Tektronix T921 User Manual

Service
Information-T921/T922/T922R
b . Check voltage at junction
of R2147, R2152, and
R2143 .
Does voltage vary from -2 to
+3
V
while turning
LEVEL
control throughout its range? If yes, check
U2156B
output . Does
U2156 output level change while
turning
LEVEL control as
above?
c .
Connect a signal to CH 1 . Check for trigger
pulse at
U2156B output . If
no signal, suspect U2156A
or B, or
related circuits .
SYMPTOM 2 .-Does not trigger in
AUTO .
a . Check for trigger
pulse at pin 6 of U2212B . If
none,
check for HI at U2212B, pin 4,
while varying the LEVEL
control .
If pin 4 does not go HI, check
for defective
U2212B,U2224B,
or CR2227 .
SWEEP : SYMPTOM
1 .-No sweep on crt (see
Sweep &
Horizontal Amplifier
schematic) .
a . Push BEAM FINDER
button . If trace or dot is right
of
center, check at R2243 (end
of resistor toward board
center) for
a 12 V (approximately) ramp .
b . If ramp is not present,
check for approximately 0 .7 V
at 02274 base .
c .
If voltage at 02274 base is high
(approximately 8 .0
volts) check 02274,
02242,02244, or 02246 .
5- 1 0
SYMPTOM 2 .-No trace on crt .
a . Repeat sweep
symptom 1, parts a and b .
b . Check for a HI at U2234C, pin 8 . If not HI,
check
U2234C .
NOTE
When troubleshooting
the sweep or horizontal cir-
cuits, the Vertical Amplifier
may be removed from
the instrument .
Sweep
may lock up while
troubleshooting . If in
doubt, switch instrument
power off and
backon
.
If
there
are no problems,
trace should free run .
HORIZONTAL :
SYMPTOM 1 .-No trace
on screen (see
Sweep and Horizontal
schematic) .
a . Check output (02334-02344
collectors) for ap-
proximately 40 V ramp . If okay, check for possibly
defec-
tive crt leads
.
SYMPTOM 2 .-Trace
is on screen but .short .
a . Check
horizontal output (02334-02344
collectors)
for approximately
40 V ramp .
b .

If no ramp at output, check for
12
V
ramp at junction
of R2243-R2244-R2245 .
c . If
ramp is present, check 02314,
02326, 02332,
02334, or 02344 .
CORRECTIVE MAINTENANCE
Corrective maintenance consists of repair
and parts
replacement
. This section contains general
information,
troubleshooting
information, and component
replace-
ment information .
NOTE
Be sure you
are familiar with soldering techniques
and parts replacement
procedures before replacing
any components .
Soldering Techniques
WARNING
To prevent electrical shock, or
damage to the
instrument,
always disconnect the instrument
from
the power
source before soldering .
The T900 Series uses some
single-sided circuit boards,
i
.e ., wiring is plated on only one
side . The components are
located
on the front of the circuit
boards . The circuit
designations have
been silk-screened onto the
compo-
nent side of the circuit board
next to the components . The
circuit boards are mounted with
the component side out to
allow
access to the components
. If it is necessary to
replace
a component, the leads
may be clipped and the
new part
soldered to the leads of the
previous one .
However, be
careful not to loosen the connection
with the
etched circuit
wiring on the back of the circuit
board .
For
soldering, use ordinary
60/40 solder and a 15-watt
soldering
iron . Excessive heat can
cause the etched circuit
wiring to separate
from the board base material .
Use
caution if using
a higher wattage-rated soldering iron
on
the circuit boards .
REV . B APR 1977

Tektronix T921 Specifications

General

Brand	Tektronix
Model	T921
Category	Test Equipment
Language	English