Model 122A/AR Section VI11
Paragraphs 8- 1 to 8-8
SECTION Vlll
SCHEMATIC DIAGRAMS
8-1. SCHEMATIC DIAGRAMS. same tube section, such as t for triode and p for pen-
tode. A socket terminal withan asterisk may be used
8-2. GENERAL NOTES. as a tie point and may have a voltage and resistance
8-3. The schematic diagrams, Figures 8-3 through shown.
8-9, are in this section of the manual. They are drawn
to show the electronic function of the circuitry and the b. Voltage values shown are for guidance; values
circuits shown on one schematic may include all or part may vary from these shown due'to tube aging or nor-
mal differences between instruments. Resistance
of several different functional areas. Generally, the values may vary considerably from those shown when
schematics cover the Vertical Amplifiers and their the circuit contains potentiometers, crystal diodes,
input switching, the Horizontal Amplifier. the Sweep or electrolytic capacitors.
Generator and its time switching, the High Voltage
Power Supply, and the Low Voltage and Filament c. Voltage measured at the terminal is shown above
Power Supply. Figures 8-1 and 8-2 are included to the line, resistance below the line. Measurements
indicate the normal voltage and resistance values to are made with a vtvm from terminal tochassis ground
befound attube socket pins, as an aid totroubleshoot- unless otherwise noted.
ing. Adjustable components are identified and located
in Figures 5- 1, 5-2, and 8-2. Waveforms are indicated d. A solid line between socket terminals indicates
on the schematics near the point where they may be aconnection external to the tube between the terminals;
measured and observed on a separate oscilloscope, if a dotted line between terminals indicates a connection
inside the tube. Voltage and resistance are given at
required. only one of the two joined terminals.
a. Heavy solid lines in the schematic show main
signal paths. 8-5. REMOVING THE CHASSIS.
b. Heavy dashedlines show control, secondary sig- 8-6. Disconnect the power cable and remove two large
nal, or feedback paths. screws on the rear of the cabinet (Model 122A) and
slide the chassis forward out of the cabinet. Access
c. Heavy boxed callouts indicate f ront panel labeled to the chassis (Model 122AR) may be gained top and/or
controls. bottom by removal of four screws.
d. Light boxedcallouts indicate chassis markings.
e. Arrows on potentiometers indicate clockwise piiii-1
rotation as viewed from the round shaft end.
f. Resistance values in ohms, inductance in micro- If the instrument is operated with the
henries and capacitance inpicofarads, unless otherwise cabinet removed, dangerous voltages
specified. are exposed. Take adequate safety
8-4. VOLTAGE AND RESISTANCE DIAGRAM NOTES. precautions, especially when working
around the cathode- ray tube terminals
a. Each tube socket terminal is numbered and let- and the power supplies.
tered to indicate the tube element and pin number,
as follows: 8-7. TUBE REPLACEMENT.
* = no tube element T = target (plate) 8-8. In many casesaninstrument malfunction can be
H = heater R = reflector repeller corrected by replacing a weak or defective tube. Be-
K =cathode A = anode (plate) fore changing the setting of any internal adjustment,
G = control grid S = spade check the tubes. Adjustments that are made in an
Sc = screen grid Sh = shield attempt to compensate for a defective tube will often
Sp = suppressor grid NC = no external connection complicate the repair problem. It is a good practice
Hm = heater mid-tap to socket to checktubes and instrument performance by substi-
IS = internal shield A = indefinite reading due tution rather than by use of a "tube checker". The
P =plate to circuit (see b) results obtained from the "tube checker" can be mis-
leading. Before removing a tube, mark it so that if
The numerical subscript to tube-element designators the tube is good it can be returned to the same socket.
indicates the section of a multiple-section tube; the Replace only those tubes proved to be weak or defective.
letter subscript to tube-element designators indicates Any tube with corresponding standard EIA (JEDEC)
the functional difference between like elements in the designations can be used for replacement.
1
00081- 1 8- 1 |
ACEC
HEWLETT-PACKARD
