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2.3.3.3.2. Preparations
- Con nect the TV set to the m a i ns via a separating transformer
- Con nect the chassis of the TV set to a proper earth
- Setti n gs of h.f. generator PM 5324
•
Depress range button 30 . 80 M Hz
•
Depress button AM 1 kHz
•
Con nect the h.f. generator to the measuring point i nd icated i n the serv ice documentation.
The scree n i ng of the cable to the chassis should be as short as possib l e
•
Set control H F A M P L I TU D E to maximum
- Connect the ind icator accord i n g to the data g iven i n the documentation of the TV set
- Setti ngs of the TV set
•
Set the channel selector to a free channel or to a position between two channels.
By t h i s the influence of the h.f. band·pass f i l ters i n the channel selector on the term i nation resistor (75
of the h.f. generator is prevented.
•
Set the contrast control to maximum contrast
•
Adjust the AGC voltage to a fixed value. I n most of the cases the connection point a nd the voltage l evel of
the pseudo ·
AGe
2.3.3.3.3. Checking and adjusting
For checki ng tune the i . f . range with control F R E Q U E NCY (e.g. approx. 31 - 42 M H z ).
R ead the measured value in i ntervals and check that the val ues correspond with the recommended band-pass
curve. Bear i n m i nd that the TV set i s not overdr iven; if necessary, reduce the output voltage of the generator
by means o f control HF A M P L I TU D E .
However,
the adjusted output voltage should b e constant d u r i ng the measu rement.
If an i ncorrect adjustment i s expected, only adjust those elements correspond ing to the test c i rcu it. For t h i s
consu lt the service documentation of t h e TV set and t h e relevant d a m p i n g measu res, if necessary.
For more importa nt adjusting faults, it is recommended to carry out a comp lete adju stment in the sequence
given in the documentation and to check the compl ete band-pass curve aga i n .
The sound channel o f a TV set should b e checked a n d adjusted accord ing t o 2.3.3.2.
2.3.4. DYNAMIC MEASURING METHOD
( F ig. 7)
2.3.4. 1 . Principle
For this method, a constpnt frequency-mod u lated r.f. voltage is necessary. Th i s voltage is fed to the test object
which is, i n most of the cases, the i . f . ampl ifier of an a . m . or f . m . receiver.
The frequency-modulated signal and the frequency sweep must cover the entire i.f. range. The demodu lator of
the receiver wi l l then produce a vol tage which is proportional to the ga i n of the separate frequencies. The form
of the a m p l i tude variation corresponds to the band-pass curve of the test object. This voltage is suppl ied to the
i n put of an osc i l l oscope ( Y-input).
A
Voltage, wh ich corresponds to the frequency mod u l ation, i s fed to the X - i nput. This sawtooth voltage can be
derived from the generator at output SW E E P OUT.
The resu lting curve on the screen of the osc i l l oscope represents the band-pass curve of the test object.
Note
Dynamic adjustments of i .f.- and h .f. circuits of TV sets are i mpossible as wobbu l ating at th is frequencies is
i mpossible with t h i s generator.
voltage are stated i n the service docu mentation of the TV set
S1)
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