Building an AUX In with the stock CD-Player (now with pics!), See post 8 Options

[solidxsnake]

So I got sick of using a cassette adapter in my '95 Celica a while ago.. the mechanical noise of the deck as well as the tape hiss was incredibly annoying for a lot of my music.

I pulled the stereo out and checked pinouts on all the connectors online only to find there is no legitimate line-in source. I found L-R-GND pins in the 13-pin DIN socket on the back of the tape-deck head unit, but hooking wires up to it does nothing.

What I ended up doing was tapping into the line-in ports in the DIN connector by tapping into the CD-Player's line-out. This proved to be a headache at first, where what I did was tore up the CD-Player and pulled the corresponding wires from the 13-Pin DIN socket (LOut, ROut and GND) out from where they went into the CD-Player and connected to the logic board. What happened here was that, while it worked while the CD was already playing, it did not work if power was cut. When I turned the deck off and back on again, the CD player would not power up, as the headunit is expecting a specific line-in signal from the CD-Player (it's got a complex logic circuit)...

I had an epiphany yesterday, and went to work. I kept all of the wires connected to the board where they went, but instead removed some pins from the connector that connects the one logic board to the other (there are a total of 3 logic boards, the main one, the board that controls the optics/motors/mechanics, and the one with the buttons and LCD, that controls the faceplate and external interface). There is a small PCB Bridge between the main logic board and the optics board. I removed this PCB, then desoldered the pins L, R and GND from one of the connectors (you have two connectors to choose from, pick one). At this point, I soldered my L, R and GND from my AUX-In port (which I retrofitted in the faceplate, it can go anywhere really) to the main logic board. I hooked everything back up, and lo-and-behold it all worked great. Except for one small caveat, where if the optics had to pause to read the disc (for instance, a scratch in the disc, a bumpy road causing skipping, or seeking/skipping tracks), the sound from the AUX-In port would cut out. I found a wire inside labeled "MUTE."

The fix for this was to desolder one of the two pins on the bridge PCB between the main logic board and the optics board that connected the "MUTE" signal trace to both boards. And, luckily, it works flawlessly. Now I have a perfectly working AUX-In port in my stock CD player. All I need to do is press "CD" on my head unit (the CD unit, actually) and plug something into the AUX-In port I retrofitted, and I have a direct line-in into the head-unit. This MUTE wire, thus, is the wire that signals the head-unit to pause when the optical drive is either seeking the disc, or encounters a read-error.

The only problem with my method is that the CD-Player is left nonfunctional afterwards. What happens when the AUX-In is enabled is basically that the head-unit believes a CD is playing (and indeed, the CD is spinning in the CD-Drive, and the display shows a track and time, along with RPT, Scan, RAND, and other display icons), however, the audio signal it is sending isn't getting to the main logic board, and thus isn't making it to the tape-deck/head-unit, and thus isn't getting amplified or sent to the speakers. Instead, the line-level signal from the AUX-In port is sent to the tape-deck/head-unit, and is amped and sent to the speakers.

I feel as if that would be a simple fix, where you can integrate a switch on the CD-Player that controls a four-pole double-throw switch that connects the MUTE, L, R, and GND traces to their original position, or to the AUX-In port. A quick schematic would be:

CODE

To CD Player Logic-board "L" - Pole 1 Left Signal - To AUX-In port Tip/Left
To CD Player Logic-board "R" - Pole 2 Right Signal - To AUX-In port Ring/Right
To CD Player Logic-board "GND" - Pole 3 Ground - To AUX-In port Sleeve/GND
To CD Player Logic-board "MUTE" - Pole 4 Mute - Disconnected/Floating

With this schematic, you would have the stock CD Player functionality as long as the switch is flipped to the first set of throws (To CD Player Logic-board). To enable the AUX-In, start the CD Player as if you were going to play a CD, plug something into the AUX-In port, and then flip the switch, and voila, you have a line-in. Granted this is all theoretical, but I see absolutely no reason why it shouldn't work.

I'm not too worried about it as I managed to destroy the CD-Player mechanically (it doesn't eject or accept discs properly, but it will play them if I manage to work them into the drive and toy with the mechanics to lock it in and spin the disc). As long as I don't press eject, then I won't have to worry

I'll get up pics at some point. It's quite a bit of work for a measly AUX-In port, but it sure as hell beats spending money on a new head-unit for a free mod (or next to $10).

Any questions, please ask

This post has been edited by solidxsnake: Aug 14, 2009 - 9:10 PM

[DanAdamKOF]

Dude, thanks for posting this. I was toying with a few ideas as to how to add an Aux In to my factory headunit (I like the stock look, at least for now...), and it seems you've taken care of everything.

Now all I'd have to do is figure out where the appropriate points are on my CD Player headunit (seems like yours is different), and figure out where to mount everything... I was thinking of mounting them inside that under-the-radio compartment, but I'd have to reach all the way in there to mess with them. Maybe I'd mount them on the lid, right underneath the headunit... Well, I guess that's all up to me.