The machine power points A, B two boards are placed on the side of left and right speakers, through the socket is connected, loading and unloading is very convenient, and briefly the circuit diagram is shown below. 4Yfservice manual download site
After a preliminary examination, found the fuse F801 fuse and the lining has been blackened. Analysis is caused serious short circuit. Pull out the plug after S86 and the demagnetizing coil plug, measuring D86 {1} foot forward and reverse the ground resistance are above 15 k Ω, show no short circuit phenomenon. Insurance tube fitted with A 3.15 A colour TV, in the case of pull S86 plug boot, measuring D86 {1} side no output voltage, the detection current limiting resistor R803 Ω / 10 w (2.2). After change new boot, measuring D86 {1} feet have 300 v output voltage, A plate has been trouble-free, check B board should focus on. (if D86 {1} feet higher than 350 v, output voltage, input voltage switching circuit fault exists. When emergency repair, can remove the Q804, then according to the usual bridge rectifier circuit works.) 4Yfservice manual download site
 4Yfservice manual download site
 4Yfservice manual download site
Measuring plug S86 {1} feet, approximate short circuit to ground resistance and check the switch tube Q801 (D1391) three pole have been breakdown. The machine switch power oscillation principle is briefly as follows: 300 v voltage by switching transformer T801 to switch tube Q801c power supply, at the same time by starting resistance R813, R817, R819 offer Q801b extremely bias voltage, at the same time, under the action of positive feedback element C817, R820 makes switch power supply. In order to reduce the interference, line flyback pulse through R823, D815 to Q801 b, the oscillation frequency of switch power supply and line frequency synchronization. 4Yfservice manual download site
Check the starting resistance and C817, R820, all without exception. At this time also need to examine Q801 e R835 limit flow resistance, because R835 work in large current status, when damage to the machine for some factors make R835 open Q801 e extremely disconnected at this time, the b and c will be under very high peak pulse voltage and damage. Check the result is no exception, so decided to change my new tube of commissioning. No D1391 sold on the market, with parameters similar D1402 substitution, is safe, pull the plug after S84 connected to 60 w bulb as a dummy load, electricity measurement S84 {1} feet can output stable 113 v, S85 each voltage output is normal. Power will each plug restorable after commissioning, everything is back to normal.

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