DIY test of power output stage/ignition amp module N122 (long & BWW)
05-06-2012, 09:02 AM
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write up not applicable to all n122 though!!!!
Bosch released some scematics and some modules are not using JFETs, but BJTs.
So all the measurements algorithm does not apply fully. The transistors are not working as voltage controlled resistors, but cut-off/saturation (standard BJT power amplifier).
I would recommend to use the flashlight bulb/lamp method for testing and drive that to 3V and 4.5V
The described method was showing infinity resistance on all 4 channels. Reverse the polarity, some negative resistance was shown, because of DMM applied voltage and effect on the junctions. Obviousely, cyl 2 was always infinity, but that's a different story.
Tipically you need to buy multiple N122s, as you change them more frequently than the brake pads
My car had 2 N122 replaced....
So all the measurements algorithm does not apply fully. The transistors are not working as voltage controlled resistors, but cut-off/saturation (standard BJT power amplifier).
I would recommend to use the flashlight bulb/lamp method for testing and drive that to 3V and 4.5V
The described method was showing infinity resistance on all 4 channels. Reverse the polarity, some negative resistance was shown, because of DMM applied voltage and effect on the junctions. Obviousely, cyl 2 was always infinity, but that's a different story.
Tipically you need to buy multiple N122s, as you change them more frequently than the brake pads
My car had 2 N122 replaced....
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