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NVX Amp Power Issue

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
I have a question and can’t seem to find what the issue is, short of taking it back to the place I that helped me install the nvx sub and amp.

The issue started when I had the MCU died on me. When I took it in to have them look and recover the MCU1, the amp stopped to work. They then upgraded to MCU2 and the amp still has no power to it.

I opened the frunk and saw the amp power is connected to the 12V battery. I checked the NVX fuse box connected to the 12V battery abs the fuse looks intact. At the amp, when I use a power meter to it, I get no signal. At the passenger door, I removed the floor panel below the Tesla door guard and don’t see and disconnect.

Is there something supposed to connect to the back of the MCU that was not connected?


I can’t figure out where else to check where the power is loss from.

it’s a 2015 MS.

suggestion?
Thanks.
 

MikeHolliday

Member
May 9, 2020
316
207
Worthington, Ohio
Have you put a Volt Ohm Meter on the power source at the Amp or are you stating that the Amp has no power because the light is not on the Amp?

Put your Volt Ohm meter in impedance mode, disconnect the signal that coming from the MCU2 and see if the circuit is open. If you have an open circuit, then I would say that when they installed the MCU2 that they disconnected to cable and did not reconnect the cable.
 
Last edited:

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
Have you put a Volt Ohm Meter on the power source at the Amp or are you stating that the Amp has no power because the light is not on the Amp?
I used a volt meter at the amp. No power. Originally I though the amp might be bad or the fuse inside the amp was bad, but when checking the fuse inside the amp, it looked fine. Used a volt meter on the power cable connected to the amp, no power.
 

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
I checked both the large inline fuse and the fuse in the amp. I didn’t check the inline fuse with the volt meter. But I did check with a volt meter on the line right at the amp.
 

Cheburashka

Active Member
Jan 29, 2018
2,216
2,625
Los Gatos, CA
IIRC, there is a signal line that is connected to a switched 12V power source that will tell the amp to turn on.

That said, you should still have power at the amp. It's one continuous line from battery to amp, with just the fuse close to the battery being the only interrupt.

My NVX sub/amp sound amazing with MCU2.

I actually have the cables left over from the NVX kit in the garage as I used different ones. I'll take a look when I get home to see if there is an interrupt somewhere else in the wiring but I don't remember that there is.
 
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MikeHolliday

Member
May 9, 2020
316
207
Worthington, Ohio
I am not speaking of checking the 12 volt Power Cable with the Volt Ohm Meter... I am speaking of checking the Signal Cable that bring the signal to the Amp to be amplified and then outputted to your speakers.
 

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
I am not speaking of checking the 12 volt Power Cable with the Volt Ohm Meter... I am speaking of checking the Signal Cable that bring the signal to the Amp to be amplified and then outputted to your speakers.

oh, hmm I didn’t check the input cable. I only check the 12v cable that leads to the amp with the volt meter. I checked at the amp.

I will try that tomorrow to test the audio input line to see.
 

Cheburashka

Active Member
Jan 29, 2018
2,216
2,625
Los Gatos, CA
I just checked the NVX kit that I have and it's a straight wire from battery to amp with the fuse inline. Nothing fancy or special and no relays. If you have 12V at the fuse, you should have 12V at the amp.
 
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beatle

Active Member
Aug 31, 2019
1,032
502
Springfield, VA
If you're not getting anything at the amp on the fat power cable, it is disconnected from the battery at some point. Ensure you have power there before moving on to the 12v "turn on" lead. Trace the amp's ground cable as well.
 

2101Guy

Active Member
Jan 6, 2020
1,447
1,251
USA
I just checked the NVX kit that I have and it's a straight wire from battery to amp with the fuse inline. Nothing fancy or special and no relays. If you have 12V at the fuse, you should have 12V at the amp.

I did the NVX Sub/Amp install myself earlier this year, and can confirm the above.

