12V 10A CCTV camera system power supply pulsating

[harp]

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

It is not neccesery to remove secondary diode again, unless (like I mentioned before) you feed 12Vdc to output and simultaniously power psu from mains 220Vac, due to specific testing purpose.
So yes, just feed 12v and check again pin1&3 of TL431 and primary side of optocoupler, maybe to try reverse probe, or other dmm... if in off state is 3k reading accross pin3&4 of opto, then when interLED power on must be some lower reading, dont you think?

[CapLeaker]

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

Ok, cleaned the probes and deoxed them, but the lowest I get with very high quality probes is .5 ohms, there is no way to 0 it. Whereas the cheaper tester Tais TA118A is dead 0 ohms when connecting the 2 probes together. It cost +- 40$ compared to the Fluke 87 V which had cost me over 500$. Probably need calibration and cleaning, but they're asking over 300$ CAD to do this at Fluke, not worth it.

If you get real good probes, you will get it down to 0.2ohm. Flukes usually do not go down to flat zero as it measures the resistance of the leads. She is fine and well within tolerance.

[petehall347]

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

was the ic changed for a new one yet ?

[rddube]

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

It is not neccesery to remove secondary diode again, unless (like I mentioned before) you feed 12Vdc to output and simultaniously power psu from mains 220Vac, due to specific testing purpose.
So yes, just feed 12v and check again pin1&3 of TL431 and primary side of optocoupler, maybe to try reverse probe, or other dmm... if in off state is 3k reading accross pin3&4 of opto, then when interLED power on must be some lower reading, dont you think?

Ok, redid the test and here is what i get when I inject 12v at the output:

TL431 Reference 2.6V
TL431 Cathode 1.8V

opto pin 3 & 4 no power : .680M ohms
with 12 V on output: 105 ohms

[rddube]

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

was the ic changed for a new one yet ?

Yes the IC was changed for a new one.

[harp]

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

Ok, redid the test and here is what i get when I inject 12v at the output:

TL431 Reference 2.6V
TL431 Cathode 1.8V

opto pin 3 & 4 no power : .680M ohms
with 12 V on output: 105 ohms

Now opto look ok, so it is prove that led and transistor worked.
For TL431, I guess it is also ok, but not sure.

My suggestion is, that all the time that going with testing and troubleshooting, you have permanently soldered dummy load on output, say 100R few wats. When you find the problem, voltage will arive on output, otherwise, without load may pulsate anyway.
Notice down first initial measurement of this setup, voltage on (loaded) output, for future reference.

Somebody earlyer suggested to connect larger capacitor on pin7. To dont overbutched your pcb, try to add temporarly parallel biger and bigger caps on other side direct on solder points, or use fine aligator clamp. Monitor output, if any change and compare?

I highly suggested that you use a bulb current limiter always when troubleshooting with live mains.


Also, on your post #102 when took off transformer, have you write readings of resistance and inductivity?

[CapLeaker]

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

Ok, redid the test and here is what i get when I inject 12v at the output:

TL431 Reference 2.6V
TL431 Cathode 1.8V

opto pin 3 & 4 no power : .680M ohms
with 12 V on output: 105 ohms

That's what I was looking for earlier. There isn't much more to proof that the secondary is o.k.
You got the primary and the transformer still as suspect.

[petehall347]

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

am sure this will have been looked at already in the pic .
on another thought i dont really understand this circuit but i might have expected the gate of the chopper transistor to be getting something other than 0v . Pin 8 - 9.54kΩ to ground .is this ok ?

[petehall347]

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

another thing is have the bad solder joints been rectified yet ? i see a few on the first pic .

