12V 10A CCTV camera system power supply pulsating

[rddube]

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

before do anithing, do exactly one more time very same measurement, write data to compare.


my analisy

point A is far end of +, our reference of this test
probing ground
point D is maximum 166.6 through jumper wire
point F slightly lower 166.1
pin#1 dramaticaly lower 164.2, on sam plane with F, were is 2v lost?!?

point C near cap 165.3... something is pulling it down (mosfet try switch)
point B 164.3 (27.2mV ripple present)
point E 165.2 no ripple! there is only a 000 resistor between point E and B.


So, check what is going on between point F and pin#1, also point B and E, where is lost 1v and ripple? Check 000 resistor, it is not posible it is ok.
Is this make sense to you?


Your board may suffer of circular crack arround solder point, and when you measure this, you push it with probe and connect again with track, and all seems ok, but it is intermitten.

Ok, redid the readings with my other multimeter, and this is what I get (see photo).

[rddube]

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

Also, after taking the readings, I took out the mosfet on the primary side and here's a photo, and the readings it gives me in my component tester (there are 3 screens).

[CapLeaker]

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

Now run this PSU without the mosfet and measure the pins on the PWM

[CapLeaker]

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

Btw fix that solder joint on point A. Looks to me suspicious. Matter effect reflow all them solder joints that you
A: didn’t touch yet
B: looking shady like point A in the picture.

[rddube]

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

Ok, so took the readings on the PWM without the primary mosfet in and fixed the suspicious solder joints (I think I've now reflowed the whole board ):

Results

Pin 1 - GND
Pin 2 - .1V to 1.2V jumping around
Pin 3 - 16V to 19V jumping around
Pin 4 - .012V to .263V jumping around
Pin 5 - .2V to .86 V jumping around
Pin 6 - 0V
Pin 7 - 12.4V to 15.7V jumping around
Pin 8 - .292V to 1.18V jumping around

[CapLeaker]

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

Crazy thing. You did get kind of a different result if I compare your last results with those in post 122. But yet the darn thing does kinds the same shit what it did before. Now I am out of ideas, besides replacing every component one by one. Personally I think something went high resistance or open.

[harp]

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

Please do exact measurements of all ic legs (without mosfet) in AC setting mV.
Also, check the output DC without load and mosfet.

Till now, I was thinking that jumping oscilations came from mosfet who try to start transformer windings... when is mosfet out, the transformer is disconnected from current path? From where the exactly same oscilations now came from?
Seems to the big current is not involved anyway...

[petehall347]

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

any news yet ?

[rddube]

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

Hello everyone, sorry for the delay in replying, have been extremely busy at work and was just completely exhausted by the time I could get to work on this. It's the weekend now, so here goes, measurements of all ic legs without mosfet in AC setting mv:

Pin 1 - 0mv
Pin 2 - 0mv to 478mv jumping around in between randomly no fixed delay
Pin 3 - 0mv to 622mv jumping around in between randomly no fixed delay
Pin 4 - 0mv to 462mv jumping around in between but synchronously, like it was timed
Pin 5 - 0mv
Pin 6 - .8 to 2.2mv
Pin 7 - 0 -657mv jumping around randomly no fixed delay
Pin 8 - 154mv to 420 mv jumping around randomly no fixed delay

Output without load and mosfet is .02DCV

[harp]

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

Allmost all jumping arround...

It is kind of contradictional, but it is what it is. Mosfet is out. Mains 163v have two big capacitor and nothing to load, but it is present 0.6v ocasional ripple...
Pin#3... it is now only connection with power through 1.5M resistor.
Pin#6... sense resistor flow 10mA for nothing?

So, desolder IC from pcb (no mosfet no ic from now), and do DC and AC measurement on IC pads, I am interesting is still pulsating... do same DC reading on secondary output without load.

Pause here to discuss on forum with results...


Next I will do, is to desolder everything, but everything at all on primary side, clean pcb truely, inspect every (unpopulated) track end-to-end and double-time for 0.0 ohm resistance and visual.
Check separate each desolder component, make note... I suggest that not soldering it back that component, but use some other from scratch board.
For 000 resistor use instead a wire, and ommit placing any extra unnecesary component apart from bare bone test IC circuit, use IC socket on now on, it is possible that ic (batch) is faulty.
Then scrape on pcb a little notch in isolation coating like tear shape next to every THT pin, to reach fresh copper, put back fully tested component in a fully tested track and stretch tin solder to flow this area.
After soldering each component, test fot continuity and shorts with near area.

Suggestion from others?

[petehall347]

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

i would be changing the 1.5 meg resistor first .

[lotas]

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

i would be changing the 1.5 meg resistor first .

Yes, it can be reduced a little and set to 1.2 MOm.

[Alimash]

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

Just a thought, a similar issue happened to me, and i solved it by simply resoldering the whole board, it turns out some joints has moisture.
It took me a lot of time to figure it out.

[rddube]

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

Hey Harp, I appreciate your help and the effort in trying to diagnose this, but I am at a point where it's almost a no go with this thing! I think I'm going to try what Alimash suggested and if that doesn't revive it, well it will have been a long adventure..I'll keep you posted on my resoldering of the whole board.

[CapLeaker]

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

I wouldn’t trust this psu anyway much and replace it with a Meanwell that fits.
This being said, I would use this old power supply as an “educational” piece. Maybe even put it on the side in later to fix pile when the weather gets bad or you are bored or something. Then go at it again. I did this a few times and the end was successful.

[petehall347]

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

would be nice to find out what is the fault after 6 pages ,,
just noticed the last voltages are ac so that threw me a little .
whatever it is will be something really silly as those things get overlooked often . most of my call outs turn out that way after the so called experts have had a go at whatever it was ,

[rddube]

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

Ok, so I gave this thing a last shot and redid all the soldering on the entire board thinking it might be the solution, but alas, no still the same erratice voltages. On the startup cap, I get between 11.6V to 15.2V jumping around in between.

[CapLeaker]

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

I am still saying it acts like there is something high in resistance or open somewhere on this darn thing.

[rddube]

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

I am still saying it acts like there is something high in resistance or open somewhere on this darn thing.

I checked almost every component, changed the output capacitors, etc. Redid all soldering and even changed the PWM chip again just to make sure. Same symptoms.

Starting to think there is something wrong with the transformer but did check that too and it's a complete mystery!

[harp]

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.

R_J, can you please explain how exactly external psu will blow it up, current pathway?
Supose to both wall psu adapter have not direct ground pin.