Sanmim 12v Power Supply, Pulsing Output

[RukyCon]

Hello Again, I'm back with a small power supply that failed after a whopping 1500 hours of service (impressive, eh?). Now this repair isn't urgent as i do have a few extra units on hand, so i'm mostly doing this to work on my skills. Anyway, i've done a bit of probing around on the PCB, testing components, and have found nothing that seems to be out of the ordinary, but here are the components i've probed.
D2 (F7)
R5 (3.3Ω)
R6 (100K)
R4 (1.2Ω)
R11 (2K)
R18 (10K)
R19 (22Ω)
FS1
RT1
C1 (Aishi HS 15uf 400V)
C3 (Aishi WH 22uf 35V)

I've also probed the bootstrap winding of the transformer and compared that to a working unit, and they both matched. So i'm inclined to believe that there's something wrong with the driver IC. The part number on the IC appears to be 63L20, but after a lot of searching, i could not find anything about the IC.

So now what do i do? Did i miss anything? Any help will be appreciated.

[R_J]

The ic is a On-Bright OB2263, Check that the secondary/output diode is ok and not shorted, Check the dc voltage ACROSS C3 Post the voltage. It could also be a bad optocoupler.
Is the output voltage pulsing under load? Is it stable without load?

You can always buy another one for $1.93 + $2.03 shipping https://www.aliexpress.com/item/3281...archweb201603_

[petehall347]

i dont like the look of where the output cable is soldered .

[RukyCon]

Checked the diode, and it appears to be fine, i have not tested the C3 voltage yet as i need to replace the replacement power supply that replaced this one because get this, it just failed the exact same way as this one (it's the same brand & model as this one, just with way fewer hours (roughly 12 hours)).
Guess what power supply brand i won't be using in the future.

i dont like the look of where the output cable is soldered .

Don't worry about those, i checked them, and they are not shorted, however, i do agree that they look like crap.

[R_J]

What are you supplying with these? they are only a 1amp supply

[RukyCon]

Originally Posted by R_J

What are you supplying with these? they are only a 1amp supply

It's a small relay board that can only draw at most .6 amps.

And as i was testing the first supply to see what it's issue was, only to find that both PSUs were working fine on the bench, thats when i realized the issue i was running into might not have been due to a component fault, but due to the OCP kicking in before the supply is fully loaded, and it just so happens that the relay board's max current draw falls right on the line for the OCP, despite it not drawing enough current to warrant it. I still think there might have been something wrong with the first unit, as it did continue to pulse after disconnecting the load while replacing it, but due to the fact it's working fine now, it will be really hard to find the fault (assuming there even is one).

I'm really sorry about this, i did not mean to waste everyone's time.
I wish i could delete my account here to remind me not to ask these stupid questions.

[sam_sam_sam]

Originally Posted by RukyCon

I'm really sorry about this, i did not mean to waste everyone's time.
I wish i could delete my account here to remind me not to ask these stupid questions.

Please do NOT look at this way and here is why

I have had a few times in past working on something and when you bench test it seems to work ok ( but maybe not quite the way it should ) but then after I would reinstalling the device back in it might work for awhile then start doing the same fault again what the heck is wrong with this device

I once had it happened 3 or 4 times in a row and sometimes it something you just over looking or it is intermittent issues those are hardest issues to resolve

So hang in there

The most important thing to think about is someone might learn something from your experiencing working on this device because I can tell I have learned a lot of troubleshooting skills reading these posts and that is the main reason I am still reading post on this forum

I hope this helps

Data sheet in part

• Extended Burst Mode Operation
At zero load or light load condition, majority of the power dissipation in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the energy. OB2263 self adjusts the switching mode according to the loading condition. At from no load to light/medium load condition, the FB input drops below burst mode threshold level. Device enters Burst Mode control. The Gate drive output switches only when VDD voltage drops below a preset level and FB input is active to output an on state. Otherwise the gate drive remains at off state to minimize the switching loss and reduces the standby power consumption to the greatest extend. The frequency control also eliminates the audio noise at any loading conditions.

If it were me I would replace this chip ( and maybe even the mosfet as well ) because it might be having some kind of issues at minimum load ( and or look at this first for bad soldering joints around those areas ) or something that is intermittently shorting

[sam_sam_sam]

Bump

I do not use the quote format very often so when I am quoting something from another source like data sheet

So sometimes things do not quite go as planned

[R_J]

I'm really sorry about this, i did not mean to waste everyone's time.
I wish i could delete my account here to remind me not to ask these stupid questions.

