30BA/30BB. Repair of MSD80

Entering these error codes in Google search engine, the output is 20 .. 30 thousands of entries. And no wonder, because…

 

Related error messages:

30BA DME digital motor electronics, internal failure
30BB DME digital motor electronics, internal failure

 

For MSD80, long time MOSFET transistors of IRF644 series were used to manage the ignition coils. The Max allowed voltage of Uds is 250V, but, as real-life measurements show, the voltage (in short-term) reaches even 350 .. 380V!

How BMW allowed this “solution” to go into serial production? It’s not understandable. But one thing is clear – it is only self-explanatory, that these IRF transistors are getting damaged.

In the picture: real signal oscillogram of MSD80 ignition coil management output. Upeak reaches 350 .. 380V (probe 1:10)

 

Next conclusion – if this problem is not solved fundamentally, but the only damaged transistor is replaced (once again), itis only a question of time when the same or any other of 4/6 transistors will be damaged again. Of course, the damaged component has to be replaced, otherwise, there will be non-deletable 30BA or 30BB in the unit, but on these blocks, the snubbers have to be installed as described here. Snubbers will protect both MOSFETs and ignition coils itself.

 

What happens, if any of the ignition coil management transistors are getting damaged? MSD80 switches off one of the banks (the one, which has damaged transistor) – the engine will try to work on 2/3 cylinders (N43/N53 accordingly), MSD memory has undeletable (with active status) error message 30BA/30BB.

 

Some images, how does MSD80 management unit looks like.

In the image: upper part of top PCB: general CPU, power supply, H-bridge drivers (for management of servomotors), 6 pieces of transistors (for ignition coil management), a power switches for 12V loads PWM management.

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In the image: bottom part of top PCB: transistor drivers for ignition coils; peripheral MCU, etc. on the left and bottom PCB: management units of piezo injectors (output stages) – on the right.

 

Output cascades of ignition coil management.

MOSFET transistors of the ignition coils management. Each three (of one bank) transistors has common current measurement resistor (in green color, in the image below). If even one of the transistors is getting damaged, MSD80 is not able to measure the current, which is going thru all current bank and switches off the current bank.

 

In the image: MOSFETs of ignition coils and current measurement resistors are marked.

How to find damaged MOSFET?

Measure the resistance between its Drain and Source. If the transistor is damaged, there will be a short circuit.

 

What else has to check?

The current measurement resistor of the concrete bank has to be checked. It’s nominal 0.05 Ohm (50 mOhm). It could be damaged because, in case of this defect, high thermal power in it is emitted (above 5W);

The resistor, which is included in Gate circuit (placed on a bottom layer of PCB) has to be checked, it’s nominal 100 Ohm. If the resistor is damaged, the IC of the driver also has to be checked.

 

Replacement of transistor.

Transistors of IRF644 is recommended to replace with more modern analogs (and snubbers has to be installed in an obligatory manner, as mentioned before).

As an alternative, for example, SiHB30N60 can be used. Comparison of basic parameters is seen in the table.

As can be seen, SiHB30N60 provides higher current, significantly higher max allowed Uds (voltage), will ensure less conductive losses – it will heat less.

 

Parameters, which have to be taking in the account:

It is recommended to choose Tfall as high as possible, so at the moment, when MOSFET closes, the Uds rip-off would be as small as possible (in first few hundreds of ns). Evaluation is complicated by the fact, that for some transistors this parameter is shown by different R Gate, but a comparative picture can be obtained.

Still have to make sure, that Crss is relatively small, and the ratio of Ciss/Crss is high till Uds below 10 .. 20V. If Crss grows quickly when Uds drops down, repeated parasitic opening of transistor (if the resistor on Gate is large – 100 Ohm and in no way provides small Ugate with growing Uds, as well as – also when closing, the power transistor in this closure goes thru Miller’s area, which creates rules for parasitic oscillation in the opening/closing moment).

Also – most powerful ignition drivers from ON semiconductors can be used, for example, ISL9V5045S3ST.

 

In the image: in the repair process, looking at the PCB with a microscope.

 

In the image: damaged transistor soldered out.

 

In the image: new transistor soldered in.