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from a radio parts supplier. Refer to the schematic diagrams
for information regarding specific circuits. IC sockets are
used to facilitate easy removal and replacement of any
Integrated Circuit, should this ever become necessary.
Each unit is “burned in” for a minimum of 5 days before
Q.C. testing and packaging. This ensures that the MOD V
purchased by the customer will be free of defect. However,
in the event of a failure of one or more functions of the
MOD V, a service call will result by the owner. Before call-
ing the unit defective, always check for obvious causes of
the symptoms first:
1. Is the unit receiving AC. power? (Control panel lit.)
2. Has the power supply fuse blown? (Replace with
applicable fuse type and rating.)
3. Are all controls in their normal operating mode?
4. Is the supporting equipment functioning properly?
(Amplifiers, equalizers, exciter lamp supply, etc.)
When all symptoms point to an internal problem, your only
choice is to substitute with a spare (or similar piece of
equipment) and have the unit fixed by SMART Devices or
another competent repair facility.
TROUBLESHOOTING:
A quick check of the power supply voltages will indicate if
the power supply is operating properly. Place your service
meter negative lead on a convenient GROUND point (such
as a terminal strip ground). Switch your voltmeter to the
PLUS 30 volt DC range or higher and measure the positive
voltage input at the power supply terminal on the MOD V.
It should be 20 volts DC. Now measure the negative voltage
from the power supply. It should be -20 volts DC. If you
cannot obtain the voltages mentioned, you may have a
shorted connecting cable or a bad power supply.
Disconnect the low voltage cable by unplugging the power
plug at the processor end and make the tests again on the
power supply terminals. BE CAREFUL NOT TO SHORT
THE PINS ON THE POWER SUPPLY TERMINALS
WHILE MAKING THESE TESTS. A MOMENTARY
SHORT COULD PRODUCE A DANGEROUS SPARK
BEFORE THE SUPPLY GOES INTO SELF-PROTECT.
When you are satisfied that the voltages are correct, go to
the schematic diagram and study the circuit layout. The
most practical way to troubleshoot audio circuits is through
signal tracing. Put an audio signal into the input and follow
the signal with a scope until the signal stops. This method
allows you to locate a defective component in the related
section.
Since the MOD V uses a bi-polar supply, each audio IC
opamp output should measure nearly 0 volts DC with no
signal. That is, you should be able to probe each output pin
with your service meter and see a minimum DC offset. If
the opamp is showing a few volts at the output pin, it is like-
ly that a bad capacitor or resistor is causing an input bias
that forces the output of the amplifier to shift. A defective
IC could also be the culprit. Note: SOME OF THE IC’s
OPERATE ON A SINGLE-ENDED SUPPLY. These chips
get their current from the positive supply rail with a ground
return. Single-ended chips may show a very large offset
voltage at their outputs. Also check for a hairline short in
the PC card foil traces. Here are several tips that will aid in
troubleshooting:
1. Make sure the switches are in the proper position
before testing the unit.
2. Very hot IC’s usually indicate an internal short.
3. An open resistor may lead you to believe that an IC
is defective. Use a substitute device to see if the prob-
lem is in the device itself or elsewhere.
4. Shorted input capacitors may bias an IC opamp OFF.
5. Be sure IC’s are firmly in their sockets. They can be
vibrated loose during shipment.
The following paragraph applies to earlier units equipped
with the analog time delay card — MOD2X335:
Signal tracing procedures may also be employed when ser-
vicing the time delay portion of the SURROUND CHAN-
NEL(s). A signal at the input, through the filter circuit, the
delay chip, and the anti-alias filter will reveal where the sig-
nal has stopped. Refer to the schematic for pin identification
of the signal flow. The HFE4047 clock associated with the
delay chip must be operating properly for the audio signal to
pass through the delay chip. An oscilloscope will reveal
high level square wave pulses on pins 10 and 11 of the 4047
when this device is operating. If either phase of the clock
fails, no audio can pass. We suggest you NOT REMOVE
the delay chip itself unless you are positive it has failed.
This component is very expensive and can be easily
destroyed by stray static caused by handling. The BIAS pots
near the chips are factory set to each individual chip, and
should not be moved unless the IC must be replaced by a
new device.
The MATRIX CARD and NOISE REDUCTION CARDS
in the MOD V contain many components and IC’s that are
factory calibrated. The Matrix Card is not intended to be
serviced without special test equipment and test fixtures. A
defective card may be exchanged with a new one from the
factory. We do suggest, though, that the MOD V be
returned to the factory for servicing if a failure is verified.
An important part of any pre-service call is to make sure
that the operator or other theater personnel is fully familiar
with the operation of this equipment. Often service calls are
The MOD V Power Supply should be the first item checked
when troubleshooting the MOD V system.
