Kenwood A83 dangerous amp?? - diyAudio
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Old 5th November 2003, 07:19 PM   #1
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Join Date: Jun 2001
Location: Flanders, Belgium
Arrow Kenwood A83 dangerous amp??

Hi,

I've just got an amplifier to repair...
The amp was dead, so I decided to look inside....
After some measurements I realised there was no DC power at the collectors of the output transistors, so I looked at the PSU...
It seems that the primary of the transformer is broken, however the primary is almost connected directly to the mains, without a fuse!! The only thing between is a "breaking" relais driven by a small circuit with a different (small) PSU. At the secondary windings there aren't any fuses too!!! The only fuses in this amp are there to connect the mains to other (external) devices.

Maybe I'm wrong, but isn't this a VERY unsafe way to work?? what happens if the rectifierdiodes are short circuited (primary of the transformer will burn??)
Does anybody know where to find some schematics of this amp??


best regards,

HB.
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Old 5th November 2003, 07:38 PM   #2
MarkMcK is offline MarkMcK  United States
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Join Date: Aug 2003
Location: Ohio
Hi HB,

This is a simple one. To prevent owners putting in oversized fuses, most commerical amplifier transformers use a thermal fuse wound into the transformer.

Most likely this has opened. The manufactuerer would want you to replace the transformer to repair the unit (assuming there is no downstream problem to cause this thermal fuse to open). Usually these thermal fuses were not drawn into the schematics.

On some transformers you can get at the thermal fuse. If you can, then the transformer can be repaired.

Good luck,

Mark
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