Zenith 28T925 User manual

PHOTO FACT* Folder
ZENITH MODELS 28T925,
28T96O, 28T961, 28T962, 28T963
VERT. CENT.
CHANNEL
SELECTOR
FINE
TUNING
VERT.HOLD
FOCUS
HORIZ. CENT.
DIAL LIGHT 5W,
HORiZ. DRIVE
CONTRAST
CONTROL
VOL.CONT.
ON-OFF SW,
BRIGHTNESS
HORIZ. PHASE
HORIZ. HOLD
VERT.LIN,
HEIGHT
WIDTH
ZENITHMODEL 28T960
.TRADE NAMEZenith,Models 28T925, 28T960, 28T961, 28T962, 28T963. Chassis 28F20, 28F20Z, 28F21,
28F22.
MANUFACTURER ZenithRadio Corp., 6001 Dickens Ave., Chicago, Illinois
TYPE SET Television Receiver
TUBESTwenty-eight
POWER SUPPLY 117 Volts, 60 Cycle AC
TUNINGRANGEChannels 2 through 13 RATING 3.11 Amps @ 117 Volts
AGO Adjustment
AlignmentInstructions
BlockDiagram
Horizontal Frequency Adjustment
HorizontalPhaseAdjustment
Parts List and Description
Photographs
Capacitor Identification
Chassis-Top View
INDEX
20 Photographs(continued)
6,7
10
20
20
14,15,16,17
5,8
PowerSupplyChassis
RF Tuner
Resistor Identification
Trans., Inductor and Alignment
Identification
Schematic
Tube PlacementChart
Voltage and ResistanceMeasurements
19
10
11,18
4,9
2
12
13
HOWARD W. SAMS & CO.,INC. . Indianapolis 7, Indiana
"The listing ofany available replacement part herein does not constitute inany
case a recommendation, warranty or guaranty by Howard W. Sams & Co., Inc.,
as tothe quality and suitability of such replacement part. The numbers of these
parts have been compiled from information furnished to Howard W. Sams & Co.,
Inc., bythe manufacturers ofthe particular type of replacement part listed."
"Reproduction or use,withoutexpresspermission, of editorial or pictorial con-
tent, inany manner, is prohibited. No patent liability is assumed with respect to
the useofthe information containedherein. Copyright 1949 by Howard W.
Sams & Co., Inc., Indianapolis 7, Indiana, U. S.of America. Copyright under In-
ternational Copyright Union. All rightsreservedunderInter-American Copyright
Union (1910) by Howard W. Sams 8, Co.,Inc." Printed inU.S.of America
DATE 6/49 4912-15 SET#64 FOLDER 15
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A PHOTOFACT STANDARD NOTATION SCHEMATIC
© Howard W. Soms & Co., Inc. 1949
PAGE 2

