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Old 9th December 2012, 10:05 AM   #21
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Quote:
I measure the voltage at power supply. 22(+/-)VDC correctly supplied to Power-amp but Regulator 7818 is not supplying +18VDC DMM shows below <1 vdc WHY ? I could not understand.
You should separate the power supply from the amp and figure out why you aren't getting regulated output. I can't tell anything from the pic and schematic. Are you sure the switch isn't defective?
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Old 9th December 2012, 10:44 AM   #22
pra3718 is offline pra3718  India
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you are requested to view lm1876.pdf in post #12 (please ignore if seen)

Yes, Today I will try this.
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Old 9th December 2012, 10:50 AM   #23
pra3718 is offline pra3718  India
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At first time, Regulator 7818 is not supplying +18VDC and 2nd time (OFF/ON) shows +18VDC. Very confusing.

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Old 9th December 2012, 11:59 AM   #24
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Try a (reversed) diode across 7818/ 7918 in/out. 1N400x type

Last edited by bobodioulasso; 9th December 2012 at 12:02 PM.
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Old 9th December 2012, 12:11 PM   #25
pra3718 is offline pra3718  India
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Quote:
Try a (reversed) diode across 7818/ 7918 in/out. 1N400x type
If I understood correctly, I was thinking the same. Thank you very much.

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Old 9th December 2012, 01:00 PM   #26
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I also think the problem arose when you added the 5v regulator. Is'nt it?
You do not really need that regulator. A zenner and a resistor would do it.
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Old 9th December 2012, 01:41 PM   #27
pra3718 is offline pra3718  India
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This is another helpful post...# 26

What I will do is.. First I will remove 5v regulator, then try what shows 18V regulator.
If 18V regulator works correctly with several ON/OFF then 5V Zenner will be use.
If 18V regulator does not work correctly then try for (reversed) diode across 7818/ 7918 in/out

After all 5V zenner and resistor is good idea.

Thank you bobodioulasso, you have provided good information for my home-work, Please give me time for trial.
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