TROUBLE
ANALYSIS
PROCEDURE
The trouble analysis procedure that follows con-
tains some
of
the typical trouble symptoms encoun-
tered
in
the field and
their
remedies. Other field
problems will
be
covered through service bulletins
(supplementary to this manual) which will
be
issued
to all stations. Other servicing aids included in
this
manual are a component location illustration, figure
12, which locates those transistors and diodes com-
monly requiring servicing in the field, and the sche-
matic diagram
of
the Solid State Amplifier, figure 13.
The schematic diagram contains a Voltage Chart
which lists typical voltages taken at various test
points in a normally-operating amplifier.
NOTE
Performance Verification is necessary fol-
lowing any repair.
SYMPTOM
1. Excessive line consumption
(100
watts or more).
PROCEDURE
a.
Check
for
shorted rectifiers CR114, CR116
(DHC 200R), CR115, CR117 (DHC 200), C15,
C21.
b.
Check for shorted transistors Q107 through
Qll3
(DTMlO, 11, 12, 13, 14), or zener diodes CR109
or
CRll
1 (DIN4732A). Also check for open
lamps
DSlOl,
DS102, control R30, and bias
diode
CRll0.
CAUTION
Because the driver and output stages are direct coupled, many components may fail
as
a direct result
of
an
initial component failure. If a shorted transistor or Zener diode
is
found,
or
an
open lamp, control or bias
diode,
be
sure to check the remaining driver and output components for short or open circuits before re-energiz-
ing the amplifier. After replacement of any
of
these components, increase the Variac voltage slowly while
monitoring the wattmeter
as
described in paragraph C
of
Performance Verification.
2.
No
line consumption
or
zero bias.
3. High d-c voltage at loudspeaker terminals before
time delay circuit
is
deactivated.
4. High d-c voltage at loudspeaker terminals at all
times.
5.
No
D-C
Balance.
6. High hum and noise level.
7. Parasitic Oscillation.
8
Check for open fuse, transistors
QlOl
(DTM6), Q107
through Q113 (DTMlO, 11, 12, 13, 14), zener diode
CR109 or
CRlll
(DIN4732A), or overload indicators
DSl0l
and DS102.
Check transistors Q105 and Q106 (DTM8), and Q104
(DTM9) for leakage. Voltage
on
these transistors
should not vary more than 1 volt.
Check for shorted transistors Q104 (DTM9), Q105 or
Q106 (DTM8).
Check for open transistors Q104 (DTM9), Q105 or
Q106 (DTM8).
Check by substitution transistors
Ql0l,
Q102,
and
Q103 (DTM6). Note that
Ql02
and Q103 are a
matched pair and must
be
replaced
as
a pair.
a.
Remove capacitors
Cl4
(.22
UF)
and
Cl
7 (.0047
UF).
b.
.Check
by substitution transistors Q113 (DTM 13)
and Q114 (DTM14).
(
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