Michael7S

The Mark Levinson amp in my 2007 RX400H died immediately after replacing the 12V battery.
Well, actually it worked well after replacing the battery on the first startup of the car (and sounded great all the way home). But on subsequent 'key on' it would not deliver sound.

While reading forum posts, diagnosing, confirming power, fuses, connector integrity, etc. a funny thing happened. If the battery or the amp is disconnected then reconnected, the amp will work wonderfully on first 'key on' power. But turn the key off and then on any future power on, it won't amplify.

So after reading every possible post on the Mark Levinson Amp here in Club Lexus, I deduced that it was better to replace the amp with a 'working one'.

Got a nice clean one, with a guarantee as working, put it in, and guess what? It sounded great! Turn the key off, then back on, and, same as the prior amp. No more sound.

The amp model is 86280-0E010 and both the original and the used replacement are impeccably clean, show no signs of sitting in water etc. The replacement has blue anti-tamper paint on all the important hardware. I opened up the original amp and the soldering is lovely, and coated with some oxidization-proof coating. All caps looked fine. All solder joints looked great. I resoldered some anyway, and cleaned the already spotless connectors and bent them all slightly to ensure extra good connections. Put it in, and it worked great. Until the next power up. This and the replacement amp do the same thing. If I disconnect either the battery or the amp from the car. It'll work well on the next power up. But not after that.

The RX400H is in immaculate shape, always parked in the garage, no leaks or signs of corrosion. All stock. All systems working well. The head unit is a Jensen CAR710W installed December 2022 and works great. If I turn the Jensen up all the way I can just hear it's output through the speakers.

I can't assume that both amps have the exact same problem. So it's likely it's elsewhere in the car. It's hard to imagine that changing the battery correlated at the same minute with a connector chafing or a bad speaker (common causes of ML amp 'shutdown'), I'm ready to start tearing into ... where? Buy a third amp?

What would you check next as a failure point?

Margate330

Hi Michael78,

Ok, the thing that sets off a red flag for me is exactly what you said and I believe you are on the right track.

You already replaced the amp with a supposed "known good" and this is a good troubleshooting technique that saves lots of time.

If you trust the replacement as good, the amp is not the problem as you already suspect.

Moving on, who installed the aftermarket deck?

What was used for an interface from the deck to the amp?

Another words, as we know, the aftermarket deck is not directly plug and play with the amps proprietary protocol so what is the man in the middle?

That's where I'd start if it was me.

If you need wiring, let me know the year and I'll see what I have.

Michael7S

Thank you. Well, it's like a "Star Trek Meeting" where everyone is in agreement I called Crutchfield who supplied the Jensen and the interface to the Lexus. First off Crutchfield is an amazing company, with lifetime tech support. Instead of just blaming something else, they just dove in to help diagnose. They mentioned that the head unit is unlikely to be causing a problem, but it could be in the interface components. They suggested I disconnect and reconnect an "Axxess" box that is part of the interface and report back what happened. Each time I re-attached the Axxess interface box, the amp came back to life for a few seconds.

Based on the results they offered to send another Axxess box. Will update once I install it.

Margate330

Cool deal.

Please let us know how it goes.

It's been a while since I've looked into the amp schematics so I can't remember if there is an amp "enable" wire. If I have time this weekend I will dig in and see.

What year is your car?

Michael7S

The car is a 2007. Here is what Axxess tech support said:

1. The power-on signal to the power amplifier is a digital signal and not a 12v signal. It comes from the car's BCM (Body control module?).
2. If the BCM, after being reset, can't see the factory stereo, it won't support operation of the power amplifier. It is unknown if there is a way to mimic the factory stereo.
3. The only known solution is to put the factory stereo back in to 'teach' the BCM that there is a good stereo in there. This is most likely to 'stick' and upon swapping the Jensen/Axxess system back in, all 'should work' until the next battery swap.

I had tried to give away the factory head unit for several months and finally tossed it in the trash. Just ordered another one from Ebay for $400.

It'll be here in a week or so and I'll let you know how it goes.

Michael7S

And fixed. TLDR: The 2007 RX400H Lexus BCM needs to see the OEM stereo at least once after a hard reset to allow an aftermarket head to turn on the power amp.

Details: The Axxess tech support folks were correct. Here's what we think happened:

1. When the 12v battery was changed, the BCM (Body Control Module) experienced a reset. This caused it to reboot, which in turn tells it to 'hunt' for some proprietary signal that only the OEM stereo sends.
2. My aftermarket Jensen head unit does have an Axxess conversion box that takes care of 'everyday' Lexus/Toyota specific signals to turn on the power amp, but it does not feature the signal that 'pretends' to be the OEM stereo when the BCM recovers from a hard reset.
3. So since the BCM could not find an OEM stereo, it refused to send a signal to the Mark Levinson power amp (both my original and the replacement amd)
4. I had disposed of the original factory stereo (after trying to give it away for months). So I bought another one on Ebay for $380, plugged it in and turned on the key. All worked perfectly. The rebooted BCM was convinced there was an OEM stereo installed.
5. With the key on, I turned the OEM stereo off (volume ****) and swapped the two larger plugs back to my Jensen/Axess system. All now work perfectly.

So I'll keep the OEM head unit around in case this happens again. I'll list my original working amp on Ebay so someone else can benefit if they lose their amp.

Two takeaways: Crutchfield support is awesome. They sent me an $86 Axxess box next-day-air without question - simply to help me diagnose what the problem was.
And Axxess tech support is very knowledgeable. About 30 seconds to convey the most likely problem.

Hope this helps others.