Z4 Sat Nav Screen

I have had an Alpina Roadster S Lux since new for almost 3 years now. It has been an outstanding vehicle save for one minor problem. The Satnav screen seems to have problems popping up. Sometimes I have to press the
button several times to make it work and then it may only go half way.
Oddly - if it does work then it works perfectly for the rest of the drive. If I stop the car and start again it has the same problem.
Also - it seems to be getting worse as time goes on.
Has anyone else with the flip-up sat nav screen had this problem and if so is there any fix save me taking it back to the dealer for a replacement? I believe that the 1 series and the X3 also has this type of display so may have similar problems.
TIA
--
Sam

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I have no clue what you are talking about ...
Having said that, it sounds as if there is a lubrication issue with the slide mechanism. Not knowing how the mechanism works, or even what it looks like, I would try a dab of lithium (white grease) along the track and spread it around. Operate the screen a few times, then wipe the excess off with a tissue.
Me thinks the dealership will charge a handsome sum to repair this, and a home remedy is really in the works.
By your description, the screen works similarly to the tray on a CD/DVD, and gets stuck. To grease it up, you'll have to open it, remove power and push it part way closed then let it push itself open again by the spring pressure. Repeat a few times as needed, then wipe the excess.
You did not say, but do the symptoms get worse when the weather is cold? This would imply any lubricant there might be freezing.

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Jeff Strickland wrote:

I guess you have to see a Z4/X3/1 Series sat nav screen to understand it fully. There is a picture of one from a 1 series here:
http://www.webwombat.com.au/motoring/images/bmw-120i-4.jpg
You can see it just at the top.

I don't think it is sticking as the edges of the screen that move don't actually touch anything - it is purely an internal motor that moves the screen up or back again.
I just wondered if I was the only one that had the problem and that if any other long term Z4 owners had noticed it.

That's what I thought. ;)

No - it doesn't make any difference how cold/warm it is as it appears to be a motor issue. The only thing that I can find is that on the BMW internal documents for the SatNav software some mention is made as to problems with the screen opening only half-way. This is weird as they say that the software update can fix this. I'm not sure how a software update fixes a motor. The updated software doesn't fix it btw.
--
Sam

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Assume for a moment that the motor is a Stepper Motor, not a straight DC motor. A stepper motor is driven via software in that the duration of the pulses, and perhaps the amplitude, is driven by logic. Instead of a DC motor that is simply turned on, a stepper motor is given a series of pulses. One pulse results in a fraction of a mm of movement, another pulse, and another, until the movement is complete. A typical stepper motor will be driven for n pulses then stop. If any of the movement along the way did not take place, the result will be that the thing being driven will stop short of its intended destination. On the return, there is typically a Home Switch that defines the start point in concrete terms, so the closing of the device is driven until the home switch is activated.
So, when you activate the system, the screen is driven for a certain number of pulses then stops. It is not always in the right place, so they rewrite the software to make the pulse longer and/or stronger, so any minor mechanical issue will not cause a pulse to be missed. They can also write in code that says to drive the motor until the current rises as a result of hitting a physical stop. Indeed, they could have the code written to look for a physical stop already, but the current spec is too low and a false stop, or binding, can appear to be the end of the journey for the screen. In the mean time, since the screen is in the wrong place, it would over-drive on closing unless it activated a switch when it got to its home position. I suspect the closing is governed by a switch, and they drive the current higher on the reverse to make sure the screen closes fully -- this would explain why the screen closes but does not open fully.
Let's say there is a spec for a clearance somewhere. The mechanics are within the spec, but +/- spec of the slide parts is causing a tighter than expected fit resulting in the drive from the software is insufficient. They can fiddle with the software to affect the neccessary change. I suspect the software (firmware, actually) engineers simply did not write the code for the strength of the motor. They under-engineered the pulse width they needed to get the job done. The problem probably comes from the maker of the system that BMW bought and installed in your car, it is not symptomatic of BMW at all.
After all of that, have you had the software upgrade AND still have the problem? Your symptom set seems to match the problem identified in the service bulletin.
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Jeff Strickland wrote:

Wow. Thanks for the detailed info. I can only agree with you completely as everything you have described here would fit in with how my motor is working and makes perfect sense. Also there is a button on the left of the screen which if you tap it moves the screen up or down in single step increments which further supports your pulse motor description. This also works intermittently.

Yes. After I read the service bulletin I was quite excited that I may have solved the problem - but it doesn't make it any better. Over time it is definitely getting worse which leads me to believe that somehow the current is getting weaker although occasionally it works fine.
Faulty connection to the motor perhaps?
--
Sam

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Sam Smith wrote:

You know I think that it was just a case of lack of use. I have been actively using the screen each day and the problem is almost cleared. It is worse on first start-up which leads me to believe that the gears inside just need some lubrication.
The more I use it the more it seems to get better. Even though I have had the car for nearly 3 years I rarely use the screen - so it all appears to be down to lack of use.
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Here is a better picture: http://www.bimmernav.com/bmw_Z_series_bluetooth_retrofit.html
--
Sam

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