Advice on circuitry inside the head unit - trying to add an aux. input (large pics) - JeepForum.com
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Unread 07-02-2013, 07:11 PM   #1
RoldGold
Registered User
1996 ZJ 
 
Join Date: Jun 2013
Location: Philadelphia, PA
Posts: 284
Advice on circuitry inside the head unit - trying to add an aux. input (large pics)

So I am trying the impossible and trying to add an aux. input to the head unit. I have the infinity sound system with the 3 band equalizer.

Well I made some interesting progress today. I disassembled the head unit and found this, which I thought was interesting:



From what I could surmise, that is the connector which houses the low level signal which is yet to be preamped to the level necessary for the amplifier. Or in other words, it is the input into the preamp within the head unit. Unsure of its use I decided to further disassemble the head unit and remove that circuit board, as it turns out there are multiple circuit boards all connected to each other either with flat ribbon cables or long pins connected to another circuit board.

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This picture above shows the circuit board after being removed from the head unit. The yellowish-white connector on the far left is the connector pictured in picture number one, of which I am unsure of its use. The frontmost yellowish-white connector in the center of the picture, the one with pins, houses a wire which connects to the external connector for the speakers. In other words, it is the last place that any signal travels in the head unit before leaving the head unit and being sent to the amplifier. The rearmost yellowish-white connector in the center of the picture accepts the pins from another circuit board once installed.

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As it turns out this circuit board is called the "PCB-AMP", which makes me optimistic.

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Here are some more pictures of the circuit board. The first picture shows some IC's that I believe do the "preamping" within the head unit, but I would like some clarification, or a second opinion on what they are. The second picture shows the bottom and the large black rectangles on the top of the circuit board are the IC's shown in the picture above it.

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So it is my belief that the PCB in the pictures above is responsible for taking the low level signal generated by the AM/FM radio, tape deck, or CD player, and pre-amplifying it to the level necessary for the amplifier. I don't know for sure what it does, and I'd love some second opinions. As of right now, I am scrapping the idea of buying a separate pre-amp or transformer and increasing the power of the output of my iPod so the amplifier can "hear" it. AndyCivil, you had a good idea using the line level output provided through the iPod connector, but I reread that article and it said that the line level output of the iPod is still only about 2 volts, compared to the line level output of a CD player which was about 6 volts. So accessing the line level output through the iPod connector would not be beneficial.

Clearly this is possible to do. I posted an eBay auction that contains a modified radio that claims to have an iPod connector tied directly into the head unit. So I just need to find the right place to tie it in. I'm thinking of experimenting with that connector pictured in the first picture.

*FIXED* I am still trying to get the radio to think that it is installed in the car, even though I have it powered on my workbench with a power supply. For whatever reason it thinks only the battery is connected, and therefore won't power on but only will give me the time. *FIXED*

So any comments at all are greatly appreciated!

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1996 Grand Cherokee Limited 4.0L
PSC Steering Gear; NP249 w/ new VC; Moog TRE's, Track Bar, Stabilizer bar bushings and endlinks, control arm bushings
Still no lift, and almost no paint on the hood
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Unread 07-02-2013, 07:40 PM   #2
96zedjay
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1996 ZJ 
 
Join Date: Jun 2012
Location: Cincinnati, Ohio
Posts: 308
That board is the Head unit PA (power amp), the wires from the small connector marked LF RF LR RR GND ect will lead you back to the pre-amp section.
Probably on the main board... Clue to the pre-amp section will be leads coming from the EQ, Volume and Balance/Fader controls.
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Unread 07-02-2013, 08:13 PM   #3
RoldGold
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1996 ZJ 
 
Join Date: Jun 2013
Location: Philadelphia, PA
Posts: 284
The following link brings you to the thread which completes (unsuccessfully) the steps outlined in this thread. http://www.jeepforum.com/forum/f13/h.../#post15634695
__________________
1996 Grand Cherokee Limited 4.0L
PSC Steering Gear; NP249 w/ new VC; Moog TRE's, Track Bar, Stabilizer bar bushings and endlinks, control arm bushings
Still no lift, and almost no paint on the hood
RoldGold is offline   Reply With Quote




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