Audi A4 AFN Bj97 springt nicht mehr an -> MSG kaputt ? | Posts 32+

"If it weren't for the standard Siemens C166 chip, for which you can find datasheets with pinout diagrams, I would never have figured it out. I'm not familiar with any of the other ICs. They all have Bosch part numbers, and it's practically impossible to find datasheets or functional descriptions for them."
At least, this way you have a well-known IC as a starting point for further measurements.

Following the reset line, starting from C166 (/RSTIN), the following components are connected:
- C166 (_Reset_IN = Pin 27)
- SCL4410V4 (Pin 44)
- B30279 = Philips CC212V2 (Pin 11)
- A pad for the large, unpopulated PLCC footprint.
- a pin of the TO220-5 package (the only TO220-5 on the board; after removing the heatsink clip, you can still see a Bosch number [which I've forgotten again] and a Siemens label).

By measuring the voltage drop on the reset line, I've determined that the TO220-5 must be the reset driver. It's a 5V voltage regulator (and, according to my measurements, the only 5V regulator on the board). I see 12V (U_IN), 0V (GND), 5V (U_Out), the reset output, and a fifth connection that's connected to a 100 nF capacitor. This capacitor sets the reset duration (100 nF corresponds to 25ms according to datasheets of similar Siemens voltage regulators). However, the voltage levels there were quite strange and unstable. By applying an external voltage via a potentiometer to the DelayAdjust, the reset sometimes became inactive, and the circuit came to life (PWM, bus accesses, etc.).
Since the 5V supply is stable, I assumed that only the reset circuit was faulty. So, I left that part in place and only disconnected the reset output from the rest of the circuit. Now, it's being driven by an MCP130 reset IC (SOT23-3, 4.5V, 350 ms). The reset duration is a bit longer, but I just happened to have that IC on hand.

Regarding the voltage regulator: I don't know the exact model that's installed, I simply searched for Siemens U-regulators in the same housing. That's how I found parts that might have similar specifications (TLE 4260 / TLE 4265).


Andi.

Rekord81 wrote:

Yesterday, I re-measured the MSG in detail and ultimately concluded that the reset generator, which is integrated into the 5V voltage regulator, is defective. The reset was constantly active! I then disconnected the reset line from the rest of the circuit and powered it instead via a separate reset IC.

Wow!

I also have deep respect for you for finding the error. To my knowledge, this is the first MSG in this forum that has died without external interference. It's definitely the first in the DS forum to have died without external interference and then been repaired by a private individual, including a detailed description of the error.

Also, I'm sorry for trying to distract you from MSG so often.

Regards,
Guste.

guste100 wrote:

100% certainly the first one in the DS forum that died without external influence and was then repaired by a private person, including a detailed description of the error.

@ Andi: After your excellent troubleshooting, wouldn't you like to continue being present in this forum as a "StG therapist"? *gg*

Quote:

and then repaired by a private individual, including a detailed description of the faults.

"Private individual" isn't quite right. I professionally and privately (among other things) program motor control units, and I also do some electronics work. However, I don't work in the automotive sector, so my knowledge in that area is quite limited; I have to painstakingly acquire everything myself. And for me, reverse-engineering a 4-layer MSG (Motor System Generator) circuit board without schematics or datasheets is not enjoyable. I still do it, though, because control units like those, which are sold for €1300 by unscrupulous vendors but have a material value of no more than €80, can often be repaired for just a few euros (in this case, 67 cents plus VAT). But that's the same problem with every manufacturer.

Quote:

@ Andi: Wouldn't you like to stay present in this forum as a StG therapist (after the excellent troubleshooting)? *gg*

"Thank you, but I'm fully booked until 2025. All in all, I've probably spent at least three full days dealing with this problem (including a fruitless search for spare parts at local junkyards). I usually can't afford to spend that much time on it. Privately, I only repair things that are needed in our household or that relatives bring to me. I currently have a TV, a stereo system, a dishwasher, a garden tiller, brake discs for my car, and a few other urgent items waiting to be fixed."

Best, Andi.