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ADV7180, no color, out of lock, temperature dependent

Question asked by Konta on Mar 10, 2015
Latest reply on Mar 11, 2015 by Konta

Hi,

 

I am using two ADV7180 (40-pin) in my design. The first is only connecting to an analog input on Ain[1], the second receiver is connecting to Ain[1] and Ain[2]. The system shall use two separate video input pictures, selecting one picture from decoder one, and the second picture from one of the two channels on the second decoder. I have a CM-filter on all the analog video inputs, and the standard AC filter as stated in the datasheet. The two decoders are implemented in the same way, only differing in using one or two analog inputs.

The analog video input is a CVBS signal, PAL or NTSC type.

 

My problem is that only the first decoder is working sufficiently, the second decoder is showing a bad picture without color. The second decoder is stating a out of lock. Inspecting the analog signal into the decoders (on pin.23), indicate a rather good signal. Just a bit noise can be seen on the channel to the second decoder, the decoder that shows the bad picture.

I have tried to use an external clock source (replacing the oscillator on the PCB), I have tried to bypass the input filters, I have tried to pull the AC decoder side signal to GND by a 1Meg resistor, I have tried to re-scale the analog video signal input (through my CM-filter), etc. For now, I suspect that this is a PCB Layout problem.

 

However, when using a cool spray, I observe that the picture is close to perfect if I cool down the IC of the second decoder. Nothing happens if I cool down the feedback-loop filter to ELPF pin, or if I cool down the filter cap. between the VREF pins, of if I cool down the decoupling capacitors, of if I cool down the oscillator... Cooling down the filters does not change the picture. The only change is seen if I cool down the top packet/plastic-hosing of the IC.

 

 

Is there anything I should try within the chip, using specific registers, that might help me indication a bad PCB Layout?

To make a new PCB Layout is expensive and time consuming, nor have I any guarantee that the PCB is the reason for failure. It would by this be great to be able to increase the suspicion of a bad PCB layout.

Or maybe I am wrong, indicating that this is a PCB Layout issue?

 

 

Sincerely yours

Konta

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