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Old March 15th, 2012, 8:29 AM
coolguy coolguy is offline
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Exclamation VTF2-MK3 Blown Fuse- cause and probable fix.

Two days back while watching a movie heard a pop noise from the subwoofer. Did not realize immediately that the subwoofer was blown.

Checked the power cord seemed ok, no LED light on amp. Checked the fuse, it was blown. PCB looked normal no blackened components or blown up parts.

Ordered a new fuse. Decided to check the amp for any shorts. On the power supply board there are 2 MOSFET transistors (IRF740) on one heatsink . One of them was shorted. Looks like it gave up the ghost after working so hard for the last couple of movies. The double sided board is a pain to work with also the position of the transistors make it difficult to remove them without damaging some of the track. Had to cut out the legs of the transistor to remove them, ended up damaging some of the track in the process.

Have placed an order for 2 transistors (IRF 740PBF - had same specs as the IRF740) from digikey $1.63 each + shipping. Hopefully this will fix my beloved HSU subwoofer.

This post is being done for those electronically inclined and have some soldering / trouble shooting experience. Could be cheaper to fix rather than ship the amp and get it fixed.

Disclaimer: Do not attempt removing parts from the amp unless you know what you are doing. It is very easy to damage the circuit board while trying to desolder the components. (I used solder wick, that helped some but not much). Looks like at the HSU labs they use the professional vacuum suck removal method.

Last edited by coolguy : March 15th, 2012 at 8:41 AM.
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Old March 19th, 2012, 5:56 PM
coolguy coolguy is offline
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Replacing the MOSFETs did not fix the issue. I measured 161 volts at the capacitors. There is a small hum noise near the first transformer. No output voltage at the terminals of the power supply board.

Due to the lack of a circuit diagram I am unable to fix this board. How do I go about getting this fixed?

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Old March 21st, 2012, 9:55 AM
Ryan_Hsu Ryan_Hsu is offline
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Hi Coolguy,

Feel free to call us to receive an RMA number to have your amplifier looked out by out technicians. Even though you are technically inclined, we would have to take a look at the amplifier to diagnose what is wrong.

If you have any additional questions, please feel free to contact us.

The Hsu Research Team
985 N. Shepard Street
Anaheim, CA 92806
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