Tandy 2000 Service Manual page 182

Tandy@
Model
2000 Service
l,tanual
Start-Up
First note the position of the input vortage select
wire.
This wire
can be found
at the
end
of ttre pig
opposite
the
input/output connectors.
Make
sure that the ioip.r wire is
in the
proper
voltage location.
Load
the
power supply
with
minimum
load as specified in
Table 7-7. Bring
power up slowly with the variable
transformer
while monitoring the
+5 volt output with
the
scope and
DVI{
and
the input with a
DVM
and
wattmeter. rf
the
wattmeter
shows
significant
power
with
row
AC power
being
appried, shut
down
and
refer to section folrowing
on
No
ourPUT- the.suppry should
start with
approximately
80-120
vac applied
and should
regurate
wrren-
9s vac
is
applied. If the output
has reached +5 volts,
do
a
performance test as
shown
in
PERFORMANCE
TEsr which
follows.
NO
OUTPUT
Check
Fuse. If the fuse is
blown, replace
it but
do
not
apply
power
until the
cause
of failure is
found.
Preliminary
check on
Major primary components.
check
thermistor (Rl), diode bridge (DBl),
power
transistor
(Q2),
and catch
diode (D3), turn-off Lransistor (eI),
emitter resistor (R10),
and
diode
(D1)
for
shorted
junctions. rf
any
component
is
found shorted,
replace
ir.
Preliminary
check on lvlajor secondary
components.
using
an
ohmmeter
f!9* output
common
to
each
output (with
output loads disconnected),
check
for
shorled
rectifiers or capacitors. If +I2 volt output is
shorted, arso
check crowbar scR
(scRl)
and zener (zL).
Check
For
B+. Set
up power supply
and
attach
X10
scope
probe ground
to
end
of Rlr crosest to input
capacitors.
Slowly
turn
up power and check
for
B* on
the
t+t
terminal of the
diode
bridge (DBl).
With
the input
at
95
Vac, this point
should be I20-L40
Vdc. If this is
not
measured, check
the fuse, thermister (Rl), DBl,
R2,
D3, and
input capacitors
C6
and
CZ.
4.
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173
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