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Old 01-19-2013, 05:06 AM
stuartjohn24 stuartjohn24 is offline
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Location: Chippenham, Wiltshire, UK
Join Date: May 2011
Posts: 828
Mein Auto: BMW F01
T1, T2, T3 and T8 appear to form part of a protection circuit, I'm sot sure exactly, I haven't been clever enough to work it out yet, analogue electronics is not my expertise!

The circuit is connected to the MOSFET's on the output stage by the main connector.

The amplifier card receives pre-amplified analog audio from the processor card via the ribbon cable.

I have powered the amplifier card up without the processor card and it fires up OK when pin 15 is pulled low, all looking good.

However connecting the processor card it seems to be powered up all the time! Measuring pin 15 and its pulled low all the time.

Inspecting the processor card pin 15 is pulled low by the circuit highlighted and labeled '7' in the image below:

Circuit - Description
1 - 4 channel digital to analogue audio converter, this surprisingly only appears to be controlling/decoding the center speaker! audio wise anyway.
2 - 4 channel digital to analogue audio converter, also appears to be controlling the fibre interface.
3+4 - EEPROM
5+6 - Static RAM
7 - 'Wake Up' circuit and schmitt trigger inverter, possibly to filter MOST data and send to processor (2)
8 - DSP (Digital signal processor) this performs the decoding of the digital audio data to determine which channel the sound comes from.
9 - System clock circuit, this generates the timing for all three processors.
10 - This is a DC-DC voltage converter, it supplies + and - supplies to the pre-amplifiers 12 and 13.
11 - Watchdog and brown-out supervisor IC, this is the IC resetting the processors every 1.2 seconds.
12 - Audio pre-amplifier, IC on the right is the pre-amp for the subwoofers, the IC on the left is the pre-amp for the rear door speakers.
13 - Audio pre amplifier for the center speaker.
14 - I2C serial EEPROM, My guess is this stores the current equaliser settings that you set using the idrive.

The IC next to 14, is an I2C temperature sensor, its output drives the fan circuit on the amplifier card. The fan circuit is a mess, one forum stated that the fan speed increases with volume, I cant see that being the case, the advised fix if this is faulty tells you to fit entirely the wrong type/gender transistor!


The circuit was covered in a green sticky glue, I removed that and immediately smelled something burned!

I found the transistor labeled '1BW' looking a bit crispy, this is the transistor that pulls pin 15 to ground to switch the amplifier on when it receives the optical data.

The transistor was short causing the amplifier to be powered all the time, this may be why the idrive wouldn't shut down when the key was removed and kept the car awake!

It looks as though some over voltage or surge condition has occurred and damaged a number of components/circuits on both boards. Im still hopeful this can be repaired!

Anyway I replaced the transistor and the amp now shuts down and powers up only when light is present at the fibre connector.

Processor is still resetting every second or so when powered up. Interesting, when running the processor card from only 5V and 3.3V it seems to work OK and the processors are running.

I suspect some feedback from the amplifier card is shutting it down or there is something up with the 12V rail on the processor card.


Last edited by stuartjohn24; 01-19-2013 at 11:55 AM.
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