12V 10A CCTV camera system power supply pulsating

[rddube]

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

Thanks R_J for such good learning details. Will try with a 470ohm resistor and wil also make sure all charges are depleted before taking measures. Will report back shortly.

[rddube]

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

So I decided to take out that variable resistor and test out of circuit, and it measures a perfect 510ohms in the middle position.

So I took measurements of that area under the board and this is what I have (please see picture).

What do you think?

[R_J]

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

The resistance looks ok, Reference and Cathode are reversed on your picture. Is this a TL341?
You might want to check R13, R14 and 000Ω at loc. ZD2

[rddube]

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

The resistance looks ok, Reference and Cathode are reversed on your picture. Is this a TL341?
You might want to check R13, R14 and 000Ω at loc. ZD2

Hi R_J,

It is a AZ431 which I think is the same. I also think I identified the reference and the cathode correctly, because if you turn the board around, that's how it is positionned. I'll check R13, R14 and the 0ohms at loc ZD2 and report back.

[harp]

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

I also think I identified the reference and the cathode correctly, because if you turn the board around, that's how it is positionned.

You are incorectly labeled TL431 pins on picture. Reference pin #1 is that one who have voltage divider attached to it, thus 11k8, 2k4 and pot. In datasheet it is presented from top view, you cant just rotate it 180 deg...


And maybe another point, I not sure:

What is weird, is when I remove C4 and test, I get no more pulsing on the top pin of R10 (a nice clean stable 18V), but then I get no output on the secondary side, nothing?

Can you remove C4 again and measure voltage on all pins of pwm, to compare if also other pulsating stops .

[R_J]

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

Hi R_J,

It is a AZ431 which I think is the same. I also think I identified the reference and the cathode correctly, because if you turn the board around, that's how it is positionned. I'll check R13, R14 and the 0ohms at loc ZD2 and report back.

That datasheet shows the TOP VIEW of the ic, not the bottom view, The reference pin does not drive the optocoupler.

[rddube]

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

That datasheet shows the TOP VIEW of the ic, not the bottom view, The reference pin does not drive the optocoupler.

Sorry R_J, you are correct, my bad. Gets confusing. I'll get on with the tests that you suggested and also those suggested by harp. Thank you for sticking with me! Attached is corrected photo.

[rddube]

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

You might want to check R13, R14 and 000Ω at loc. ZD2

R13 measures .998K ohms
R14 measures 2.209K ohms
000 at loc. zd2 measures 0 ohms.

[rddube]

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

And maybe another point, I not sure:


Can you remove C4 again and measure voltage on all pins of pwm, to compare if also other pulsating stops .

C4 removed, no more pulsating, 6.1V (steady) on output of secondary.

PWM:

Pin 1: GND
Pin 2: .11V steady
Pin 3: 18V steady
Pin 4: .1335V steady
Pin 5: .323V steady
Pin 6: .044V gradually decreasing to .038V
Pin 7: 13.77V steady
Pin 8: .013V

btw, C4 is a 10uf 50V cap changed from the original for a very low ESR cap. It was not present on the board during the above test.

[harp]

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

With C4

Pin 1: GND
Pin 2: .1V to .3V oscillating
Pin 3: 16V to 19V oscillating
Pin 4: 0V to 1.3V jumping around sometimes to 3.2V
Pin 5: same as pin 4
Pin 6: 0V, sometimes shows .1V or .2V then 0V
Pin 7: Oscillating between 11V and 15V
Pin 8: .001V

Without C4

Pin 1: GND
Pin 2: .11V steady
Pin 3: 18V steady
Pin 4: .1335V steady
Pin 5: .323V steady
Pin 6: .044V gradually decreasing to .038V
Pin 7: 13.77V steady
Pin 8: .013V

Pin 7 vdd needs to be at 16.5v or above for the ic to operate

How to isolate the problem - I dont know if it is right way, but grand masters are watching and can correct me Do not anything without their aproval.

