"Sam Smith" <unknownq RemoveThis @floatingislands.com> wrote in message
news:fq6r9f$ssn$1$8302bc10@news.demon.co.uk...
> Jeff Strickland wrote:
>> I have no clue what you are talking about ...
>
> 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.
>
>>
>> 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.
>
> 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.
>
>>
>> Me thinks the dealership will charge a handsome sum to repair this, and a
>> home remedy is really in the works.
>
> That's what I thought. 
>
>> You did not say, but do the symptoms get worse when the weather is cold?
>> This would imply any lubricant there might be freezing.
>
> 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.
>
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.
>> Stay informed about: Z4 Sat Nav Screen 
FAQ
Profile
Private Messages
Log in
