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Need help - is my HU, Remote, or both, screwed up?


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Any guidance is much appreciated!

I have an '04 RLXI with what I think is the all stock Sony HU (CDX MP40) and cabin speakers.  It also has a JL Amp and a pair of tower speakers.

I'm looking to replace the head unit with something that has blue tooth support (thinking the Sony Mex-M70BT), but, would probably like to keep the underdash remote if it's still good.   The remote is the Sony RM-XM10 (pictured).  My problem is that I get really strange behaviour out when using the remote.  I get the wrong response from the remote buttons...and, they'll be wrong in different ways from one time to the next.

For example

I press "+vol" and the head unit cycles thru the "low mid high balance fader" selections

I press "-vol" and nothing happens

I press "disk +" and the cd skips back to the beginning of the current song

I press "disk -" and the volume turns up

I press "seek" to the right and the cd skips back to the beginning of the song

I press "seek" to the left and nothing happens

And the next time I fire up the stereo, the above buttons seem to randomly map to different responses.

Thanks for any insights!!!


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22 hours ago, minnmarker said:

Clean all the connections on both sets of plugs between HU and remote? Dielectric grease? Plug in back of the HU in all the way?

Do not use dielectric grease on electrical connections. Ever. It is an insulator not a conductor. The word dielectric gives that away. The only purpose for dielectric grease is gap filling mating insulating surfaces to shut down creepage distances to prevent electrical arcing. 

Definitely do the rest though. Very good idea. Clean the connections. Especially the power and ground wires. Check any cable crimps for oxidation as well. 

Edited by Slurpee
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Sony uses the same pulse code through the years but there are minor differences in functionality between old/new HUs & old/new remotes. I don't believe these small differences are your issue.

There are two connections with that remote. One is a multipin DIN cable for the display readout functions. The other is a 3.5mm 3-conductor cable which handles the commands, and this is the one you should be most concerned with.

The pulse code enters the HU through the hardwired connection and goes to the exact point that the IR target feeds into. If the HU faceplate functions and the IR remote (if included) functions work correctly, then the issue is likely external to the HU. External would be my guess.

Those Sony remotes will have a high incidence of failure in any case, but especially on the transom. They fail after getting wet and often starting working when they dry out. One bad remote, 'Y' cable, or extension cable, can also freeze select HU faceplate functions.  

The most common problem is with the interlock between the Sony HU or remote and the connecting 3.5mm cable. When not of the exact same design, instead of twisting and locking together there can actually be a bit of resistance that pushes the two apart and makes for a poor or partial connection. This can be corrected by trimming some of the soft molded pigtail housing away. Then you can use three zip ties to lock the two parts together. So with this info, which may or may not apply to your situation, give a very close inspection to these interconnects.

A 3.5mm 3-cond. ext. cable is a very common part (headphones, etc.), so it would be easy to plug in a substitute cable to at least eliminate that part.  

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