(1) CR8 shorted.

(2)

Q8

shorted.

(5) R40, R43 open. e

.

If the 32vdc output cannot be obtained in step d, reconnect diode CR8 and turn t h e front-panel VOLTAGE controls t o mid-position. f .

Using the oscilloscope, check t h e following:

(1) Waveform across t e s t points 3 1

(positive 1ead)and 33 (waveform on figure 4-2). If peak negative voltage is less than 15 volts,

97,

R53, CR48, C25,

C26, or transformer T3 may be defective.

(2) Ripple waveform across t e s t points 18 (positive lead) and 48 (wave- form shown on figure 4-2)

.

If waveform is correct (except for amplitude), proceed t o s t e p (3). If wavefom is incorrect, proceed a s follows:

(a) If the ripple waveform is half-wave (60 cps) instead of full-wave

(120 cps), either SCR (CR17 or CR18) may be open or t h e applicable gate circuit for t h e SCR may be defective. To check the g a t e circuit, disconnect R54 or R55 ( a s applicable) and make a n ohmmeter check from the open end of the resistor t o t e s t point ACC or 45 ( a s applicable). If the resistance is greater than 55 ohms, t h e gate circuit is defective

.

(b) If the ripple waveform indicates that neither SCR h a s fired, CR17 or CR18 may be shorted.

(c) If there or

T 1 may be defective. is no ripple waveform, both CR17 and CR18 may be open g. Using t h e differential voltmeter, proceed as instructed i n table 5-5.

5-48. COMMON TROUBLES. Table 5-6 gives t h e symptoms, checks, and probable c a u s e s for common troubles. The checks should be made using a 115-volt, 60-cps, single-phase power input and the t e s t equipment listed in table 5-1.

5 -49. REPAIR AND REPLACEMENT

5-50. Before servicing etched circuit boards, refer to figure 5-7. After replacing a semiconductor device, refer t o table 5-7 for checks and adjustments that may be necessary. If a check indicates a trouble, refer t o paragraph 5-39. If a n adjust- ment is necessary, refer t o paragraph 5-51.

S E R V I C I N G ETCHED CIRCUIT B O A R D S

Excessive heat o r pressure can lift the copper s t r i p from the board. Avoid damage by using a low power soldering iron (50 watts maximum) and following these instructions. Copper that lifts off the board should be cemented in place with a quick drying acetate base cement having good electrical insulating properties.

A break in the copper should be repaired by soldering a short length of tinned copper wire a c r o s s the break.

Use only high quality rosin c o r e solder when repairing etched circuit boards. NEVER USE PASTE FLUX.

After soldering, clean off any excess flux and coat the repaired a r e a with a high quality electrical varnish o r lacquer.

When replacing components with multiple mounting pins such a s tube sockets, electrolytic capacitors, and potentiometers, it will be necessary to lift each pin slightly, working around the components several times until i t is free.

WARNING: If the specific instructions outlined in the steps below regarding etched circuit boards without eyelets a r e not followed, extensive damage to the etched circuit board will result.

1. Apply heat sparingly to lead of component to be replaced. If lead of component passes through an eyelet in the circuit board, apply heat on com- ponent side of board. If lead of component does

- ductor side of board.

2. Reheat solder in vacant eyelet and quickly in- s e r t a small awl to clean inside ofhole. If hole does not have an eyelet, insert awl o r a

#57 drill from conductor side of board.

CONDUCTOR

4.

Hold part against board (avoid overheating) and solder leads. Apply heat to component leads on

3. Bend clean tinned leads on new part and care- fully insert through eyelets o r holes in board.

pJJ-.,

-c-=-=aw

In the event that either the circuit board h a s been damaged or the conventional method is impractical, use method shown below. This is especially applicable f o r circuit boards without eyelets.

1. Clip lead a s shown below.

2.

Bend protruding leads upward. Bend lead of new component around protruding lead. Apply solder using a pair of long nose pliers a s a heat sink.

C L I P

HERE

APPLY

SOLDER

This procedure i s used in the field only a s an alternate means of repair. It is not used within the factory.

Figure

5-

7 .

Servicing Etched Circuit Boards

5-13