I will desolder D2 and feed 18V into pin#7. With this can be isolated eventualy problem on aux windings. You may observe current draw also.

Second, if first idea do not work upgrade to second idea - desolder secondary output diode and feed output of psu with 12V, to check feedback. When you adjust trimpot, some changes must see on primary side, eg change gate voltage in AC mode.
Double check R4 and R6 on gate.

[R_J]

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

You can NOT feed an external voltage to pin 7, If you connect an external power supply ground to this power supply HOT ground you will blow it up.
Disconnect D2 and see if you have the same pulsing problem, and the voltage on pin 7 stays the same, if it does I suspect either R7 or the feedback winding on the transformer could be open.
The gate drive PWM is operating at 65KHz how do you expect to see a change in duty cycle with your meter?
I would try unsoldering the primary side of the optocoupler and see if the voltage on pin 2 is at 6v, and be careful not to short the ic pins when checking.

[rddube]

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

You can NOT feed an external voltage to pin 7, If you connect an external power supply ground to this power supply HOT ground you will blow it up.
Disconnect D2 and see if you have the same pulsing problem, and the voltage on pin 7 stays the same, if it does I suspect either R7 or the feedback winding on the transformer could be open.
The gate drive PWM is operating at 65KHz how do you expect to see a change in duty cycle with your meter?
I would try unsoldering the primary side of the optocoupler and see if the voltage on pin 2 is at 6v, and be careful not to short the ic pins when checking.

Ok, R_J, got ya. When you say "Disconnect D2 and see if you have the same pulsing problem, and the voltage on pin 7 stays the same,", do you mean after reinstalling C4 or I leave C4 out? Also, is the feeback winding the one I measured in post #19 ?

[R_J]

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

C4 needs to be in place or the ic will never ever try to start. If you disconnect D2 and the pulsing stayed the same then that could be where the problem is. I suspect the pulsing will stop as a result of no run voltage from the feedback winding.
I re-read that post #19, seems a long time ago, so the winding is not open.

I would try disconnecting the optocoupler on the primary side to see if you get closer to 12v on the secondary output. It may not work due to all the safety features of this ic.

[rddube]

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

D2 removed, pulsing on the secondary output and on pin 7 of the PWM, pulsing from 11V to 15V approx. For the next test (disconnecting the optocoupler on the primary) do I reinstall D2?

[R_J]

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

So nothing changes in the operation of the power supply if D2 in in circuit or not? if that is the case the feedback circuit can't be working.
With D2 anode connected and the cathode in free air, check if there is any voltage on D2 cathode, or if you can, place a 10µf cap between hot ground and D2 cathode and see if that circuit charges the cap. basically have u1 pin 7 disconnected from the circuit.
If you have another diode try replacing D2 it might be failing

[rddube]

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

Ok, so just to make sure I get this right, I place a 10uf cap between D2 cathode and hot ground (what is hot ground, is it primary ground or same ground as pin 1 - dumb question) ?

Also R_J, I did have another D2 diode that I scavenged from old boards and exactly same behavior. I tested both with my fluke multimeter in diode mode and both test good.

Another question R_J, should I remove the transformer to check the feedback coil? What if it gave me the wrong reading because it was connected in circuit?

[R_J]

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

There is no need to remove the transformer, the feedback winding can be checked when D2 is out of circuit, The reason I suggested to add a cap to D2 so it can charge and give a proper voltage, basically it is acting as C4, so use C4's ground. Hot ground is the primary ground, basically the main filters negative lead or U1 pin1.

By isolating u1 pin7 we can check the transformer winding, the 22Ω resistor and D2 to make sure it is supplying voltage.

[rddube]

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

Should I remove C4 ?

[R_J]

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

No, you need C4 in place so the ic will actually start, (pulse) without C4 the ic will not start and you will not get any secondary or feedback voltages.

[rddube]

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

ok, so here goes!