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Help. Accidentally dropped needle on record. Blown amp result

Homer4beer

Homer4beer

Well-Known Member
Hi guys,

I was playing a record yesterday through my Onkyo A-9755 amp and at the end of the side my turntable didn't auto return. When I was manually returning the needle I got bumped and the needle dropped back onto the turntable bouncing once before stopping. The turntable was not turning at the time.

The volume was at about the 10:30 position so not even half way however it made a lot of noise when the needle fell and tripped the amp.

When I turned the amp back on it made a terrible squealing noise then blew the main fuse in the amp.

I replaced the fuse, turned the amp back on and had the fuse blow again immediately. Again I replaced the fuse and used my dim bulb tester before switching the amp on.

Now when I turn it on there is a pause for approx 2 secs then the amp clicks on, the bulb lights up and then clicks off again immediately, then cycles over and over again like this.

What on earth have I done to the amp for this to happen and how can I fix this?

It's a class D amp, not solid state so I really don't know where to start and what may have been damaged.

Help very much appreciated.

Thanks guys :)
 
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Protection mode i would gather.... Possibly blew some output transistors? Have to open her up and check.... Check the fuses first, but if they are good then move to transistors. Hopefully one side is still good, check by removing one fuse for one side of amp board and see if unit turns on. If not try the same thing for other channel. If you find one channel is still working, you will have a reference to go with for component testing...
 
Just looked at some shots of this amp, sure looks like a nice unit, but it could possibly be hard to work with. Hopefully you can get to the bottom of the problem...
 
Well, consider the amount of amplifier power required to reproduce that needle drop given the incredibly high gain of the phono preamp. Have you verified that one or both of the speakers could have been damaged as a result?
 
Thanks for the replies guys.

It really wasn't that loud when the needle dropped which is why I'm surprised it damaged the amp. I'll fix the amp then check the speakers as I really want the amp up and running asap.

I'm not sure it's in protection mode as protection mode shouldn't allow the main power fuse to blow?

Being a digital class D amp I'm not sure where to start :(
 
Damn sorry to hear this. I don't have steady surgeon hands and that's why I went with a semi auto. Perhaps it's a lack of practice but the first time I set the needle down and aligning it was not pretty. I just bought a new one.
Hope you get yours fixed.
 
I feel lucky cause I've done that so many times and nothing has happened....

Just from letting the cart bounce off vinyl while at stand still ???
 
SVI2004A said:
Don't bother with class d... cut your losses and get a much better amp... Onkyo made plenty of good models
Click to expand...

I actually really like the amp. It's had excellent reviews and sounds great for its price so I do want to fix it.

I also don't want to spend money on a new amp at the moment.
 
Looks like it's little chip has lots of power supply.

I'd be wondering about the needle drop damaging a speaker which has presented a damaging load to the amp.

72611.jpg
 
Homer4beer said:
I'm not sure it's in protection mode as protection mode shouldn't allow the main power fuse to blow.
Click to expand...

If its blowing the main fuse, a shorted transistor is usually one of about 3 prime suspects. Hey, I feel for you man. A friend of mine once blew a channel on one of my amps simply by turning off a musical instrument keyboard that I had connected to it. My volume was also at about the 9 or 10 o'clock position and it produced a pop or thump that took out an output transistor for one channel.

Back to tubes. :D
 
The specs say all discrete output stage circuitry.

Apparently a digital amp doesn't need large heat sinks?

I would be looking for a blown driver or output transistor. Possibly on the heat sink by the main caps.

Rob
 
Is it under warranty? Seriously, a bouncing cartridge across a record is a pretty common occurrence and although it gives you a scare, it shouldn't destroy an amplifier that is competently designed.

That said, the rated phono overload on that amp is a paltry 70mV, meaning a large overload early on could have pushed the amp into oscillation and destruction.

If the amp is indeed dead, I would be seeing what Onkyo will do about it.
 
Unfortunately it's not under warranty. The Onkyo repair agent wants $120 an hour plus parts to fix it.

Struth!
 
$120 an hour... plus the parts.

You can - for now - buy with this money a "spare" integrated and decide later what to do with the nice Onkyo...
 
Yep I have a main home theatre amp which I use for TV viewing however the phono sounds terrible on it as well as stereo listening :(

I'd love to try and fix my Onkyo. I have a very good oscilloscope so I just need assistance from the experts in this forum on how to go about problem solving and repairing.

Thanks guys :)
 
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