SAMSUNG SC-7400 Service Manual Troubleshooting

Samsung Electronics 8-1

8. Troubleshooting

TROUBLE SHOOTING FOR SC-7400

1. RADIO

1) FM

a . FM DEAD- * Check FMB+(8V-9V)from collector of Q202 to TUNER pack B+(PIN4).

* Check the voltage of pin 7of IC502(logic high9.6V).

* Check the VT(1-8V according to frequency change) at pin3 of the tuner

pack.

* Check the FM oscillation signal by scope at pin 11 of IC502

* Check B+ IC 101 at pin12

* Check signal at pinl of IC 103.

* Check if mute is being on at base of Q503must be 0.7V.

b. FM WEAK-* Check FMB+ (8V-9V) at collector of Q202

* Check the voltage of tuner B+ at pin3 of tuner pack.

* Readjust FM IF.

* Check AMB+ - must be almost OV, if not so , check band changing circuit.

(Q201,Q202 and out at pin 7,8 of IC502)

c. STEREO DEAD-* Check free run frequency 19KHz at pin 13 of IC 103.

* Check SNC.HCC circuit at pin 7.8of IC103.

* Check the INPUT signal at pin 2 of IC 103.

d. STERO WEAK - * Check composite signal at pin1 of IC 103.

* Check SNC.HCC circuit R124 D104 D105 R151 R123)

* Readjust phase (SV102).

2) AM

a. AM DEAD - * Check the voltage at emitter of Q201(8V-9V).

* Check the voltage at pin8 of IC502 (logichigh 9.6V).

* Check VT at R203 (1.2V-7.8V according to frequency change).

* Check the oscillation signal at pin10 of IC502.

* Check the AM OUT signal at R201.

* Check the voltage at base ofQ504 more than 0.7 V.

* Check the FMB+ voltage – must be almost OV, if not so check band

changing circuit (Q201,Q202, BAND OUT at PIN 7,8 of IC502).

b. AM WEAK - * Check the voltage at emitter of Q201

* Readjust AM TRACKING according to procedure.

3) DEAD BOTH FM AND AM

Samsung Electronics8-2

* Check VDD of IC502 at in pin9(4.5V-5V) regardless ignition status

* Check VDD of IC503 at in pin17,29(4.5V-5V) regardless ignition status

* Check the L.P.F circuit (from pin7,8 of IC502 to Q103,Q104 and each

AM,FM VT terminal).

* Check external circuit of IC502 .

* Check external circuit of IC503.

2. TAPE EQ TROUBLE

1) TAPE EQ DEAD

* Check the voltage at pin1 of IC301(8V-12V)

* Check the wire connection of deck head .

* Check external circuit of IC503

* Check audio output signal at pin 7 and 17 of IC401.

2) TAPE EQ LOW OR HIGH FREQUENCY WEAK

* Check N.A.B. circuit ( R312 R308 C309 R311 R307 C306 R310 R306

C308 R309 R305 C305)

.

* Readjust head azimuth.

3. TROUBLE SHOOTING FOR DIGITAL

1) ALL DEAD

a. Check VDD, CE(pin17,29 (5V)and pin14(5V) of the IC503

b. Check master clock 4.5MHz of the u-com(IC503) by wave or frequency counter.

c. Reset VDD at pin 1.2 of IC501.

2) TYPICAL FUNCITION DEAD

a. Check key matrix continuity between pins of corresponding switch.

b. Check external circuit of IC503.

c. One of the segment of LCD dead-* check the wave forms at common0, common1,

common2 of LCD.

e.* Check the wave form at each segment of LCD.