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Help. Accidentally dropped needle on record. Blown amp result

I see an undersized heatsink (ok in class d) with 4 transistors bolted to it... (pic is a lil hazy)... if they are 2 pairs, I would check them for shorts.
 
This is going to be interesting... as schematics aren't around yet... hopefully it hasn't folded before pre drive... the voodoo that precedes it most likely will be smd and need a schematic to check wave forms.

You will have to trace the transistors to driver transistors and check them too for shorts

- it would have to have some drive stage but never can be sure with this topology...
 
Have you tried resetting it ? I know you said the fuse keeps blowing which of course suggest a short somewhere but there is a reset procedure in the user manual. If you haven't already, try holding down the PURE DIRECT button and then also press the LOUDNESS button - then release both together and this is supposed to reset to factory default.
 
first check output devices . if any are shorted then check associated components .
is the unit modular ? if so boards might be able to pull out for testing .
 
I wonder - how close is the A-9755 to the A-9555 ? There's a service manual for the 9555 over at HifiEngine with very good schematics. Uses Sanken outputs, 2SA1488 / 2Sc3851 by the look of it.
 
Very sorry to hear about this. One of the reasons I always hit mute before raising or lowering the tonearm.
 
i must be very lucky or the amp in question had a weak spot or not a design that deals with this . i have class d that doesn't seem seem to mind abuse .
at this point in time its anyone's guess as to what is blown . methodical testing is required . i suggest output devices then move on from there .
 
Someone earlier did mention to check spkrs too... seen their shorts knock off amps over the years.

Markoneswift said:
I wonder - how close is the A-9755 to the A-9555 ? There's a service manual for the 9555 over at HifiEngine with very good schematics. Uses Sanken outputs, 2SA1488 / 2Sc3851 by the look of it.
Click to expand...

It appears to be the little brother of the line... chances are topology/layout is the same - maybe smaller power supply/outputs etc... one can hope it answers some riddles in this one
 
Markoneswift said:
Have you tried resetting it ? I know you said the fuse keeps blowing which of course suggest a short somewhere but there is a reset procedure in the user manual. If you haven't already, try holding down the PURE DIRECT button and then also press the LOUDNESS button - then release both together and this is supposed to reset to factory default.
Click to expand...

Yep tried that. No joy.
 
Markoneswift said:
I wonder - how close is the A-9755 to the A-9555 ? There's a service manual for the 9555 over at HifiEngine with very good schematics. Uses Sanken outputs, 2SA1488 / 2Sc3851 by the look of it.
Click to expand...

Pretty much the same just lower power output. I've got the schematics. Thanks for pointing them out :)
 
petehall347 said:
first check output devices . if any are shorted then check associated components .
is the unit modular ? if so boards might be able to pull out for testing .
Click to expand...

I pulled the phono board off to see if was in that section however the amp still did the same thing i.e. broken still
 
If I ever had to deal with this issue once, I've dealt with it 100 times. Back in the 60's and 70's it was a weekly occurrence it seemed. But usually it was a stylus that needed to be replaced, or a tone arm difficulty. Tube amps just didn't blow up. SS state amps like Kenwood, and early units with Germanium transistors would die or put out a puff of smoke]. Early Scotts were very susceptible to failure. Klipsch tweeters instantly failed it seemed. Altec failures were rare. Bozaks never seem to have issue. AR, KLH were usually good to go. Jensen and EV had issues, too. In all the years we sold Frazier, Stevens, Bozak, I just don't remember a failure from a dropped tone arm.

Later as high-powered SS amps came along usually the amps didn't fail, but the tweeters and super tweeters did. Advent, EPI, Boston, B&O, Mcintosh, had their issues. But I think it was from amp clipping more than anything. Mcintosh developing Power Guard saved so many people big money, that we rarely had calls. Arms became semi auto matic which saved money big time,

My tone arm is semi auto matic with auto lift at the end. But every once in a while I mis align the drop on the lead in groove and the stylus will slide off the side of the record. But there isn't any loud noise. Thats one reason I'm very hesitant in buying a VPI Prime Signature with the unit pivot arm. They can get away from you quite easily. I feel the SME 15 with a 309 to be a more secure choice, or Maybe a Clear Audio Ovtation with a TT5.

Having worked at a CW AM radio station in the late 60's the tracking pressures had to be kept around 5 to 7 grams, even with damped tone arms, to prevent daily stylus destruction. SME 3012 Arms were a total failure. When the station was sold in the late 70's long after I left most of the studios still had arms from the late 50's.

Its been close to 10 years now since I trashed my last available Stanton 981 HLZ stylus. Now I'm using a Dynavector 20X 2, and the idea of dropping the tone arm or bending a needle ruffles my feathers and would guarantee big $$$$$$.

I'm sorry for your loss, its going to cost you big time. Maybe its time for some upgrades. A pre-owned Mac with Power Guard. A better more dependable semi auto turntable. And hopefully your speakers came out unscathed. That could be the biggest issue of all.

Let us know if your LP collection needs a new home. I am sure many of us would accept.
 
Mate, start by testing the output transistors as a few have already said, all 4 of them, and any emitter resistors connected directly to them.

Report back before going further.
 
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