Need help selecting a zener on my Onkyo M504, Scematic attached - diyAudio
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Old 17th January 2013, 08:49 AM   #1
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Default Need help selecting a zener on my Onkyo M504, Scematic attached

Found a dead zener in my M504. The type is a 1s2076 which is a 30 volt zener. The zener I recieved from my vender is a 1s2076A which is a 60 volt zener. Looking on the attached schematic will this affect the circuit. It seems to be a -1.1 volt circuit. Not sure. The Diode number on the schematic is D431 located in the driver stage of the amp. Thanks in advance!
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File Type: pdf hfe_onkyo_m-504_service.pdf (689.3 KB, 16 views)

Last edited by jasoneyes01; 17th January 2013 at 08:52 AM.
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Old 17th January 2013, 08:58 AM   #2
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Can't find it - maybe you could just post the sheet with the zener and encircle in red or something.

But in general, there WILL be consequences if you replace a 30V zener with a 60V one, unlikely it will work correctly.

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Old 17th January 2013, 09:17 AM   #3
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Jason, have another look. I see D433 & D434 as 1S2076TD and D431 & D432 as 1SS133.
Some confusion there.
D431 is also shown with a normal diode symbol, whereas for example D451 is the zener symbol.
D431 is located on page 8, connected between the collector of Q431 and the base of Q435. Almost dead center of the page.
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Last edited by sofaspud; 17th January 2013 at 09:21 AM.
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Old 17th January 2013, 09:18 AM   #4
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It's located in quadrant C3 on page 7. This PDF is locked so I cannot annotate it.
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Old 17th January 2013, 09:20 AM   #5
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My bad, it's D433
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Old 17th January 2013, 09:53 AM   #6
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Looking at the schematic D433 doesn't appear as a Zener... The data sheet states Silicon Epitaxial Planar Diode...
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Old 17th January 2013, 09:57 AM   #7
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1S2076TD is not a Zener Diode but an ordinary diode with a reverse voltage of 30v. Fitting a 1S2076A in its place which has a reverse voltage of 60 volts should not affect the operation of the circuit which is part of the overload/short circuit protection. For symmetrical operation D431 & D433 should be the same type. What worries me is what caused this diode to fail in the first place and how did you find it?
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Old 17th January 2013, 10:08 AM   #8
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What caused the diode to breakdown was related to a cracked circuit board. The circuit board crack due to 2 missing screws in the heat sink. Dumb me wasn't thinking when I received it, not starting it up with a Variac and a light bulb. it cooked 6 transistors, 3 resistors and 1 diode all in the driver stage. did'nt make it to the output devices. It was just the left channel. Something to note in this M504 is that all the caps checked good for ESR besides the one's labeles "Sanyo". Several had high ESR. I can recall, Sanyo wasn't real quality back in the early 80's.
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