Removal From Cabine T - RCA 54-45 Manual

SE RVICING TV RECEIVERS : One major use of the scope in tv servicing is alignment in conjunc­
tion with a TV /FM Sweep Generator.
oscillator stages, following the general method and theory of alignment described in the sweep generator
instruction manuals . The specific methods of alignment depend on the receiver, and the manufac­
turer's service instruction should always be followed.
Another major use of the ' scope is to check the waveform of the complex tv signal as it passes
through the receiver . The exceptional fidelity of the 'scope is very important in this application,
since you must be able to observe small variations in waveform in order to localize and correct the
cause of poor picture quality. Here again, the set manufacturer provides representative waveforms
to be expected at specific points in a specific model of receiver.
furnished for the entire receiver, with the exc eption of the tuner portion.
Keep in mind that two basic frequencies are involved in checking waveform of signals in tv receivers.
The vertical or field frequency is 60 cps . Any waveform check, except with the horizontal oscillator,
its differentia tor network, and the horizontal amplifier stages, can generally be made using an internal
linear sweep frequency of 30 cycles to show two complete fields of the signal. To examine the hori­
zontal pulse shape, or the operation of the horizontal deflection system, it is generally suitable to use
an internal linear sweep frequency of 7875 cps , again to show two complete lines of the signal.
SEC TION IV. MAINTENANCE
4- 1 GENERAL
Included in this section are instructions for trimmer capacitor C 1 adjustment, trouble-shooting,
and parts replacement.

4 - 2 . REMOVAL FROM CABINE T

To remove the instrument from the cabinet, first disconnect it from the power line and remove
the two No . 8-32 x 3/8 machine screws in the cabinet rear. Then slide the chassis out the front of
the cabinet.
4- 3. TRIMMER CAPACITOR C 1 ADJUSTMENT
Connect a jumper from pin 2 of V5 and the VERT. INPUT terminal.
to INT. , the SWEEP RANGE switch at the 1K- 10K position, and the SWEEP VERNIER at MIN.
set the VERT. A TTENUA TOR at m, and then use the panel controls to obtain a centered, focused
trace entirely on the screen. With the trimmer C 1 adjusted improperly, the trace will appear either
as in Fig. 8a or Fig. 8b. If this is the case, adjust C 1 (see Fig. 2) until the hook disappears and the
trace is a straight line as in Fig. 8c. Be sure to use an insulated alignment tool.
A much preferred method of adjustment, when the equipment is available, is to apply a square
wave of approximately 1kc fundamental frequency to the VERT. INPUT and ground terminals . With
the VERT . ATTENUATOR set to m, adjust trimmer C 1 for the best possible square wave reproduc­
tion. Internal sweep is employed and the panel controls set for several stationary square waves on
the screen before adjusting the trimmer for proper frequency compensation.
First, the IF stages are aligned, and then the RF and local
The voltages in this instrument are dangerous . Take
caution to avoid personal contact with these voltages
when the instrument is being operated outside of its
cabinet. Remember that capacitors may remain
charged to dangerously high voltages for a consider­
able time after power has been removed.
WARNING
30
These waveform pictures are
Set the SYNC SELEC TOR
Now