Bosch ETT 008.31 Repair Instructions page 42

Amplifier signal lies outside one of the limit values:
- With the digital multimeter (DMM), check the signal of the channel amplifier concerned at X 7 (reference point X 9) to see whether
it matches the measured value on the motherboard (at X 107, X 207 and X 307).
For performing measurements on the channel amplifiers, unscrew the analyzer part (3 screws on the back of the chopper) and
temporarily fasten it with a screw in a bore-hole in the upper edge of the device's rear wall.
!
Do not forget to replace the contact washers of the 3 screws!
- With the digital multimeter, check U
- With the digital multimeter, measure the bridge diagonal voltage of the channel amplifier in question at X 8 to X 10:
U = 0 V + 100 mV.
DC
- Measure the bridge operating point at X 8 and X 10 to X 9: U
In the event of a fault in the channel amplifier or in the stripline, replace both complete receiving chambers to Section 10.3.
- If generally low measured values are obtained at X 107, X 207 and X 307, remove the lamp and check the surface of the reflector:
if a film has formed on the lamp, clean it as described in Section 10.2.
Diagram of channel amplifiers, simplified representation
42
of the channel amplifier in question at X 12 to X 9. U
Ref
DC
= 1.0 V bis 1.4 V.
= 5 V + 10 mV.
Ref