Need help identifying circuit

Thread Starter

liamstears

Joined Jan 31, 2013
4
Hi all, I hope some clever minds can help me decipher a circuit and work out what's going on to hopefully reengineer parts to make a project work. That's a mouthful lol

So basically to sum it up, in my car I have a reverse camera that works perfectly on the stock head unit however on a replacement head unit that uses a standard RCA jack the picture quality is worse.

This is a simple case of the signal type being wrong for the input type on the new head unit but I need to work out how to convert it correctly.

I have taken apart the old head unit to try and work out what's going on but my electronic knowledge is limited. From what I can see it seems that the input signal is of a balanced type and I believe the original head unit has some sort of balun or what I believe is prob more likely is it uses some sort of differential signalling and there is a receiver that I need to replicate.

I have attached some pictures

So at the bottom is the input (direct from the camera), I've labelled up the 2 input wires and these also have a third shielding wire I haven't labelled

These go through a resistor and capacitor network into an unknown chip labelled "LMW37". This chip has the 2 input pins, a ground and a 4th pin. The 4th pin goes through a couple resistors and then I have marked it as "output". There is 3.3v supplied at this point. I have also attached a picture of the opposite side of the board and circled in red where I get continuity from where I have marked "output" and this goes into this other IC which I guess supplies the 3.3v

I hope someone can take a look and at least steer me in the right direction, I really need to know what this "LMW37" is and what it's function is as I believe it is the key to working this out and getting the useable stable signal that I need for the new head unit.

Thanks in advance

COMPONENT_VALUES.jpgPCB_TRACKS.jpgOPPOSITE-SIDE-SHRUNK.png
 

Irving

Joined Jan 30, 2016
1,174
Can't find any reference to that specific device, but my guess is that its an active balun (BALanced to UNbalanced converter).
 

Thread Starter

liamstears

Joined Jan 31, 2013
4
Can't find any reference to that specific device, but my guess is that its an active balun (BALanced to UNbalanced converter).
Thanks for the reply

I believe you are right but I am still stuck at a point where I need to try and replicate this circuit and turn this signal into a useable signal

Do you have any ideas? I would love to try and get this working and happy to get some bits to experiment, is there anything I can do to help with this?

How would I get the signal I am after from this? If I unsoldered the parts from this PCB for testing how would I go about this? I can see a 3.3v supply would be needed but how does that get separated for a normal video output? Normal RCA composite video feed is around 1v right?

Really appreciate any help or input
 

RPLaJeunesse

Joined Jul 29, 2018
158
I'm fairly sure the LMW37 part is nothing more than a transient protection device. The balanced to unbalanced conversion would be via a differential amplifier with the appropriate signal bandwidth. It will have at least 6 terminals, with two connected somehow to the vias off the 2k2 resistors. Look for backside or internal PCB traces from those vias.
 
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