RMT200 Tear-Down and Modifications Thread

[15Michaeljoseph]

I'm loving this project... I thought i was BA for putting amber LED's in my old unit... This is INSANE! :)


--Mike

[17sd]

Great work!

[bmwman91]

It has been quite a while since I last updated this thread! The project is far from dead, and it is in fact 95% done. Over the last couple of days, I got my first board installed and tested. I discovered a couple of improvements that completely eliminate any clicks/pops/thumps during power on/off (which was a non-negotiable requirement I set for myself at the start), and thankfully the PCBs I have can be modified with an X-Acto knife and a little bit of jumper wire.

The little spots where I scraped the soldermask off and sliced the traces are not super pretty, but this is pretty typical for a PCB "patch" job. None of the affected traces are in the audio signal path. The board in the picture was not done/assembled yet.


When I first tested out the board in my RMT200, I found that it was perfectly silent during power on, but I would get a little thump noise when the unit was powering off. After some probing with an oscilloscope and a little thinking with a cold beer, I came up with a solution. There is another signal on the RMT200 motherboard that turns off ~40 milliseconds before the internal 12V rail turns off (and that 12V rail is what powers the opamp which makes a thump when power goes off). So, that other signal was tapped into and is now used to switch the output relays' coils. Zero pops, clicks or thumps when the unit turns off now! There is also a ~2 second delay after powering on until audio output is enabled, which is plenty of time to ensure that everything has stabilized (and the RMT200 takes 5+ seconds to boot up anyway).

I carefully checked for noises at power on/off with my old Denon headphones and there is nothing detectable now. I was also able to test the audio quality, and this thing sounds CLEAN. Even though the nice pre-amp grade opamp I am using is not really intended to drive any sort of load, it can drive my headphones to a reasonable level and the audio quality is superb. The next test will be to hook this thing up to my crazy floor-stander speakers at home (those were a heck of a project on their own).


Now that I have the little kinks worked out, I am starting to put 9 more of these together since it sounds like a few other RMT200 owners might be interested. I am also looking into adapting these to the CD43 since it could definitely stand to have a clean pre-amp output. I know how badly we all want an OEM-looking head unit with at least a few nice features!


And of course, last but not least, I have to make sure that this thing blends in with the dashboard at night. I swapped out all of the faceplate LEDs with 605nm orange ones. In a dark room, the color and brightness look like they will perfectly complement the E30 interior. Take the photo with a grain of salt...camera white balance is a pain to get right with LEDs, and to the human eye everything on there looks nice and E30-orange! I did a faceplate LED swap like 8 years ago and had to fart around with all of the resistors to get the brightness right. This time around, I had a better idea of what to look for on Digikey and I think I picked the LED's properly so that I will not have to change any resistors. We'll see once I get this into the car!

[AndrewBird]

Amazing work!

[bmwman91]

A couple more quick updates...

For those that want to know how to get a switched 12V output for the antenna & amps, just install a little ferrite bead (Digikey PN 445-1557-1-ND) in the empty spot for HB502. Doing this will make a 12V switched signal available on pin #2 of the power connector on the back (there is no wire there so you would need to buy a terminal and install it in the connector).


Also, if you want to have one less wire to connect inside the dashboard, you can jump the SAFE pin on the bottom of the motherboard to the ACC (switched 12V) pin. The SAFE security thing only trips if you try to turn the unit on without 12V on the SAFE pin, which is why it is fine to have it connected to the switched power pin. The constant 12V pin would work too, but I am not sure if the SAFE pin draws any current and I am not interested in a dead battery!

Yes, the board looks pretty torn up around those pins. I removed the whole output daughterboard when I was working some things out and it ripped a few pads off. Thankfully, everything still works!

[StereoInstaller1]

Sweet! I still have one of these waiting for you, and I still want to talk about the preamp board, give me a call sometime when you can

[Dirtboy]

I am also looking into adapting these to the CD43 since it could definitely stand to have a clean pre-amp output. I know how badly we all want an OEM-looking head unit with at least a few nice features!

If you do one for the CD43, you think you could do one for the C43 as well? Or are their innards somewhat the same?

[bmwman91]

Luke, will do, I'll give you a ring this week.

As for the CD43, this board will work fine electrically but physically it doesn't look like a good fit. It's easy enough to design another board. I am not familiar with the C43 but I bet the electronics are about the same as every other head unit, which means my board should work fine.

[StereoInstaller1]

Yes, please? I get so many customers asking for a system based on a stock deck, and they are just absolute crap.

Save them, William!

[bmwman91]

I just wish that the RMT-200 had not gone out of production (or whatever happened) since I have 9 boards 95% done and ready to roll. The RMT-200 is, hands-down, the best looking OEM'ish deck I have ever seen that can be used in an E30 while providing modern features. With the LED swap, it is ridiculous how good it looks in the car at night. The chrome bits are OK during the day, and I think that some carefully applied matte or satin black paint could completely solve that. Anyway, hopefully this unit will be stocked again at some point!

If nothing else, this is a positive trial run for my pre-amp board idea, and it would not be too hard to make an equivalent one for the CD43. Since the CD43 is much more widely used in the BMW community, there might be more opportunity there to provide people with a solid pre-amp output solution. Although the CD43 lacks modern features, a hi-fi grade pre-amp output could probably breathe a lot of new life into it. GROM Aux and BT inputs are out there too, which also help to make it a more versatile unit.

Have a good weekend. Happy Memorial Day.

[BlackSpeed66]

Very neat to see this progressing! I'm still fairly happy with the unit in my car but what you've got here would certainly bring it up a notch (or 5!)

Hoping to delve back into it once I make sure my motor swap is running properly.

[hgrunt002]

This project is amazing! It's something I'd love to do, but my resources are a little scarce and pointed at other things at the moment.

If anyone following this thread is interested in picking up an RMT200 for a reasonable amount of money, I found a european eBay seller who's got a few in stock for US$250. I contacted him regarding shipping to US, and he will do it for 35 Euro.

http://www.ebay.com/itm/181705773419?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[StereoInstaller1]

AFAIK, the CD43 is a turd, I would rather have BT, Aux and USB in a C33...plus, the E24.E28 and E30 Purists...dammit man, call me now! So much in my half baked head, I am convinced we can make the stock buttons control Bluetooth, even with steering wheel controls...

[bmwman91]

I was poking around in my RMT200 today and came up with a couple more mods.

1) USB charging from the rear of the unit. While the rear USB's data pins are not connected internally, the 5V and ground lines are. I mocked up a USB cable connection on there and was able to bring my Galaxy S3 phone from 60% to 76% in ~20 minutes, so it is definitely a high current connection. I have some fresh terminals for the plastic plug housing on order, so I will be able to make proper USB charging cables. This means that a dedicated phone charger can be available that involves NO wires in front of the dash!

2) Rear AUX input. I'll need to wait until the terminals and a 4-wire 3.5mm audio cable arrive to test this, but I am 95% sure that the rear AUX input is fully functional. Again, this would allow for an AUX input to be stashed in the glove box, so that eliminates another cable in the cockpit which keeps things looking nice.

If people that are interested in some of these mods want these, it will be $25 each, or $45 for both. Anyway, I do need to make sure that the rear AUX input actually works though lol. It'll be a week until I know since I am waiting for parts.

[Schnitzer318is]

Subbing for awesomeness... you (and the discontinued production) just increased the value of used RMT200's by a factor of 5 I'd guess.