V
REF
OSC.OUT
00X
CPU
CI
RCU\T
x
ATTE
UJuAToR
L1302
u301
L
EC,
3
ROUTIM$
V
LATCH
l-l510
D/A
-
CON’JWI’W.
-
UNEARIN
u303
ADIllS
-
u302
u300
Figure 6-3:
BLOCK DIAGRAM OF ATTENUATOR SIGNAL FLOW
6.4 ATTENUATOR TROUBLESHOOTING HINTS
(Refer to Figure 6-3:
BLOCK DIAGRAM OF ATTENUATOR SIGNAL FLOW)
Non linearity, no output,
large shifts in output level.
The VCA
(U301)
output is controlled by a dc voltage produced by
the D/A converter
(U303)
The input to the
D/A
converter is
controlled by the processor via the latch
(U501).
If the
output
from the attenuator circuit is not present at the output
routing
circuit check the following.
NOTE:
Calibration data is used to update the
latch circuit.
Assure
that the
calibration data is appropriate or
select
Diagnostic Mode DO.
In Diagnostic Mode DO the display will indicate a DAC
value of
255 all bits at the latch output should equal +5 Vdc
and the
attenuator
should
be at max attenuation.
Turning the HL
knob
clockwise
should cause the DAC value to decrease and the
output
level to increase. At a DAC value of 0 the latch outputs
should
all be
low
and the
output
should be at
minimum
attenuation/maximum
gain.
(The latch is updated continuously
when the Tone Bar is ON,
otherwise the latch is updated only when
the tone is presented).
-
50
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