|bh||Becker Grand Prix 612
- Unit Log -
|Serial Number:||FR 6169846 (on label inside)|
|1983 (83xx latest component date codes)|
|Date of Receipt:||1989|
|Source:||Noticed in surplus room in rear of RP Electronics at 4th Ave. & Arbutus.|
|State upon Receipt:||Good physical condition but major component damage, presumably from reverse voltage application.|
Schematic obtained from Ralph's Radio.
|Procedure:||Installed in Datsun 710.|
|Procedure:||Removed from Datsun. Used in basement workshop.|
|Procedure:||Installed in Honda.|
AM receiver problem.
T251 faulty perhaps due to static.
Two cracks in PC board traces (390K resistor to T251-G1 connection open, input clamp diode cathode to ground connection open).
T253 moved to T251, T253 replaced with 40673. T253 voltages after replacement: drain=2.9V, source=1.8V.
|Procedure:||Schematic redrawn from manufacturer original. Microprocessor inferred to be F3870 family.|
|Procedure:||No reception on AM. U451 (TDA1046) AM receiver has odd voltages on pins, notably pin 16 which should be an internally regulated +3.3V is +7.25V. Voltages on 3 MOSFETS in AM section look quite sensible. U451 removed. Voltages on empty pins are sensible. Powering up the IC with 8V supply shows 7.3V on pin 16. Internal regulator in IC appears to have failed. Need a TDA1046.|
|Procedure:||Volume level will not go below approximately half. ULAUT is 2.16V, rather low. LAUT signal is inverse control so the low ULAUT is inhibiting the volume from going down. T453 found to have CE conductivity, replaced with 2N3904. Fixed.|
Sharp, loud pops from speakers at seemingly random intervals but rate of occurrence changes with station.
Rate increases if bass control is increased.
Scope shows bursts of tens-of-KHz oscillations emanating from U451 (TCA5500) L/R outputs.
UKLAN (voltage for tone control DA converters) is over +11V when it should be nearer to +5V.
T451 found to have CE conductivity, replaced with 2N3904.
Measurements taken for ULAUT, UKLAN, etc.
|Procedure:||Replacement TDA1046 (U451) installed. Fully functional.|
Supply current measurements performed, supply voltage = 13.5V.
Accessory off: 13 mA
Accessory on: 92 mA
Turned on, volume at minimum: 490 mA
Becker Grand Prix 612