad ceramic cap inside (burnt to ashes, rest of components weren't broken or anything, just that cap) and wouldn't turn on because of it. I removed it (didn't bother with a replacement, it was a very narrow space) and tested the TV. It turned on and worked perfectly just like it does now.