M70 line in tapped on PCB, but question.....

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blu_fuz

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So I have the line in pads tapped on the pcb in my M70. The bluetooth module is working.


Apparently the RCA jacks are a 'switched' type where you have to have a physical rca plug pushed into the jack for the input to work.

Sort of like how headphone jacks work where the normal speaker signal is sent through them until a headphone is plugged in, then the sound is routed to your headphones and turns off to the speakers.

How can I bypass having to plug something into the jack?

This seems stupid easy but I'm going mental over this....
 

blu_fuz

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When a rca plug is not in the jack, the common (-) and positive (+) pads touch in the back of the jack.


Why?

The way I see it, there is no other way to tap the jacks on the M70.
 

Superduper

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OK here is something for you to try:

jvc_rc-m70_line-in_tap_location.jpg

The design of shorting the (+) to ground when no rca jack is inserted is a good design because it prevents noise from entering the audio signal path when that circuit is not being used. Low level signals are very prone to interference. The cap and resistor isolates the circuitry on both sides. Try tapping into the circuit at the other side of R721/R821. Check it and report back. A small amount of the signal will get shunted to ground but enough should pass to work.
 

blu_fuz

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Superduper said:
OK here is something for you to try:

jvc_rc-m70_line-in_tap_location.jpg

The design of shorting the (+) to ground when no rca jack is inserted is a good design because it prevents noise from entering the audio signal path when that circuit is not being used. Low level signals are very prone to interference. The cap and resistor isolates the circuitry on both sides. Try tapping into the circuit at the other side of R721/R821. Check it and report back. A small amount of the signal will get shunted to ground but enough should pass to work.
I might try that later. For now I just bend the (-) tab away from the (+) tab at the back of the RCA jacks. I put the info in my M70 BT mod thread. I saw that there was a cap and resistor in the circuit just after the RCA jacks so I didn't want to feed signal into the system after those. Its all good right now:


IMG_3938.JPG
IMG_3939.JPG
 
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