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5.5
PC BOARD
CLEANING
Due to very
high impedance
circuits, it may
happen
that con-
tamination on
the PC
board causes the limiter
to
perform
poorly.
Moisture, smoke or polutants
in the air
may result
in
slightly
conductive deposits which affect the operation
of Q7
due
to leakage.
Existence of contamination can be verified with
a
simple
test.
Supply
a
steady input tone
and,
with
no limiting indicated
,
adjust
the Input and Output controls to read
0
VU on the meter
.
Remove
the top and
bottom
covers from the limiter and locate Q7
.
From
close proximity, exhale deeply on the circuit board around
Q7.
The
moisture
in the
breath will induce surface
leakage, and the VU
meter will indicate
a
drop
in
output level.
If
no contamination
is
on the board, the output level will return very rapidly to
0
VU
(within
10
seconds or less).
If
contamination
is
on the PC board,
the
moisture will be retained
for
a
longer time
and
cleaning
of the
board
is
necessary.
Disconnect the power cord from the AC mains.
Prepare
a
clean-
ing
solution by mixing equal parts
of distilled
water
and
isopropyl
alcohol.
Use
a
new tooth brush
(or
similar stiff bristle brush)
and
apply the mixture
to the
circuit board.
Brush vigorously
to
"thoroughly
clean the top
and
bottom
of the
board
and
allow the
board to dry completely before applying power
to the
limiter
.
In
extreme cases
it
may be necessary to replace the socket which holds
Q7.
Repeat the moisture test before replacing top
and
bottom
covers
.
5.6
CLEANING THE LIMITER
The front panel of the 1178 may be cleaned
with
a
non-abrasive
cleanser such
as
"Formula 409" or "Fantastic" applied
with
a
soft
clean cloth.
Additional protection
of the
anodized panel can be
afforded through
a
light application of
a
spray wax preparation such
as
"Pledge."
Never spray the panel directly,
as
the cleanser
or
wax may adversely affect contr
ols or
meter
,
and can
contaminate
circuit boards
if it
penetrates the chassis.
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Table of Contents
Troubleshooting
