PSU For CCTV - noise or interference in the image seen from the camera

[SoporteHR]

Hi all.

Receive a warm greeting.

I have a centralized power source for CCTV. Model SP200B S88

New, zero use.

It turns out that the CCTV HD cameras were connected, most of the cameras present noise in the image seen on the monitor.

Check, grounding, interference with other electrical cables in relation to the video cable, etc.

The source was replaced by another and the cameras worked perfectly.

Now checking at the plate level this source, everything looks good, suspecting that it was a problem of line filtering, replace the 3 capacitors of the output. (2200uf x 25v). It did not solve the problem.

Then I went to the primary session, replace the capacitor (CT) of the KA7500B that sets the working frequency. It did not solve the problem.

I also changed the capacitors of the primary 470uf x 250v x 560uf x 200v which was the ones I had at hand (Then I install the originals).

Change the capacitors that are associated with the primary transistors / mosfet. 4.7uf x 50v.

In red of one of the images, mark the components that I changed.

I consult here because I do not want to disassemble half of the source and affect the PCB tracks, just because I am doing trial and error.

They have any suggestions that may cause the interference problem.

Note: The power source does not vary the voltage before a load of more than 6 amps. The voltage is very stable, zero noise, hum or others.

Thanks.

[stj]

Re: PSU For CCTV - noise or interference in the image seen from the camera

maybe the desugn does not like long cables on the output that can act as inductors/antenna's and destabilise the feedback.

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Thanks, STJ. Nice to greet you.

Initially I also thought that.

But the probe in my test bench connected to a CCTV and the cable measures less than 1 Meter the noise is the same.

I also connected it to another camera that brings its original cable (Video-Audio + Power) and connected it directly to the source with a Plug connector. Same noise.

Y recalco que cambiando esta PSU por otra en la instalación de las cámaras del cliente, el ruido desaparece, es esta fuente que tiene el problema.

Thanks.

[CapLeaker]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Can we see the whole psu? Did you replace this psu with the exact same psu, or a different one?

[budm]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Do both power supplies, one that works and one that does not work, have ground prong?

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

I'm going to find out which PSU model they used as a replacement, since I didn't do that, if not the installer and owner of the PSU

I attach photos of the complete source.

thanks.

[CapLeaker]

Re: PSU For CCTV - noise or interference in the image seen from the camera

so how did you wire this PSU up to the cameras and the mains? I am thinking ground loop.

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

The cameras are isolated from any metal surface, plastic boxes were installed.

The cameras work well, when 12v independent adapters are used

[stj]

Re: PSU For CCTV - noise or interference in the image seen from the camera

did you scope the supply at the camera end?

[redwire]

Re: PSU For CCTV - noise or interference in the image seen from the camera

It looks like a bad design power supply, noisy and high EMI. chinese special low cost.
There is no opto-coupler? So I'm not sure how it isolates and regulates.

I would put in a larger Y-cap C7 at least 2200pF, and ceramic cap across the output electrolytics, like 0.1uF. It is missing HF filtering there.
X-cap C8 is for additional mains filtering to prevent noise from coming out there. C8 should be around 0.1uF 275VAC X2 if you want to try it.
Try put an AM radio close to it and see how noisy it is. Sometimes the feedback loop is unstable and the output voltage extra noisy, especially with a light load.

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Stj. Yes. i tried but my oscilloscope (pencil type) is very basic and does not allow you to see anything in detail. Attach one of the images. (Output without noise.jpg)

I will test the radio, before starting to review the source, the first thing I did was to place a ceramic capacitor in each chamber, without results, then I tried to add a 2200uf capacitor directly at the exit to the cameras, since I also suspected that it was a filtering problem

And finally I replaced all the output filters.

Sorry redwire, the capacitor numbers on my board refer to the 103 x 1KV capacitor. That makes ground connection.
C8 is not installed on a board, there is a resistor in place, do I place the capacitor on that resistor?

Please confirm me, to proceed with these capacitor tests

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Hi. following the recommendations of Redwire.

I removed the resistor that was in the C8 position, and installed the respective capacitor.

No changes, same noise.

By the way, yesterday the CCTV installer told me, that the source used for the cameras that replaced this one I am reviewing, is the same model and is presenting the same noise problem in the images captured by the cameras.

Thanks

[stj]

Re: PSU For CCTV - noise or interference in the image seen from the camera

it would be good to see the frequency of the noise.
it may even be some external cause like a radio transmitter - so much wireless shit about these days.

btw, are these camera's using the coax for power and video like philips used to do, or is it seperate cables?

[redwire]

Re: PSU For CCTV - noise or interference in the image seen from the camera

I'm pretty sure the noise problem is common-mode appearing at the 12V output.
Are the cameras or their video cable (shield) or the video monitors connected to earth ground? The whole system is grounded somewhere?
I would add bigger Y-cap from 1,000pF to 4,700pF to the PSU, from +12V to PE, and -12V to PE.
You could try add ferrite clamp-on at the output lead pair too. Or a few turns in toroid common-mode inductor.
C8 would only help with noise on mains, which must no be where the noise gets out.

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Hello STJ.
The oscilloscope is difficult, I have nothing to see the output frequency, but I think that there must be the problem

The cameras indicated that they were wired with UTP cable.

Hello. Redwire.

I'm going to try the ferrite in the wiring and place larger capacitors.

I will let you know the results, thanks for your time.

[!!crappy!!]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Hi, As this is a switch mode psu, you may be getting noise from the swithing itself. Have you tried placing some clip on ferrite cores with the cables to the camers wound several turns trough them. Also have you tried a linear psu to see if that cures the problem. Earthing may also be an issue

[!!crappy!!]

Re: PSU For CCTV - noise or interference in the image seen from the camera

I forgot to mention that many manufacturers leave out critical filtering components on their pcb's to save money. One find a lot of this from China based equipment.

[SoporteHR]

Re: PSU For CCTV - noise or interference in the image seen from the camera

Hello sorry, I was late today, I saw the message.

If we tried placing ferrite cores without positive results, we added capacitors in each chamber and it did not improve either.

The cameras work perfectly with the linear source, as well as with the 12vdc adapters that are also switching.

We tried another power source similar to this one that we are analyzing and they work well, the problem is this specific source.

Thank you for your time in answering me.