Purpose:
Solicit feedback from EE, or adventurous g35 drivers on how to diagnose and fix the Clarion N28185 AC705.

The current problem my test system is facing
• Stereo intermittently turns off or does not turn on via the face plate controls (audio finisher board)
• Stereo turns on 100% of the time via the steering wheel controls but will turn off after a random amount of time.
• The amount of time it takes to turn off seems to correlate with how long/hot the unit gets but not always.
• While driving after the stereo is cycled many times sometimes it will stay on for a very long time.
• The stereo has been disassembled, CD changer disconnected and only the motherboard and faceplate connected. The same behavior is seen so the problem is in the stereo motherboard or the faceplate. Most likely stereo motherboard.

Questions
• How do I hook up the stereo to an external bench power supply such that I can test it outside of the car? It appears that the main power connector and the climate control cable need to be connected for the faceplate LEDs to light up and show “AM 830” etc.
• Is the faceplate required to turn on and test the main stereo unit?
• In general, what components tend to stop functioning on these units? The unit functioned perfectly for 10 years.
• What components would fluctuate so randomly? E.G. sometimes they work for long periods other times they don’t function at all or only for a short period of time.

I have obtained the service manual for this unit and attached it as a multipart rar archive for reference. I will post detailed pictures and procedures as the thread develops. Let’s get some public information out about how to fix these units!

 

Update:

I started reading abnormally low voltage readings off the main power supply. I suspected bad ground so I ran a ground wire directly to my battery and sure enough the stereo operates well. But only with the faceplate disconnected. If the plate is connected it still appears to be "jammed".

How do I fix the bad ground? Where does the wire run to after it leaves the harness?

Does the audio finisher board use a separate ground? Or is a more likely cause a sticky worn out button?

 

Ok I discovered the faceplate has another ground that comes in on the connector for tha AC controls. I ran a new ground to that and all appears to be working stable. For those of you that experience this problem there is a good ground right below the stereo via a screw that goes into the frame of the car.

The big question is WHY? Why did the ground suddenly stop working for both the audio power harness and the AC harness? What are the implications for the rest of the car?

 

Well it turned off once during the ride home today. So its 95% more stable but there is some sort of short happening. Does anyone know where the ground cables from the audio harness run?

 

As far as I know, the chassis of the radio just grounds directly to the bracket it mounts to.

 

looks like the whole ground thing was a fluke. It was stable for a little while but then started misbehaving again. What is weird is if I run the stereo without the faceplate attached it runs stable forever. However as soon as I attach the face plate it goes back to random. Especially when its "cold". After running it over and over it seems to stabilize. I have no idea where to even begin...

 

Maybe the ribbon cable is to blame?

https://g35driver.com/forums/audio-v...e-diy-fix.html

 

Yeah I took that cable out and tested all the leads and it seemed to be fine. I also put tape on the back of it on both sides so it would fit snug in the connector. However, maybe there is a short or something in there. Seems weird how it will work for hours, I turn it off on the bench, come back an hour later turn it back on without moving anything and the faceplate does not work or only works for a few seconds then turns the whole stereo off. Seems like a voltage regulator or some sort of protection circuit is kicking in.

I should probably just replace the whole thing with aftermarket but now its like a "thing" that I have to fix this thing.

 

This is a huge reason why I don't recommend keeping the factory radio at all once it starts to fail.

Go aftermarket and save yourself the frustration, don't throw good time after bad.

 

Just to follow up on this. I wanted to drive it around for a few weeks to make sure the "fix" worked.

After a lot of testing I could not determine if it was the head unit or the finisher board causing the issue. With the finisher board disconnected the radio functioned perfectly. However with the board connected the LED display would sometimes lock up and the buttons would become unresponsive.

As an experiment I decided to scotch tape pins 9 and 10 of the ribbon cable. These pins are the TX and RX pins that the ICUs use to set the station display etc. This had the effect of disabling the display and buttons but now the radio was stable and did not turn off. Interesting.

At that point the skills and equipment needed to trace the problem were beyond my level. I wanted the button controls back as well. So I decided to just remove the entire section of the circuit that powers the LED display. You can do this by de-soldering the transistor marked Q606. I don't know if replacing this transistor would have fixed the problem I just decided to remove it. This has the effect of disabling the 30v and 15v rails that run to the finisher board.

After hooking everything back up everything has been working flawlessly for the last few weeks. The trade off is you can no longer tell what station you are on. But all the buttons, AC controls etc work and the radio stays on.

Hopefully a EE can chime in and tell us why the hell this worked after reading the circuit diagram. I figured it out the brute force way through process of elimination.

Total cost: 0 dollars.