Example Of Repair - Yamaha EMX512SC Service Manual

3.

Example of Repair

All DC voltage is not output from secondary side.
3-1 Instruction
Follow the instruction below. (See section 3-2 and diagram 3-3 on page 86.)
1 Check the resistor value of R418 and R424 (6.8 Ω, 5 W).
If opened, replace R418 and R424.
2 Check the resistor value between C-E of Q406 and Q407.
If short-circuited or the resistor value lowers by several values (Ω), remove Q406 or Q407. Also replace IC402 because it is
broken.
3 Check the resistor value of R419 and R421 is 33 Ω.
If opened or the resistor value increases, replace R419 and R421.
If short-circuited or the resistor value is extremely small, replace D404 and D405. After replacing D404 and D405, check the
resistor value again.
4 Check the resistor value of R440 is 220 Ω.
If opened or the resistor value increases, replace R440. Also replace Q414 because it may be broken.
5 Check the resistor value of R429, R430, R453 and R454.
If opened or the resistor value increases, replace R429, R430, R453 or R454.
6 Check the resistor value of F401.
If opened, replace F401.
7 Check the resistor value between following pins of IC402 with the analog multi tester. When checking, put negative (-) side of the
analog multi tester to pin 4.
Pin
1 Pin 4-5 (GND-LVG)
2 Pin 4-3 (GND-Vcc)
3 Pin 4-2 (GND-HIN)
4 Pin 4-1 (GND-LIN)
* The resistor value is the standard value. Replace IC402 if the resistor value is extremely different from the standard.
If the resistor value is out of the range, counter with the problem in the way specified in the "Remedy" section of the table above
and check the resistor value again.
8 Check the AC input voltage is appropriate for the destination.
9 After checking items 1 to 8 , put the AC power and check the waveform between pin 4 (GND) and pin 5 (LVG) of IC402 with
oscilloscope. Check the measured waveform is the square wave (0-15 V) around 70 kHz.
If the measured waveform is abnormal, check the output of IC403 (3-pin regulator) is +15 V.
If the output is less than +15 V, replace IC402 and check the waveform again. If IC402 is already replaced, replace IC401.
For the normal waveform, see the figure on page 72.
0 Check the "2. Electrical Performance" is satisfied. If satisfied, repair is finished.
*Resistor Value Remedy
approx. 10 kΩ Replace IC402.
approx. 5.5 kΩ Replace IC403. If the problem is not resolved, replace IC401.
approx. 500 MΩ Replace IC402. If the problem is not resolved, replace IC401.
approx. 500 MΩ Replace IC402. If the problem is not resolved, replace IC401.
EMX512SC/EMX312SC
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