Don't be sorry, it is not a waste of time. It could be that the supply is shutting down when the relay gets energized, Is the relay board near the power supply? if not, try adding a 1000µf/25v across the relay board 12 volt input. Due to the ic's load monitoring, it might not be the best choice for this application, but I'm sure ther is a way to make it work.

[RukyCon]

Sorry about my last comment, whenever things don't go to how i'd expect them to during a repair, i always suspect i did something wrong, since sometimes, that ends up being the case. I wish i did not say that, but stress got to me this time.

Anyway, i was doing some more testing on the supply and now i'm 99% certain the power supply(ies) are defective. But first, i should clear a few things up:

I thought something was wrong with the OCP of the PSU, turns out it might be fine, if kicking it at 1.5x the power supplies rated current is normal.

The relay board i was talking about actually draws closer to 300mA when all the relays are on.

• Extended Burst Mode Operation...

This could be the reason for this fault especially since it seems to start strobing if the board has been idle for a few hours with all the relays off (where the power draw is closer to 10mA), but, this is not the only relay board that uses this brand & model power supply, and as far as i know, the power supplies in those have not had the same faults.

Now this might be a stupid question, but should i try warming up the board while it's running? As i suspect something (the chip, or a diode) might be working fine at room temperature, but stop working when it warms up to a temperature it should still work at. I understand i might be wrong about this, so i'm asking just in case.

[sam_sam_sam]

Originally Posted by RukyCon

Now this might be a stupid question, but should i try warming up the board while it's running? As i suspect something (the chip, or a diode) might be working fine at room temperature, but stop working when it warms up to a temperature it should still work at. I understand i might be wrong about this, so i'm asking just in case.

No it is not

In fact that might be a good way to go about finding what might be wrong it

If you have a temperature controlled heat gun with a small diameter tube and can direct the air flow in a small area ( to one component at a time ) this would be the best way to do this also you can cool and area the same exact way

Use the lowest temperature setting to do this with the lowest air flow but not too low because of burning up the heating element

If I remember correctly mine temperature controlled heat gun the lowest temperature setting is 320* F if this is the case then do not put the tip too close to the components while you are doing this

[R_J]

You could try placing about a 100Ω 1/2w resistor across the 12v output, this should draw about 120ma and keep the power supply out of burst mode.

[RukyCon]

So the heating thing did nothing, i used a soldering heat gun set to 212F and aimed it mostly at the chip and diodes. So at this point i may just follow R_J's advice about adding a load resistor to try to keep the PSU out of burst mode (since it appears there might be no component faults), though for the last few days, none of the PSUs seem to be getting stuck in burst mode, but it's only a matter of time before one gets stuck again, so i should get around to doing them mod.

Thanks for the kind help, i may update this thread in the future if i discover anything or if any do fail completely.
or if the mod does not work, but i'm really hoping it does.

[RukyCon]

The load resistors did nothing, the power supply started pulsing anyway. The last ideas i have might just be me grasping at straws, but i wonder if the fault could be caused by either the control chip having some odd fault that cannot be triggered by anything other than letting it run for extended periods of time, or if the optocoupler is bad. Since this fault is intermittent, it's very hard to make it happen, but i might try desoldering one of the legs of the optocoupler to see if that may trigger it, and if it does, i may try replacing the optocoupler.

[sam_sam_sam]

My first thing would be to replace the optic sensor and see if this makes a difference one I had a switching power supply that was acting weird I figured I would try this first and that was was wrong with

If still keep acting up then try replacing the switching power supply regulator and see if this resolves the issue

By any chance did you replace the 22uf capacitor if you have I would recommend this first if you have a a capacitor rated for 50 volts I would use it instead of the 35 ones

[RukyCon]

My first thing would be to replace the optic sensor and see if this makes a difference one I had a switching power supply that was acting weird I figured I would try this first and that was was wrong with

That's what i did, but before doing so, i ran a little test to see how the PSU behaved with one side of the optocoupler disconnected, and the results of that are:

Primary side disconnected: No output.

Secondary side disconnected: Pulsing output.

So now knowing that, i went to grab one on a scrap PSU (since i had no loose ones on hand), installed it, and so far it works, but i'll have to see how well it works in the long run.

By any chance did you replace the 22uf capacitor if you have I would recommend this first if you have a a capacitor rated for 50 volts I would use it instead of the 35 ones

I was about to do that, only to realize that i goofed on the voltage, because the cap on the board was already a 50v cap.

I'll update this thread if anything happens, but i really think it will work this time.

[sam_sam_sam]

Well I am glad that you got it working again