Chapter 7. GENERAL SUPPORT MAINTENANCE

11-6625-255-14/TO

33A1-13-170-1

CHAPTER 7

GENERAL SUPPORT MAINTENANCE

Section I. GENERAL

7-1. Voltage and Resistance Measurements

circuit tests as follows:

It shall be assumed that general support mainte-

CAUTION

nance personnel are capable of making most volt-

Do not remove or replace parts before

a g e and resistance measurements without de-

r e a d i n g the instructions given in Sec-

t a i l e d step-by-step instructions. Observance of

tion III, Maintenance of Spectrum

t h e following techniques will generally prove

Analyzer.

helpful.

( 1 ) Remove top and bottom dust covers.

a. W h e n m e a s u r i n g v o l t a g e s , u s e t a p e o r

(2) Remove all tubes and dial lamps.

sleeving to insulate the entire test prod except for

c. Measurements. Make the resistance meas-

the extreme tip.

urements indicated in table 7-1. If abnormal re-

b. U s e t h e s a m e o r e q u i v a l e n t m u l t i m e t e r

s u l t s are obtained, perform the isolating proce-

specified on the voltage and resistance diagram

dures described. When the faulty part is found,

(fig. 7-8).

repair the trouble before applying power to the

c. When servicing the Wien bridge assembly,

equipment.

be careful not to disturb the placement of parts or

d . Additional Voltage Checks. W h e n m a k i n g

to bend the tuning capacitor plates; a short circuit

repairs in the spectrum analyzer always check, in

or change of alignment may occur.

a d d i t i o n to the resistance measurements, the

d. Make resistance measurements only as di-

power supply output voltages before putting the

rected on the voltage and resistance diagram (fig.

equipment back into service. Refer to table 7-2 for

7-8) .

procedures.

e . The color code diagram for resistors and

NOTE

c a p a c i t o r s (fig. FO-1) provides pertinent resist-

W h e n the spectrum analyzer is being

a n c e , voltage rating, and tolerance information.

operated from a 115V ac power source,

7-2. Checking Filament and B+ Circuits

t h e regulated +225 volts dc obtained at

for Shorts

pin 8 of V8 must be between 220 and 230

a. When to Check. When either of the following

volts dc for a variation in line voltage of

conditions is in evidence, check for short circuits

1 0 5 to 125 volts ac. If the spectrum

and clear the trouble before applying power.

analyzer is being operated from a 230V

( 1 ) When abnormal symptoms are present

a c power source, t h e regulated +225

whose origins are unknown.

volts dc obtained at pin 8 of V8 must be

( 2 ) When abnormal symptoms discovered

between 220 and 230 volts dc for a line

d u r i n g operational tests indicate possible power

variation of 204 to 256 volts ac.

supply trouble.

b. Conditions for Tests. Prepare for the short

Table 7-1. Checking Filament and B+ Circuits for Shorts

Isolating procedure

Normal Indication

Point of measurement

A lower reading maybe due to a short in

170K

Pin 3 of V11 to ground (figs. 7-2 and

capacitor C 17 or C lg.

7-6) .

An infinite reading may be due to open

resistor R49, R50, R51, or R56, or

open choke L1.

150K

If resistance is zero or infinite, check

Pin 3 of V8 to ground (figs. 7-2 and 7-

C17, C37, R84, RS5, and L1.

6).

If resistance is not within ±10 percent,

Junction of R68 and C18D (A model),

180K

check C18D (C38C) and R67.

R68, and C38C (B, C, and D models)

(fig. 7-5).

theses indicates that the latter is used in

NOTE

a l l models other than the TS-723A/U.

As in chapter 6, a reference symbol

f o l l o w e d by another symbol in paren-

Change

7-1