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Discussion Starter · #1 ·
Hi, I have an aftermarket headunit and everytime I turn the key to ignition, it reboots it. I would like to make my radio stay on uninterrupted once I have the key to accessory because the reboots sometimes cause connection issues with my android auto and/or just take a really long time for the music to come back on.

I tried solving the problem using this thread here: Any way to keep the HU from restarting when starting the car
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But it didn't work like I wanted to. The headunit stays on for a good 30 seconds after I remove the key (yay!) but the headunit still reboots when turning on ignition 馃槙. I tried adding a second, larger capacitor to the 12v line that comes from the battery but it didn't change anything.

I need help because I don't understand how my capacitors can both work (when turning off) and not work (on ignition) at the same time... Could my headunit have a built-in ignition-protection feature? Even then, I wouldn't understand where the signal drop would come from as both sources are capped.

I could try to wire a relay that opens up on accessory signal from elsewhere (with my capacitors still wired in) but I feel like I need to understand this first...
 

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You might try a timed relay between the 12V and Switched 12V, so that it will keep 12V to the Switched 12V for x amount of seconds after the switched is turned off? I don't have experience with timed relays in my EE field, but it sounds like it could work. Otherwise, you'd be looking at making a whole custom circuit I think.

You may also try some supercapacitors. Be aware that most are 2.5V or something much lower than 12V, so you'd have to put some in series to get a rating OVER ~18V, ideally over 24V, as I am not sure how repeated voltage spikes affect supercaps.
 

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Discussion Starter · #3 ·
Hi, thanks for your suggestions! Since the headunit stays on for about 30 secs when I shut down the car, I would have expected my capacitors to work the same way as a timed relay... That is why I want to understand what is going on before I try other solutions. So from what I understand, the supercapacitors would act more quickly than regular ones. But if my regular capacitors are able to keep stable power when turning off, why would it not do the same during ignition?
 

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You make a good point. Didn't catch that the head unit stays on for 30 sec. because of the caps.

This must be how the head unit works. I was going to suggest that the caps backfeed into the starter when starting the engine, but then you have that diode there... Only explanation is that the headunit just does it itself. There is probably a circuit (or software) in the headunit that, for some reason, breaks the power connection to the rest of the unit (or resets it) when switching power sources. Unfortunately, doesn't sound like something you can change.
 

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Discussion Starter · #5 · (Edited)
Yes, that is what I think too. But I'm bugged as to how it does it... I have measured an uninterrupted voltage on both switched and constant 12v sources (post-cap) during ignition but the device still reboots. It's a Sony XAV-AX210 by the way. I can't figure how the headunit would be able to detect a switch from ''acc'' to ignition position and cut power internally if there isn't any voltage drop on both sides. My only guess would be that it references voltage from another source within the harness. Illumination maybe?
 

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Discussion Starter · #6 ·
I tried to contact the Sony support and ask how their radio detects key position but my question was way way too complicated for the poor guy... He said I have to ''validate my installation'' with a profesionnal before they can help me further. Funny thing is, they don't even have a list of certified technicians so I can basically ask anyone that calls himself a professionnal installer to confirm that the issue comes from the headunit and then come back for the next step.

I guess I'm gonna have to get my voltmeter and do some trial and error...

Anyway, thanks for your help!
 

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The only suggestion I have is to disconnect the ACC, and wire a timed relay/circuit with a switch to the main 12V. You get in the car, manually press the switch to turn it on, and it turns on. If you have it on without the ACC on, it will time out after, say, 30 sec. If you turn the car on, it will keep it on until you turn the car off (off off), plus 30 sec. It will require a custom circuit, or you might be able to find a timer module on Amazon or something.

Only thing is if the headunit requires both to turn on...
 

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Discussion Starter · #8 ·
Logically, that should work as much as the capacitor solution, no? The way I understand it, constant power from a capacitor fed by ACC or from a timed relay wired directly to the battery should give the same result... I think I'm going to do some testing with an extra 12v battery to try and find out what causes the reboot before going through all this re-wiring.

Gosh, it is SUCH a small frustrating detail! The capacitor mod was proposed on so many forums and I have never heard of anyone having this issue. Even when I just wired in the caps I thought it was overboard to spend so much time to solve that small of a detail. Now I feel like I can't come home empty handed after having wasted so much energy on this... 馃サ
 

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Try going back to basics. Forget about ACC+ from the car for a minute. Wire the constant (yellow) and the accessory (red) wire together, using the +12 constant from the car. Test and see if it still resets. If it does not reset, you can add a momentary on switch that you hold while starting the car. OR use a relay like this.
 
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