Lafayette lr 9090 service

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Lafayette

LR-9090'
SERVICE ADJUSTMENT PROCEDURES

These procedures have been carefully prepared to aid you in servicing the
LAFAYETTE LR-9.09.(1 AM/FM Stereo Receiver. It contains receiver adjustment.
procedures, replacement of Dial Lamps and Dial Cord Stringing.

Before servicing this receiver, read the LRagogo Owner's Manual, as it will
help you to understand the correct operation of the receiver's controls and
their functions. The Owner's Manual also contains Interior Parts Location
Drawing, PC Board Drawings and complete Schematic Diagram including voltages.
Parts Listing for this receiver is available on Microfische Film from the
Lafayette Parts Department, Hauppauge NY.

CAUTION: Only a qualified technician having enough knowledge and experience
in repair of solid state equipment should attempt to service this
receiver, or damage to the unit may result.

Please follow the procedures outlined - do not attempt short-cuts.

* Always remove the AC power cord plug from the outlet when soldering or
making repairs to the unit. Wait until the power supply filters have;
dissipated their charge.

* Do not use an ohmmeter to test transistors. In some instances the voltage
across the test probes of an ohmmeter may exceed the base to emitter break-
down voltage. Therefore, do not use an ohmmeter for testing transistors
unless you are certain of the transistor's capability.

* Do not replace a defective output transistor, until you have determined
the cause of its failure.

* When installing a power transistor, make sure that the bottom of its
mounting flange, surface of the heat sink and the insulator between them
are free of dust and dirt particles. Failure to observe this precaution
will prevent proper heat transfer and may even puncture the insulator,
causing a short circuit to ground. Also, for proper heat transfer, both
sides of the insulator should be coated with silicone grease.

* To prevent damage to the printed circuit boards and components, use the
correct soldering iron; small diameter tip for single connection, large
chisel tip for large areas and special de-soldering tip for multiple
connection component removal.

* All voltage measurements should be made with the AC line adjusted to ll7V.
VTVM DC measurements are made to chassis ground, with no signal input unless
specified otherwise. Measurements may vary plus or minus 20%.

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SERVICING NOTES

1. From a servicing stand point, the voltage drop across the emitter
resistor is very important in determining circuit operation. A
higher than normal emitter voltage would generally indicate excessive
current flow which can be caused by a shorted transistor or bias
defect. A lower than normal emitter voltage would generally indicate
an open transistor or bias defect.

2. Check the emitter voltage in each stage and compare them with the
voltages given in the circuit diagram. If the voltages obtained
are 20% higher or lower than the voltages given on the circuit diagram,
troubleshoot and find the defective component(s).

3. When servicing the receiver, you may quickly determine the circuit
operating conditions by using the method of signal tracing and
checking the waveform signal at any given stage on an oscilloscope
display.

IMPORTANT: Do not attempt to adjust any FM MPX coils if you have not

a proper MPX stereo generator. These coils generally cannot
be adjusted without an MPX stereo generator.

MAIN AMPLIFIER IDLE CURRENT ADJUSTMENT

NOTE: The following adjustments are located on PC Board PS-MAOZSCOX:

1. Set the receiver VOLUME Control to the "0" position for minimum volume,
with no input signal.

2. Connect an Ammeter in series with the collector of transistor "Ql" on
the top side of the main amplifier PC Board. The DC Ammeter should
indicate 50 mA. If not, adjust RVl, lOO ohm "Bias" adjust for 50 mA
current indication on Ammeter.

3. Repeat Step 2 for the other channel.

AM TUNER ADJUSTMENT

NOTE: The following adjustments are located on PC Board PS-TUOlQCOX
unless otherwise specified:

AM IF Adjustment

1. Set the receiver SELECTOR switch to AM.

2. Connect the output of an AM Generator to the "AM" antenna terminal
(on rear panel) and chassis ground.