12V 10A CCTV camera system power supply pulsating

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

Hmm my 179 only goes to 100khz and my 289 to 400khz. Try measuring at the PWM

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Specifications: Fluke 87V Industrial Multimeter
Frequency Maximum frequency 200 kHz
Accuracy ±(0.005% + 1)
Maximum resolution 0.01 Hz

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

First see how high of frequency your DMM can measure.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

with the frequency function on your meter if it has it .

Yes it has the frequency function, but how do I set this up? I need to resolder the transformer and put the frequency meter on the chip pins? What is the FET ?

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, the primary being the one on the right in the photo (I think) measures 465 uH and the secondary measures 17.03 uH. When I measure another transforer I have with same configuration, I get 474 uH on the primary and 17.03uH on the secondary. Not sure what that means however?

Ok. So this is what I would expect. The primary winding is good then. The auxiliary winding would show a short as the wire length is much shorter than the primary one. The secondary probably shows a short too, since the wire length is also short and a thicker wire is used. Plus you actually measured 3 windings at the same time.

More uH means more inductance, which also means more wire turns.

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, thanks Petehall347, but how do I measure that?

with the frequency function on your meter if it has it .

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

basically the fet should be switching on and off somewhere over 10khz . this being controlled by the ic .

Ok, thanks Petehall347, but how do I measure that?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, the primary being the one on the right in the photo (I think) measures 465 uH and the secondary measures 17.03 uH. When I measure another transforer I have with same configuration, I get 474 uH on the primary and 17.03uH on the secondary. Not sure what that means however?

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

Not sure how to do that?

basically the fet should be switching on and off somewhere over 10khz . this being controlled by the ic .

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

The secondary windings should measure close to a short less wire and thicker. The primary winding should show somewhat of a resistance since it has the longest wire. Look up at how a switching transformer is constructed. There are quite a few variables like wire length, thickness and coating thickness. When a primary measuring the same at 0.1 ohm like a secondary, I smell fish.
I do have another idea. Measure the inductance of the primary and secondary if you can.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

did you check the switching frequency when testing it when it was all together ?

Not sure how to do that?

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

did you check the switching frequency when testing it when it was all together ?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

This short-circuited turns meter measures only the primary (power) winding, it will not show on all other (secondary) windings.

Lotas you're right, Momaka gave me an idea and I pulled 2 other transformers from scap boards with pretty much the same winding configuration on the primary side, and both show the exact same results. So in the end, I think my transformer is good, the problem is elsewhere, but where??

[stj]

Re: 12V 10A CCTV camera system power supply pulsating

if your using a ringer, shorted secondary's usually supress the field in the primary and show up anyway.

[lotas]

Re: 12V 10A CCTV camera system power supply pulsating

Well, not very good news as one of the primary windings shows a tremendous short!

When measuring with ohmmeter, the shorted winding gives me .1 ohm, but then the good windings also give me .1 ohms.

So I guess we're toast?

This short-circuited turns meter measures only the primary (power) winding, it will not show on all other (secondary) windings.

[momaka]

Re: 12V 10A CCTV camera system power supply pulsating

So I guess we're toast?

Maybe (likely?).
The best way to find out is to open/break the transformer and see for yourself.

But before doing that, there is STILL a way to test if the rest of this PSU is working: get another 12V power adapter and take the transformer from that. The donor adapter doesn't need to be rated for 12V and 10A - any switch-mode adapter will do, even one rated for just 1 Amp. The only thing to look for is an adapter that has a transformer with main and aux. windings on the primary and single output winding on the secondary. And the adapter has to be the same topology - discontinuous (flyback), which is what basically over 99.9% of small adapters use. So it should be pretty easy to find one. Once you do, just match the pins of the windings of the new transformer and that's it. (Hint: you don't need to solder the donor transformer to the PSU board - just use wires to connect the pins to the right spots. Old transformer needs to be removed for this to work, of course.)
Now, there is a small chance the aux. winding from the donor transformer may be too low in voltage and not able to power the primary-side IC... but hey, still worth a quick test if you have some junk adapters around.

DO use an incandescent "dim bulb tester" when testing the PSU with the "new" transformer, just in case. Dim bulb tester:
https://www.badcaps.net/forum/showpo...4&postcount=70

If the PSU does happen to work with the donor transformer, then you know yours is bust for sure... in which case, rewind it for a challenge?

Yes, failed transformers are rare, but they can happen. A blowout on the primary can cause that sometimes, and it usually is the main winding on the primary that bites the dust. The secondary is wound with thick wire and can dissipate a lot of heat, even when fully stressed.

You've come this far, so why not take it a notch further.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Well, not very good news as one of the primary windings shows a tremendous short!

When measuring with ohmmeter, the shorted winding gives me .1 ohm, but then the good windings also give me .1 ohms.

So I guess we're toast?

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

I agree with RJ. That’s how I see the transformer construction too. Showing a short with the ring tester on the primary winding, it’s game over.
It does make sense, since everything else on the board has been triple and quadruple checked in wich ever what way, plus the primary had blown components.

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

The secondary side likely has 3 separate windings to supply the higher current (10a)
The primary side has the feedback winding (blue) and the main primary winding which likely has a thermal fuse, the middle pin is where one end of the thermal fuse is connected.
The primary fuse is likely between A & B or B & C The primary winding will be between the other pins

[harp]

Re: 12V 10A CCTV camera system power supply pulsating

First make a schematic of transformer windings on paper, using multimetar determine each coil and confirm no continuity to others coil, neither primary or secodary coils. On that schematic add note of all measurement you done.

On pcb the secondary is all connected, but it seems there is a separate 2 coils. If one of coils is defect, and parallel connected to good one, nothing gona work.
And get rid of all this solder balls around pins!

I thing that on secondary is two coils, but check.
On primary main coil is probably center tap, and it should be on half resistance from each side. I see suspicious markings on center tap pin, just like sparking...?