EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: kolbep on July 08, 2013, 01:50:27 pm
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Good Day.
I have a customers site, where we are running their CCTV system's Composite Output into a Video Distribution amplifier, and from there it feeds 2 monitors in each flat using the Composite video in (the same type that they put in cars for headrest monitors, etc. But they are supplied by Securiprod).
This system was working well, until the monitors started failing (Inverters packing up, boards corroding), the site is right on the beach.
I quoted them on replacing the faulty monitors with Provision-ISR monitors, similar, but these come with a 3 yr warranty, and claim to be made to be on 24/7.
So I put the new monitors in. And it looks like their AGC goes crazy
[ The picture is very bright, I had to turn the brightness on the monitor down to it’s minimum, and it is still very bright.
Also the picture Flashes very bright, and then dims down. And then repeats the cycle continuously.
(only on the new ones, the old type still working fine).
You can see sortof what it is doing in this youtube video i took with my cellphone :
Video0000 (https://www.youtube.com/watch?v=nGKyJCncndg#)
I contacted the South African dealer for the Provision-ISR monitor, and they came back with this BS :
We have checked the screen based on your information and it looks like that the issue is the amplifier that is not fully synchronized with our screen it could be due to resolution compatibility between the amp and the screen.
Unfortunately there is nothing we can do from our side except to advise you to change the type of amp you are using only for the simple reason that our screens carry a 3 year guaranty and are design to work 24/7 so its more likely that your other type screen will give up with time.
So I ask them to find a distribution amp that will work, and they can not find anything.
I need to get this job finalised, so I have traced the schematic of the distribution amplifier (Transistor based 1 in to 8 out.) It has a 7809 Regulator, but as the other monitors are fine, I have not bothered tracing the PSU section.
Please can somebody see if there is anything that will cause some monitors to mess around, but the others are fine (no matter what the gains are set at).
I am not too much into Video design, but should'nt the In and Outs have 75R resistors on them?
Thanks
Peter
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Turn down R5.
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Tried that. did not have any effect, except for the picture noise altering (that is why I think the AGC is not liking something).
I know it is not the monitor, cos If i hook it straight up to the input before the amp, then it is ok. The amp is definately changing something else...
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It is a very odd amplifier. No input bias so it relies on the video for it, and then cuts off the sync pulses quite hard. Tried another amplifier? You might have to come up to Durbs and buy one from any of the usual dealers.
Space Tv has a CD108-2 8 output distribution amp ( I buy from them but have never used this one yet so YMMV ) and a 4 output that is a lot cheaper.
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Bingo. Changing the amplifier worked :clap:
I kept the transistor based amplifier for the old type of LCD screens,
and i put in a distri. amplifier that is based on a Comlinear® CLC4601 Quad 550MHz Amplifier chip.
So the DVR composite out now goes to the new amp first, port 1 of the new amp goes to the in of the old amp, and the other ports of the new amp run the new monitors.
Works great.
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Good to hear that Peter. Simple solution to a bodged manufacturers attempt to generate a lock in for the product.