Attenuator Troubleshooting Hint; Block Diagram Of Attenuator Signal Flow - Welch Allyn Grason-Stadler GSI 17 Series Service Manual

C P U
Figure 6-3:
6.4 ATTENUATOR TROUBLESHOOTING HINTS
(Refer to Figure 6-3:
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)
controlled by the processor via the latch (U501).
from the attenuator circuit is not present at the output
circuit check the following.
NOTE: Calibration data is used to update the
Assure that the
Diagnostic Mode DO.
In Diagnostic Mode DO the display will indicate a DAC
255 all bits at the latch output should equal +5 Vdc
attenuator should
should cause the DAC value to decrease and the
clockwise
level to increase.
all be low
attenuation/maximum
when the Tone Bar is ON, otherwise the latch is updated only when
the tone is presented).
V REF
V

BLOCK DIAGRAM OF ATTENUATOR SIGNAL FLOW

BLOCK DIAGRAM OF ATTENUATOR SIGNAL FLOW)
The input to the
calibration data is appropriate or
be at max attenuation.
At a DAC value of 0 the latch outputs
and the
output
gain. (The latch is updated continuously
E C ,
3
converter is
D/A
If the
latch circuit.
Turning the HL
should be at
output
routing
select
value of
and the
knob
output
should
minimum