[stj]

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

am sure this will have been looked at already in the pic .
on another thought i dont really understand this circuit but i might have expected the gate of the chopper transistor to be getting something other than 0v . Pin 8 - 9.54kΩ to ground .is this ok ?

that image is the winding to power the chip once running.
thats why i asked about that diode on pin7

[rddube]

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

My suggestion is, that all the time that going with testing and troubleshooting, you have permanently soldered dummy load on output, say 100R few wats. When you find the problem, voltage will arive on output, otherwise, without load may pulsate anyway.
Notice down first initial measurement of this setup, voltage on (loaded) output, for future reference.

Somebody earlyer suggested to connect larger capacitor on pin7. To dont overbutched your pcb, try to add temporarly parallel biger and bigger caps on other side direct on solder points, or use fine aligator clamp. Monitor output, if any change and compare?




Also, on your post #102 when took off transformer, have you write readings of resistance and inductivity?

Ok, so tried with a load, no output at all. Without load, pulsating from 4V to 6V.

Tried a 47uf capacitor, still same result - with load no output, witout load pulsating between 2 - 3V.

When I took off transformer I did not write resistance but I checked and it all seemed good. Don't know how to check inductance however.

[rddube]

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

another thing is have the bad solder joints been rectified yet ? i see a few on the first pic .

Yes, I redid almost all the solder joints.

[rddube]

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

I'm about to give up on this thing unless any of you have any other ideas, I think we spent enough time trying to resolve this. Many thanks to all of you!

[rddube]

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

I was thinking in putting in a 1uf cap instead of the 10uf cap. What do you think? Usually, startup caps are 1uf 50V, so maybe this could be the problem because when I put a 47uf cap it just didn't make any difference.

[stj]

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

22 or 47uf would be better
but check the related diode too

[harp]

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

I'm about to give up on this thing unless any of you have any other ideas, I think we spent enough time trying to resolve this. Many thanks to all of you!

I think that your chip have no needed voltage to operate in pin7. So how about that you disconnect primary aux diode and connect 2x9v battery (18Vdc) on that resistor for pin7. Wait aproval if this idea will provide power to ic to test.

If is all component around the board is ok, that only left a transformer. Inductance can measure with "transistor testers", when is out. When you choose to step ahead to rewireing it, know that this not impossible, and also reffer to repair electronic...

https://m.youtube.com/watch?v=ODcqLmg7vR4

[CapLeaker]

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

At the end of the day it isn’t that wild, because it is just a singe voltage PSU. You can always replace it with a different one. To me there is somewhere something open or high resistance, or the transformer got a shorted winding. To measure the transformer you need a ring tester, you can’t measure its resistance besides an open.

[rddube]

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

At the end of the day it isn't that wild, because it is just a singe voltage PSU. You can always replace it with a different one. To me there is somewhere something open or high resistance, or the transformer got a shorted winding. To measure the transformer you need a ring tester, you can't measure its resistance besides an open.

I do have a ring tester but not too sure how to use it. Also, I've been told that they are not that accurate, but it's the one that you build with a kit. I could with some guidance test the transformer - it's got 2 X 3 connected legs on the secondary side and 4 legs on the primary side.

[CapLeaker]

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

That’s o.k. Can’t be worse than a Effed up measurement. You just have to know what windings are where and on which side and you have to measure one winding to the other winding etc. One more test you also could do is an insulation test on the transformer. Maybe it’s looking good like that, but starts arcing when under higher voltage? I don’t have a ring tester, but I do have a 1000v Isolation tester.

[rddube]

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

That's o.k. Can't be worse than a Effed up measurement. You just have to know what windings are where and on which side and you have to measure one winding to the other winding etc. One more test you also could do is an insulation test on the transformer. Maybe it's looking good like that, but starts arcing when under higher voltage? I don't have a ring tester, but I do have a 1000v Isolation tester.

Ok, so I took the transformer out. The winding which is the feedback winding on the primary side looks fine with the blue ring tester. The other winding on the primary side comes out as a short, but then all windings on the secondary side all show up as shorts (there are 3 legs connected together and 3 other legs connected together, if I measure between both 3 legs, it shows up as short.).

Do I have to disconnect the 3 legs connected together before taking measurements?