Table of Contents
Advertisement
6.5
OSCILLATOR TROUBLESHOOTING HINTS
As
a
the
rule
representatives
circuitry
is
troubleshoot in the field using a DVM.
may be checked at specific IC's on the oscillator
output pins may be checked for "relative" output level. In
instance relative refers to an estimated voltage output dependent
on
the
frequency
circuitry measures its input signal.
0 Vdc to
Vdc square wave with a
5
should measure
2.5
indicate steady state output.
VRS would be normal and an ac reading of 0 V would
2.5
steady
state.
the
presence or absence of signal flow.
can sometimes point to open connections, defective amplifiers and
switches, or other hardware failures.
The most effective way to troubleshoot the oscillator is with an
oscilloscope.
sinewave or square wave.
obvious and signal level may be observed at the same time.
The
oscillator circuit is located on the Analog Board
#1.
The oscillator output is routed to the attenuator
via
the
Filter
routes
the
appropriate
circuit.
This signal is either the oscillator output Band
filtered (BP), Low Pass filtered (LP), or a test
The
antialliasing
clock input prior to filtering.
If the oscillator circuit is non-functional verify that the square
wave clock signal is present at U511 - pin 10.
square
VRMS)
(2.5
indicated
on the front panel.
filter
U203 pin - 7 should be a square wave with
and its voltage swing should be approximately -3.5 V to +3.5
The output of the Switched Capacitor filter
(2.5 VRMS).
be a clean undistorted sinewave with a voltage swing of -5 Vdc to
+5 Vdc (2.5 VRMS).
6.6
TROUBLESHOOTING THE PROCESSOR (U503)
There are some processor related problems that can be repaired in
the field.
The processor on the audiometer board is a multi-
combination
device.
converter, RAM, watch dog circuitry, Priority Interrupt function,
and a free running timer.
associated as lock-ups.
shorted or loaded address or data line will stop the processors
execution process, the result is a 'lock-up'.
the processor will generally continue to strobe the address and
only
test
is a Digital Volt Meter (DVM).
generally
difficult, if
selected and the speed at
Vdc.
A measurement of
Likewise an ac RMS measurement of
This type of information allows us to
The ocsilloscope enables visualization of the
Distortion or frequency errors become
Multiplexer (U 200).
signal to the input of
filters round the edges of
which should be the
wave
It has its own internal EEPROM, D/A
Processor errors are generally
Lock-ups occur for various reasons. A
equipment
carried
not
Various power supply pins
Generally when measuring a
duty cycle the dc voltage
50/50
Vdc or<1 Vdc
>4
Using this
The
Filter
same
the
The output of
by
service
The
oscillator
impossible to
circuit
and
this
which
the
DVM's
would
indicate
check
for
information
Schematic
circuitry
Multiplexer
the
attenuator
Pass
signal
input.
the
square
wave
This is a
Vdc
O-5
frequency as
antialliasing
rounded
edges
Vdc
should
When this occurs
Hide quick links:
Advertisement
Table of Contents
Troubleshooting
