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[CalgaryBen]

The previous owner of my 1994 325i sedan had an aftermarket head unit installed (Pioneer DEH-P3100). While it's a nice system and works perfectly, it just doesn't look like it belongs (white LED display, etc.)... so I got ahold of an OEM radio (BMW-Alpine2 CM5901) with security code and installed it.

The problem is this: I get no audio from AM/FM/WB or cassette when the unit is powered on, while seek and other functions work. This does not have the "Mute" button, but a weather band button instead, so I don't think it's muted (also, pin 4 of the wiring harness [phone mute] is blank). This will be the case for anywhere from 30 seconds (rare) to several minutes (15-30), and even an hour, after which it suddenly comes alive and operates normally. If it's cool out, it seems to kick in sooner (1-2 minutes), and when it's warm, it could take 45-60 minutes or more.

Once it's working, if I turn the unit off (turning the volume control counter-clockwise until it clicks off) and then back on, it's equivalent to re-starting the car -- the unit is silent again, and I have to wait for it to come back to life.

I thought it was a bad head unit, so I bought another unit from eBay, only to discover the exact same symptoms. As a result, I'm thinking this is either a common problem with the CM5901, or else I have other problems in the amp. But if the latter is the case, why would the Pioneer head unit work fine, immediately on power up?

This is baffling me to no end! Any thoughts?

Thanks,
Ben

[CalgaryBen]

Okay, I've resolved my problem, and decided to post the solution in case others experience the same thing down the road.

The amp is powered by the radio, which is supposed to send out +12vdc on pin 16 of the 17-pin connector (white wire) for the amp to function. It looks like the CM5901s that I had were only giving about 10.7 vdc, which apparently was not sufficient for the amp to operate. If I momentarily supplied a good/known +12 vdc Vcc to pin 16, the audio system sprung to life. No need to keep the 12 vdc supply though; it seems to work fine with 10.7 vdc once it's "kick-started".

The solution might be to either integrate a transistor and some resistors into the wiring to perform the switching of power feed to the amp.

Ben

[PJK]

Hi Ben,

I have been pondering your problem since you posted it.

I have a thought. While the signal you mention is just a logic signal for the audio AMP (turn on) it is the power to the antenna amplifier. The antenna amplifier draws a non-trivial ammount of current so you may want to check the connections at the head unit connector and any splices due to the head unit swaps which occured before you got the car.

Phil

quote:

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Originally posted by CalgaryBen:
Okay, I've resolved my problem, and decided to post the solution in case others experience the same thing down the road.

The amp is powered by the radio, which is supposed to send out +12vdc on pin 16 of the 17-pin connector (white wire) for the amp to function. It looks like the CM5901s that I had were only giving about 10.7 vdc, which apparently was not sufficient for the amp to operate. If I momentarily supplied a good/known +12 vdc Vcc to pin 16, the audio system sprung to life. No need to keep the 12 vdc supply though; it seems to work fine with 10.7 vdc once it's "kick-started".

The solution might be to either integrate a transistor and some resistors into the wiring to perform the switching of power feed to the amp.

Ben

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