INFINITY SSW-10
Manual de Servicio

TROUBLESHOOTING (cont�d)
B. If all voltages are normal: Check for +25 to 30 volts across relay terminals. (See drawing) If voltage is present, replace relay. If little or no voltage is present, check for+15 volts on pin I of IC3 (LF 347N on PC-1). Check for +2.9 to 3 volts on pin 2. Check for +12.7 volts on pin 3. Use main filter caps, (common point), or black power supply wire for ground. If any of the above voltages are abnormal: Check DC voltage across R4 (33K�). (See drawing for location) Less than 50mV should be present. If higher, relay will not energize. DC is coming through the amplifier section. Check and replace semiconductors as necessary. If there is negligible voltage across R4, (normal condition) replace LF 347N IC on PC-1. RELAY CLOSING NORMALLY, BUT NO OUTPUT OR DISTORTION EXISTS Re-read or follow the instructions mentioned on the first page concerning other issues which could result in no output: (bad woofer or mis-wired high level input).

III A.

B. If those items check out, follow the signal path with schematic and DMM (oscilloscope is usually not required), checking for these approximate voltages at the points indicated below. Use main filter caps, (common point), or black power supply wire for ground: TEST CONDITIONS: Signal: l00mV @100 Hz connected to the low level input with a Y-cable (both right & left inputs). Both control pots (level and frequency) Full Clockwise. Turn UUT on. No speaker load should be connected at this time. ICI (LF347N) pin 7: 388 mV ICI (LF347N) pin 1: 392 mV Check C16 (.15µf Capacitor). One or both leads must be unsoldered for proper reading. Replace if defective. IC2 (LF353N) pin 7: 380 mV IC3 (LF347N) pin 14: 138 mV R53 (See drawing): 117mV R48 (See drawing): 2.7 volts Loss of signal at this point means Relay contacts are defective. Replace if necessary. Nominal Output at speaker cable: 2.7 volts Note: When a loss of signal occurs between amplifier stages of different IC's, it's easy to be fooled when one amplifier stage is shorted out, "loading down" the previous section of another IC. NOMINAL POT POSITIONS ON MAIN AMP BOARD � (VR3 - Full CW), (VR4 - Half-way position) Another procedure for confining the problem to one board or the other is as follows: 1) Remove both IC's on smaller filter board (if they are in sockets), if not unsolder 5 conductor ribbon attaching PC-1 to PC-2. 2) Follow "TEST CONDITIONS" above regarding signal injection except lead should be connected to C19 (See drawing for location). 3) Turn UUT on. Output at speaker cable should be .7 - .8 VAC. If output is normal, then problem or loss of signal is on smaller filter board. 19