RMT200 Tear-Down and Modifications Thread

[StereoInstaller1]

Yes, you got it right. Let's wait for blackspeed though, I don't trust my memory

[StereoInstaller1]

And iirc, it does come on with key off

[BlackSpeed66]

Oh wow..... it never occurred to me that it would work with the key out of the ignition. Namely because it does shut off when I turn off the car which is nice.

Just went out to the garage to check and sure enough, it will turn on w/ the car off.

[bmwman91]

Yeah I sort of found that out by accident. I was probing around looking for a switched 12V signal for the antenna and while turning the unit on and off the "ignition 12V" wire popped off of the power supply, but the unit still turned on.

[StereoInstaller1]

Dem crazy churmmanz! I am so excited for this I can't even tell you.

Any idea if they DSP can be reprogrammed?

[bmwman91]

I am 99.9% positive that the DSP can be reprogrammed. Unfortunately, unless someone at Clarion plans to give up a copy of the source code, there is no way I can reverse engineer the machine code into usable assembly code. So we can't count on hacking any features that way.

Other findings that I have made:
- The rear USB is actually connected in such a way as to provide 5V charging ONLY. The data lines are missing some components, and it turns out that they meet up with the PCB traces from the faceplate's USB input, so the thing is really only designed to use one USB device at a time. Still, it's nice that there is the possibility for a charger in addition to device input. The 5V regulator that powers that is a stand-alone part and it can probably provide 1.0 - 1.5A (max), although I wouldn't recommend it since it could still overheat.

- The rear analog AUX2 input is indeed a second AUX input as far as I can tell.

EDIT: UPDATE
- The rear connector pin labeled "ANT_12V" can easily be made to work. There is just one little component missing on the board, a simple RF choke (essentially a jumper that also helps to filter out really high frequency noise). All the protection diodes and filter caps are populated and ready to go. I am going to see if I can find a part on Digikey that will work, which should cost all of $0.10. I will provide instructions for that when I figure it out...but a proper switched 12V signal for the antenna/amp that comes from the rear connector block is looking pretty easy. I can also pull the PN for the little metal terminals so people can crimp one onto a wire and use the connector block properly when wiring!

[BlackSpeed66]

....may I be the first to say that soldering surface-mount components scares the Jeezus out of me! I consider myself to have fairly decent soldering skills but this is a new level of small

[bmwman91]

Ha yeah I know the feeling. I used to be wary of it, but to be honest, I find that surface mount stuff is as easy or easier than through hole. De-soldring / removing surface mount stuff is almost always easier, especially these days with lead-free solder, because it can be next to impossible to get it all out of a hole if it is in a big ground plane. Once you get to 0201 components and TSSOP type stuff with 0.65mm lead spacing and smaller, then I start to have a little trouble and magnification is mandatory.

Let's just say that my RMT200 is pretty chewed up in the corner where the big black connector is because I de-soldered that to see which traces ran under it, and it ripped some pads off along the way. I have access to pretty good rework facilities at work (high end soldering stations, binocular minroscopes, etc) so I got everything put back and connected up.

Anyway, almost all of the surface mount passives on the RMT200 are 0603 and 0805 sized, which you can do pretty easily without magnification. The ferritte chip that needs to be added to enable 12V output for the amp/antenna is 0603 size. All you'd need to install it is a soldering iron and some tweezers at a minimum. If you got some desoldering braid, you could even prep it properly first, although you don't really need to. I'll post step-by-step pictures of what I am talking about when I get there.

[StereoInstaller1]

Oh ell yes... Please double check to make sure if that remote stays live on USB, etc.

Any idears on the canbus leads? I bet vw controls would work

[StereoInstaller1]

Oh, and what would be so horrid about using Pico fuses as signal protection to run RCAs directly from the DSP, is it robust enough to get 2v to the amp?

[bmwman91]

Will do with the 12V signal. So far it stays active in FM/CD/AUX1 mode (and MW mode whatever that is). The SW1 output pin from the big amp IC goes to some other components so I think it powers some important stuff on there. Anyway, I will see if that holds true for SD card and USB modes.

