I worked on a Rockville amp yesterday and found that both of the output inductors were cooked. I haven’t found any other damaged components in the amp. It looks like a very new amp, less than a year old.
I know that vibration damage is a major factor for these inductors to fail, but I’m not sure that vibration caused this failure. What else could cause the output inductors to cook.
David
I know that vibration damage is a major factor for these inductors to fail, but I’m not sure that vibration caused this failure. What else could cause the output inductors to cook.
David
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It looks like it shorted where the terminal windings met the rest of the windings so I'd guess that vibration caused the insulation to wear through.
If no semiconductors are damaged, and the inductors are burned, this has only one cause: heavy looses in them. Then:
1.- The core was not properly chosen for the power/frequency range;
2.- The voltage across the winding or the current flowing (or both) in it was too high;
3.- Too small air flow around the inductor's core.
So the only remedy is to investigate what caused the failure and make or order new inductors properly choosen.
If you choose to rewind them, DO NOT REUSE THE CORE. Once the core increases its temperature above the Curie temp, the core becomes unusable.
For example, if the amp is designed for 8R loads, using it in 2R loads caused too high (four times) currents, causing overtemperature in the winding.
1.- The core was not properly chosen for the power/frequency range;
2.- The voltage across the winding or the current flowing (or both) in it was too high;
3.- Too small air flow around the inductor's core.
So the only remedy is to investigate what caused the failure and make or order new inductors properly choosen.
If you choose to rewind them, DO NOT REUSE THE CORE. Once the core increases its temperature above the Curie temp, the core becomes unusable.
For example, if the amp is designed for 8R loads, using it in 2R loads caused too high (four times) currents, causing overtemperature in the winding.
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They likely failed from shorted windings due to vibration. It's extremely common in amps that were mounted on the speaker enclosure.
The cores rarely heat but it's possible. When they get hot enough to affect the cores, they will typically cause darkening of the board.
The amp was likely designed to drive 1 ohm loads.
The cores rarely heat but it's possible. When they get hot enough to affect the cores, they will typically cause darkening of the board.
The amp was likely designed to drive 1 ohm loads.
Barber do you by chance have the inductance value or number or turns the inductors is wound and what gauge? I lost my notes when i unwound this and let it sit for a bit.
I didn’t save any notes on them except this.... it was a 29uh inductor and you are better off buying a whole new inductor. Preferably one with a better matched core. I rewound the ones I had and returned the amp to it’s owner. They didn’t last two weeks. I refunded him his money and cut my loses.
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