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Subject: <ALL> No Tunes When Braking

Jonathon Selig <[email protected]> said:

> I related a problem with a newly installed aftermarket Blaupunkt 
> casette/receiver in my '87 535is.  Several other digester's responded 
> that their 535's also lost switched power when the brake lights 
> are actuated.

and Ken <[email protected]> said:

> a problem with the Denon units at the time with exactly this problem 
> in BMWs of comparable vintage (c. 84-87).  Our findings were that 
> briefly (under braking) there would be a voltage drop that could 
> momentarily ... drop as low as 8 volts.  We never tried to determine 
> why the voltage drop occured, figuring that the fact that it occured 
> was enough reason to make the product compatible. 

Same thing happened for the same reason to a circa '90 Sony receiver 
in my '79 E12 528i, so perhaps brake light induced voltage dip is a 
common problem on BMWs.  This is easily cured by switching a stiffer 
power source to the radio through the contacts of a relay whose coil 
is powered by the dippy circuit.  (12-volt relays typically drop out 
around 6 volts.)

One of the important and non-trivial aspects of designing electronic 
equipment is ensuring proper operation during rising, falling, and 
(worse) intermediate levels of power.  Any company producing products 
for the hostile electrical systems of automobiles ought to know better.  
Too bad the other radio manufacturers didn't follow Denon's responsible 
approach.

Curt Ingraham
[email protected]