Not sure about the CANBUS stuff. It is a standard protocol with plenty of info on the web. The trick will be learning the VW "handshakes", which might be available on some forum somewhere. If not I can try to find someone with a VW locally and hook up my USB logic analyzer to sniff things out.

[bmwman91]

Oh, and what would be so horrid about using Pico fuses as signal protection to run RCAs directly from the DSP, is it robust enough to get 2v to the amp?

The output from the DSP chip's DACs is ~2.6V peak-to-peak before it starts distorting/clipping. I am not sure what the current rating is on those outputs, but it is probably on the order of 10mA or less. ESD (electrostatic discharge) is a VERY common problem with RCA's because the tip makes contact before the outer grounding shell, so any static charge on the tip/signal line is going to discharge straight into whatever is on the other side. Semiconductor stuff doesn't do so well with ESD!

My current plan is to buffer the DAC output with an op-amp low-pass filter set at 20kHz with gain set to make the max output 5V*** peak-to-peak (to keep high frequency noise out of the signal that goes to the amp), and then running it through a relay at the output that will ensure a couple of things:
1) When the system is powered down, such as when connecting RCAs, there is no way that an ESD event can get to the electronics.
2) When the system is powering on and off, the pre-amp outputs will be grounded to ensure that no funny noises or pops get to the amplifier.

*** I can make this lower if you think that would be better. In your experience, what pre-amp voltage gives the most flexibility for amp tuning and good sound quality?

[StereoInstaller1]

5V is awesome, but will piss off some old crap amps like ADS and McIntosh. Love the decoupling relays, way old scroll quality and the LP filter... What slope is the filter?

[bmwman91]

5V is awesome, but will piss off some old crap amps like ADS and McIntosh. Love the decoupling relays, way old scroll quality and the LP filter... What slope is the filter?

Good to know. I can always set it to something arbitrary like 4V or 3.5V or whatever...it's just a function of resistor values. Anyway, it's not a big deal and is easy enough to adjust.

The output filter will be 2nd order Chebyshev, -12dB/Octave, 0.17dB flatness in the passband, with a cutoff frequency set at 22050Hz. This is also very similar to the DAC output filter that is in the schematic for the JVC HU I was tinkering with.

It's just to make sure that RF and other high-speed gunk does not couple into the output as a result of stuff inside the head unit...just about every amp has a similar filter on the input stage to make sure that the incoming signal can't destabilize the amp. Although stuff above 20kHz isn't audible to humans, it is possible for high frequency interference to mess with the power amp stage and cause audible noises.

I've got a relay time delay circuit designed up also. The relay will by default (unpowered) be shorting the pre-amp outputs to ground and leave them physically disconnected from the analog electronics that drive them. When power is applied, I have a ~1 second delay before it will connect the pre-amp outputs which is plenty of time for the head unit to get itself ready and avoid silly noises. When power is removed, the relay coil will be de-powered in about 20 micro-seconds, and the relay itself has a 1 millisecond disconnect time, so that should ensure that the pre-amp outputs are grounded and quiet well before the amp and head unit have a chance to make stupid noises. Relays might be old-school, but they will provide super legit protection for your equipment, and although they are probably 10x more expensive than an electronic solution, they are still not all that expensive compared to what they are protecting!

[bmwman91]

I spent some time with a multimeter and the faceplate PCB last night. Got all the backlight LED circuits traced out. It's all fairly basic and swapping in some orange LEDs should be pretty easy since the LEDs are 0805 size. Sure, not as important as the pre-amp outputs, but at least on mine I want all the lighting to look OEM at night! The only tricky part is getting the brightness right. Since I have no idea what the component specs are for the LEDs that are on there, I need to make some guesses about the brightness of the orange ones (and brightness can vary by a factor of 10 depending on the part). Like with the last faceplate I modded, I will probably pick super bright ones since you can always dime them down with higher value resistors.

When I do get it all worked out I will post up the LED PN's and faceplate schematic so that others can do the mod if they want.