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Chapter 4: Trouble in Paradise? Analog
Common Analog Problems, Symptoms, Errors and Bad Fortune
LEDs are not lit?
The AC power cables insert deeply into the AC socket on the LS-40 power supply. It may look plugged
in but not be fully inserted.
There are 2 fuses inside the LS-40 power supply. They are the smaller European style 5x20mm glass
fuses. .125 amp slo-blo if set for 110 Vac .0625 amp slo-blo if set for 220 Vac.
The switching logic to the LS-40 is reverse logic. Closed contacts are off. Open contacts are on.
No analog audio?
The LED power supplies are shipped with the current set to minimum. Some adjustment will be
necessary.
The analog pre-amp power wiring polarity is clearly marked on the plugs. The ground MUST be
connected at both ends. It is the circuit ground. Reference zero for the bi-polar supply.
Poor quality analog audio?
The polarity of the analog channels is clearly marked on the plug. Confusion in the channels ( dialog
from the surrounds ) is usually a result of out of phase wiring.
Many systems will require that the analog reader be grounded at both ends (reader and processor) . The
opposite of the time honored convention. Some will require that the reader ground be connected to the
circuit ground connections of the processor and that the audio cable shield be connected to the hood of
the DB9 connector. The latter is a rare occurrence.
It is possible that a slight maladjustment to an LED will allow projector micro phonics to enter the analog
audio. A fine-tuning of the LED position will not only make this effect vanish but will increase the signal
level and permit the use of less current to the LED.
Some older processors will not provide the proper load to our reverse scan readers , with very odd results.
A common fix is to put a 500-ohm resistor across each pair of audio channels. This value may not be
correct for all processors with this problem.
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