Bimmerfest - BMW Forums - View Single Post - Here are logic 7 repair instructions for every 1
View Single Post
Old 01-19-2013, 04:21 AM
stuartjohn24 stuartjohn24 is offline
Officially Welcomed to the 'Fest
Location: Chippenham, Wiltshire, UK
Join Date: May 2011
Posts: 828
Mein Auto: BMW F01
Hi Paper,

Yeah I will try and get hold of an old CAS or working LM, I guess he's using the CAS to 'wake' modules. I just send the terminal status CAN message using an arduino and CAN shield.

Anyway, I am still working on this! I have been busy reverse engineering the amplifier card to try and work out what has failed.

Here is the schematic I have drawn of the power supply and control part of the amplifier card:

It roughly works like this:

Constant battery voltage regardless of ignition status is present at T1, Q1 and pin 2 of the ribbon cable connector.

When the optical bus is woken, the previous module transmits light to the amplifier, the circuit on the processor card 'wakes' the amplifier (more on that later) by pulling pin 15 of the ribbon cable connector to ground/0V.

When this happens T5 switches battery voltage through two resistors (R14 & R17) and to the zener diode D3 which regulates the voltage to 10V. This now switches on Q1 the main power MOSFET.

Q1 now switches on and the output quickly tries to reach the battery voltage, however D2 starts conducting at around 5V, this switches on T6 which in turn tries to switch off Q1, this has now formed a regulator. This is what generates the 5V for the processor card.

T6 was shorted so the regulator circuit didn't work. I have replaced T6 and I now have 5.1V!

More to come...
Reply With Quote