THE COOPERATION OFTHE MANUFACTURER OF THIS
RECEIVER MAKES IT POSSIBLE TO BRING YOU THIS SERVICE

ANTENNA ADJ.
CHASSIS TOP VIEW
C9618Z 'Z96L9Z '196JL8S 'O9618S
S13QOW H1IN3Z

CHASSIS BOTTOM VIEW-TRANS., INDUC
PAGE 4

JCTOR AND ALIGNMENT IDENTIFICATION
PAGE 9

IVO-AOA wonoa SISSVHO
9 39Vd

CAPACITOR IDENTIFICATION
PAGE 5

ALIGNMENTINSTRUCTIONS
VIDEO IF ALIGNMENT
Connect a -1.5 volt bias battery to AGO line.Remove theAGO tube (V8) and connect the negative side ofthe bias
battery to testjack "0"andthe .positive side to chassis.
Connect the synchronizedsweep voltage from the signalgenerator tothe oscilloscope horizontalamplifierInput
for horizontaldeflection.
Remove the oscillatortube (V3) during the video IF alignment.
To disable the high voltageremove the horizontaloscillatortube (V22) from its socket.
DUMMY
ANTENNA
500MMF
500MMF
500MMF
500MMF
Direct
Direct
SWEEP
GENERATOR
COUPLING
High side to pin 1
(Grid) of 6AH6 (V6)
..ow side to chassis
High side to pin 1
[Grid) of 6AU6 (V5)
jOW side to chassis
-Ilgh side topin1
(Grid) of 6AU6 (V4)
Low side to chassis
Ilgh side toan
ungroundedtube
shield slippedover
the convertertube.
Low side to chassis
SWEEP
GENERATOR
FREQUENCY
24MC
(10MC
Sweep)
MARKER
GENERATOR
FREQUENCY
21 .-6MC
25.9MS
25. SMC
22.2MC
25. IMC
27. SMC
21. SMC
21. SMC
22. SMC
25. IMC
25. SMC
27. SMC
CHANNEL
Any
"
n
CONNECT
SCOPE
Vert. Amp. thru
100KS2 to test
Jack "S" . Low
side to chassis.
ADJUST
Al, A2
A3
A4
AS
AS
A7,A8
A9,A10
REMARKS
Adjust AlandA2to obtainpattern
as perFig1 withpeaksbeing of
equalamplitude andthe 21.6MC
marker properlyplaced onthe pat-
tern.Adjust A3to place 25.9MC
marker atthe high freq. peak.
Check position of 21. SMC marker.
If necessaryrepeatadjustment of
Al, A2andA3.
Reduce sweepgeneratoroutput until
amplitude is approximatelysame as
thatobtained in step 1. Adjust A4
for pattern and placement of 25. SMC
marker asper Fig Z.
Adjust for pattern and placement
of 22.2MC marker asper Fig 3.The
25. IMC shouldfallapproximately
as shown in Fig 3.
Use maximummarker amplitude and
adjusttrap ASso 27. SMC marker
disappears at "notch" asper Fig 3.
Adjusttraps A7and AS for minimum
indication of 21. SMC marker asper
Fig 4.
Adjust A9andA10 alternately for
reasonably flat topped pattern as
per Fig4. Checkmarkers tosee
that theyaopear at proper points
on the pattern. The K. SMC marker
is located at 50% onthe high freq.
slope side ofthe overall video IF
pattern (Fig 4) .
SOUND IF ALIGNMENT
The sound IF transformers used in thisreceiver have specially designed slug's and require a special alignment
tool. (Zenith Part No. 68-7). Bothslugs of eachtransformer are accessiblefrom the hole inthetopofthe trans-
former. The alignmentwrench is partiallyinserted to align thetop winding and fullyinserted to adjust the slug
forthe bottom winding.
DUMMY
ANTENNA
500MMF
500MMF
500MMF
500MHF
SWEEP
GENERATOR
COUPLING
Ugh side topin1
(Grid) of 6AU6 (V13)
.,ow side to chassis.
-ligh side topin1
(Grid) of 6AU6 (Via;
Low s ide to chassis.
•liEh side topin1
(Grid) of 6AUS (Vli;
Low side to chassis.
Ilgh side toan
ungrounded tube
shield placedover
the mixertube
(V3). Low side to
chassis .
SWEEP
GENERATOR
FREQUENCY
24MC
(IMC
Sweep)
"
n
MARKER
GENERATOR
FREQUENCY
21. SMC
"
"
CHANNEL
Any
•
"
CONNECT
SCOPE
Vert, &mp. to
Polnt^N Low
side to chassis.
Vert. Amp. to
Point-op Low
side to chassis .
"
ADJUST
All,
A 12
A13,
A14
A15,
A16
A17
REMARKS
Adjust AllandA12for maximum
amplitude and symmetry asper Fig 5
with 21. SMC marker at center. The
peak to peakdiscriminatorwidth is
approximately 450KC.
Adjust for maximumamplitude and
symmetry asperFig6.
"
3.
7.
10.
FIG. 3
PAGE 6