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NOS-95. Why does zener diode ZD3 keep burning out?

Posted by Marc on

  • Marc Apr 17, 2020

    Sorry, when I say polarity change I mean adjusting the knob on the back of the sub

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Tom Chichester

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You may have to replace the zener with an equivalent having a heftier current rating.

Posted on Dec 12, 2020

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vogesclive

Clive

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SOURCE: Boston Acoustic 5.1 surround, auto-on subwoofer. ZD3 diode fried brown, system works without diode, do I need to put in a new diode? If so, which direction is +.

Re polarity - the diode should have a band nearer one end.
This band is the cathode.
Usually labelled k in schematics.
The un-banded end is the anode.
Usually labelled a in schematics.
On a standard rectifier diode:
The positive + supply enters the diode at the anode and exits at the anode.
However, the component's ID is ZD3, which tells me that this is a Zener diode.
A zener diode is connected opposite polarity to a standard rectifier diode, as it only conducts when reverse voltage from k to a exceeds a pre-determined level.
This is probably part of a voltage regulation or voltage clamping circuit.
ie: when voltage on 'k' line which is positive goes above 'X' volts the zener will conduct, shunting voltage to ground or another part of circuit.
So on ZD3, band is +.
A new diode is advisable, as it serves as over-voltage protection.
The caveat is what voltage rating of zener diode you will need.
A schematic of the sub will be needed to know this....

Posted on Nov 27, 2017

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