Also, nothing at all connected directly to the MCU for the install. As noted in this thread, one main large 12v cable directly from the 12v battery to the amp itself. Then there is also a signal converter box that almost always gets installed in a open area to the left of the steering wheel behind the dash/console. That signal converter box has wires from the cars speakers so that it knows to interpret bass signals to go to the amp/subwoofer. I seem to recall that signal converter box needing a switched power signal from a smaller wire. But in my install, I never had to do anything behind the MCU and certainly did not have to connect anything there.
I did install my subs control knob (3M double face tape) in that storage area underneath the MCU. When I had my MCU2 installed, they would have had to have moved the knob temporarily, which they did. When I picked up the car the knob was in the same place, just no longer taped up. But my amp/sub still worked 100% fine with the MCU2.
 

Doanster1

Member
Feb 14, 2018
913
481
Oregon
And... you said you checked the fuses and they “looked” fine. Did you actually use the meter to see if the fuses were still good (zero ohm impedance) vs blown (open circuit/infinite impedance)? Fuses can look ok when they are intact blown. Good luck.
 
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MikeHolliday

Member
May 9, 2020
316
207
Worthington, Ohio
Absolutely, if a fuse burns or blows in the fuse "window" it is east to see, but if either end of the fuse burns through ypu generally will not see it. This is not necessarily common, but can happen. It is so easy to check the impedance with a Volt Ohm meter, it should never be over looked...
 

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
I checked again this morning. On the volt meter set at 200 on the DC test, I get initially 2.1 and it slowly drop to hover around 1.3 when I place the volt meter at the fat inline 12v and ground cable right at the amp input.
 

Doanster1

Member
Feb 14, 2018
913
481
Oregon
I checked again this morning. On the volt meter set at 200 on the DC test, I get initially 2.1 and it slowly drop to hover around 1.3 when I place the volt meter at the fat inline 12v and ground cable right at the amp input.
Put it on impedance mode (Ohm symbol) and put the leads on each side of the fuse. If you have the beep-mode on, you’ll hear a solid tone if the fuse is good. Silence if it’s blown.
If you still want to check for voltage, the near side of the fuse should still read 12v. If you’re seeing 2v when the lead is on the downstream side of the fuse then you’ve basically determined that the fuse is bad.
(Sorry if this is coming across as assuming you don’t know what to do; just trying to be clear/succinct; sorry if you’re well versed...)
 

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
Put it on impedance mode (Ohm symbol) and put the leads on each side of the fuse. If you have the beep-mode on, you’ll hear a solid tone if the fuse is good. Silence if it’s blown.
If you still want to check for voltage, the near side of the fuse should still read 12v. If you’re seeing 2v when the lead is on the downstream side of the fuse then you’ve basically determined that the fuse is bad.
(Sorry if this is coming across as assuming you don’t know what to do; just trying to be clear/succinct; sorry if you’re well versed...)
That’s. I have no idea what I am doing :) just poking around to see where the issue is.

so if I understand, check for ohm at the large fuse that is split at the 12V battery to the fuse. Do I touch the negative wire one end of that inline and positive at the other end of that fuse?
 

smilepak

Active Member
May 11, 2015
1,712
524
Eastvale, CA
Put it on impedance mode (Ohm symbol) and put the leads on each side of the fuse. If you have the beep-mode on, you’ll hear a solid tone if the fuse is good. Silence if it’s blown.
If you still want to check for voltage, the near side of the fuse should still read 12v. If you’re seeing 2v when the lead is on the downstream side of the fuse then you’ve basically determined that the fuse is bad.
(Sorry if this is coming across as assuming you don’t know what to do; just trying to be clear/succinct; sorry if you’re well versed...)
You mean that right?
FAAEF7B9-4872-400B-AF49-2BCBA896FCC1.jpeg





M
 

Doanster1

Member
Feb 14, 2018
913
481
Oregon
That’s. I have no idea what I am doing :) just poking around to see where the issue is.

so if I understand, check for ohm at the large fuse that is split at the 12V battery to the fuse. Do I touch the negative wire one end of that inline and positive at the other end of that fuse?
Yep. When checking for impedance, it doesn’t matter which end goes where. You’re only checking to see whether the circuit is whole (fuse wire hasn’t been broken) or whether it’s open (fuse did it’s job and blew to protect the amp).
So just put one lead on each side of the fuse that’s inline to the positive terminal of the battery and see what you get.
 

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