Faulty Channel Amplifier - Bosch ETT 008.31 Repair Instructions

8.7

Faulty channel amplifier

Amplifier output signal outside permitted range during zero adjustment.
The MPU detects a voltage < 1.0V (lower limit) or > 3.5V (upper limit) in the measuring channel on the motherboard (X 107, X 207 or
X 307) designated by the fault number.
Diagram, circuit diagram of channel amplification, simplified representation
If sum-total error 7 (Err 1 + 2 + 4) occurs, a fault in the chopper motor or lamp is probable.
- Visually check whether the chopper motor is running (can be seen from the motor shaft). If it has failed, replace the chopper. If this
is unsuccessful, replace the "power electronics" module.
- Check the lamp resistance (remove connectors from X 6 and X 3 on the motherboard).
Cold resistance = 3o Ω + 3 %. If not, replace lamp.
- Check U on the motherboard at X 13 to X 16: U
REF
If individual errors appear, check with DMM
whether the affected amplifier output lies outside the specified limit values (reference point X 16).
Amplifier signal lies inside limit values: Fault in processing of measured values, replace motherboard.
= 5 V + 10 mV. If necessary, adjust U
REF
X 107 for Error 1
X 207 for Error 2
X 307 for Error 4
with R 12 to 5 V + 2 mV.
REF
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