The service manuel is very helpful, we where able to restore the device to its working operation again.
Text excerpt from page 11 (click to view)
AUDI / CQ-LA1923L
8 ALIGNMENT INSTRUCTIONS
8.1. Alignment Conditions
· Balance, Fader Control : center · Power Supply Voltage : DC13.2V · Output Impedance : 4� · Output Power : 0.5W Note : Do not align the FM/AM package block. When the package block is necessary, it will be supplied already aligned at the factory. · Bass, Treble Control : Center · Dolby NR: OFF
8.2.
Step (1) (2)
Dolby NR Alignment
Alignment Item DOLBY NR Rch DOLBY NR Lch Test Tape RFKZ0038 RFKZ0038 VTVM Connection TP7 TP6 Adjust VR201 VR301 Remarks Adjust for 388mV ±0.5dB Adjust for 388mV ±0.5dB