Dead BMW E36 Business Headunit.  - Page 1
Forum section: electronics / repair

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 05:26:04 pm
content: Hi guys.I have a head unit out of my 99 BMW M Roadster.It hasn’t worked in a few years. But I would like to attempt to diagnose and repair it.I have tried powering it up on the bench. X 12dc supplies and a ground.The unit will not power up when the power button is pushed.Any advice on where to start? I did check the pink fuse but did not open up the unit itself.Many thanks

author: fzabkar
author_rank: Super Contributor
timestamp: June 16, 2023, 06:09:27 pm
content: Quote from: magnetchief on June 16, 2023, 05:26:04 pmI would start by opening it up.

author: Kjelt
author_rank: Super Contributor
timestamp: June 16, 2023, 06:15:08 pm
content: Sent it to the repaircenter, address was on the picture

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 06:48:02 pm
content: I think you are missing the point of this group.BUt thanks....

author: kripton2035
author_rank: Super Contributor
timestamp: June 16, 2023, 06:54:30 pm
content: Quote from: fzabkar on June 16, 2023, 06:09:27 pm+1 for opening it up. and follow the +12V path while powering it.

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 07:16:14 pm
content: Ok, opened up.Will take a closer look.Was hoping someone was aware of a common fault on these 25 year old units.

author: wasedadoc
author_rank: Super Contributor
timestamp: June 16, 2023, 07:49:22 pm
content: Typical head units have two 12 Volt supply inputs. One is unswitched from the car battery to keep the station presets, tone settings and clock (time) running. The other is switched by the ignition key and provides the main power. Are you providing power to both?

author: dobsonr741
author_rank: Frequent Contributor
timestamp: June 16, 2023, 07:49:38 pm
content: I assume you have the back connector pinout. Try +12 on both Battery and Ignition, and pull up I-bus to 12V with 4.7K-ish.

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 07:56:36 pm
content: Quote from: dobsonr741 on June 16, 2023, 07:49:38 pmYes, providing power to both 12v and ground. Pins #5 & 9, then #15 to ground.

author: kripton2035
author_rank: Super Contributor
timestamp: June 16, 2023, 08:02:53 pm
content: check the output of the LM2596

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 08:03:06 pm
content: Quote from: magnetchief on June 16, 2023, 07:56:36 pmI don't believe these E36 units use i-bus.

author: magnetchief
author_rank: Contributor
timestamp: June 16, 2023, 08:06:55 pm
content: Thanks for the advice guys, will get to this over the weekend and report back.Thanks again.

author: mahi
author_rank: Regular Contributor
timestamp: June 16, 2023, 08:48:41 pm
content: Sadly there does not seem to be a true service manual with troubleshooting instructions but you can download the schematics for the BMW Business CD for free from elektrotanya.com:Download BMW Business CD (Blaupunkt CD-43 DIN) schematics

author: MathWizard
author_rank: Super Contributor
timestamp: June 17, 2023, 02:29:17 am
content: Does any current enter the CD player from your supply?Looks like some DC-DC converter and maybe linear regulators in the top right corner. And in the lower right has some stuff too. So I'd start there, look up all the datasheets for the chips, with any luck you can find there pinout, see if they have Vcc and if they are outputting anything. I find it way safer to probes chips, at connection points off the chip. So it helps to make a little map with the DMM on continuity mode 1st. SO you can probe off a cap, or resistor, that ties back to the pins. Or even solder wires on there.Then if there is power, lookup the rest if the chips, and see if they get power. Most of these chips should have enable pins, or reset pins, that can turn them on or off.I've only ever scrapped CD players/DVD players. I never had the challenge of trying to fix 1. I have a few around, and parts of them, but I've never bothered to scope them. Too busy on far easier stuff. But some day I'll try something, or even buy a broken 1, or pour salt water on 1 of mine

author: mr.fabe
author_rank: Regular Contributor
timestamp: June 17, 2023, 04:52:52 am
content: I replaced the CCC Navigation, CD, Radio, Satellite head unit for my e90. It was a much easier than trying to repair my old broken one. Found a used replacement on epray and reprogrammed the unit to work in my e90. The programming software was in German and required an old version of windows but it worked well enough to get almost all the original features back. I had to request some feature codes from a BMW group to enable some capabilities in the head unit. A replacement may be a better option for you to consider. I think I paid about $100 or less for the used part and the programming software was free...

author: mahi
author_rank: Regular Contributor
timestamp: June 17, 2023, 06:20:26 pm
content: mr.fabe:Replacing is definitely the easiest (no coding required) but this particular head unit is sought after for classic 90s BMW cars. Units in a good state still fetch premium prices (for a 30 year old head unit that does not do navigation, mp3, bluetooth,...). So it's worth trying to repair. It's an electronics forum after all.The Rover CD-43 is exactly the same head unit apart from the printing on the face (BMW owned Rover at that time) so it can be used as a donor device. If the problem is not in the display PCB, the BMW CD-43 from the E46 can be used as a donor device as well. These are typically much less in demand and can be had cheaper.

author: james_s
author_rank: Super Contributor
timestamp: June 17, 2023, 07:55:16 pm
content: The problem with stuff like this is that there is almost never any sort of schematics or proper service information available.A good place to start is hook it up on the bench and see if it's drawing any current at all, then start poking at the power section, I see at least one switching regulator in there, datasheets for those parts are available and will have example circuits likely very close if not identical to what you will find in the head unit.

author: mahi
author_rank: Regular Contributor
timestamp: June 17, 2023, 08:53:39 pm
content: james_s:I've posted a link to the schematics earlier in the thread. There is no true service manual with troubleshooting instructions, test point measurements/signals, principle of operation,... but the schematics should be quite helpful in combination with the datasheets of the parts. Naturally, if the problem is not in the power supply things may get difficult...

author: cantata.tech
author_rank: Regular Contributor
timestamp: June 18, 2023, 02:34:14 am
content: Generally speaking, the first things to go in old stereos are the capacitors.So what people tend to do is to check those first.There is a "power supply section" and it's fairly modular.You could perhaps use deduction to apply power to the unit then see if power is getting through to the front LCD board.If it's not, then you know you have a power supply issue.You'd be then checking capacitors and diodes.You might be able to look up the datasheet on particular IC's and see what their Power and Ground pins are. Then check if they are getting power.Then work backwards from there out to the power-input.There will be quite a few videos on youtube for repairing similar models.

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: June 18, 2023, 10:53:28 pm
content: Don't forget to connect the ilumination pin, otherwise the keyboard and screen backlight will be off. Check supply voltages, if ok, check reset signal, if ok check crystal oscilator.

author: magnetchief
author_rank: Contributor
timestamp: June 22, 2023, 02:50:00 pm
content: As you mention, desirable amongst the 90's BMW crowd.I'm wanting to fit this into my 98 M Roadster.Trying to keep it all original.