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Old 18th May 2010, 04:54 PM   #1
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Default Concept 16.5 Issues.

Good day all,

I have a Concept 16.5,

Great old receiver, I love it. Recently a problem has been occurring. The volume can be at ANY level, low, medium, or loud. All of a sudden I get a quick and very loud buzzing sound over the speakers(less than 1 second long). The receiver then kicks into protection right away, then it kicks back out of protection mode(maybe 3-4 seconds it sits in protection) and continues to play the tunes like nothing has ever happened. Other than this the receiver has absolutely no background noise or hum, the bass is so tight and defined it's unreal, this receiver makes an old set of 30 watt hitachi's sound like gold.

I made sure all connections, grounds etc are tight inside, ridded of the dust, quadruple checked my speaker connections etc.

So does anyone have any insight as to why this might be happening? Some extra info before I bring it down to the repair shop would be great.

Also any info on Concept gear in canada? i'm in Northern Ontario, had never seen any Concept gear until I found the 16.5, which would have went to the dump the very next day. Been enjoying it for a while.

Sometimes the problem occurs after a day, sometimes it takes 1-2 weeks to happen....

Thanks and have a great day!
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Old 18th May 2010, 05:25 PM   #2
infinia is offline infinia  United States
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Hi
I have a 11.0 I had repaired one channel by replacing most all transistors in the power amps section except the front end pair. Then after the repair I would get somewhat the same symptoms as yours except a load pop and everything else the same re protection and reset on again. I ignored it it, until one time it never came back on again. Back at the bench I saw all the same new transistors were shorted again. I'm acquiring new sets of transistors and will replace the frond end diff amp as well. I'm almost positive the original problem can traced to them going leaky due to age and heat. I would recommend that you have each channels diff amp pairs replaced as soon as possible before yours blow. If they blow the 16.0 transistors are almost impossible to find. If you do find them, the parts alone cost close to $100 US just for one sides TO-3 outputs and drivers.
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Old 18th May 2010, 05:51 PM   #3
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Thank you for the advice infinia. I'll tell my tech about it, thanks again!
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Old 18th May 2010, 09:32 PM   #4
sregor is offline sregor  United States
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Maybe unrelated, but used to see it in Nikko receivers - broken ground connection where the leads came into the amplifier PC would cause the outputs to "float" and put some DC on the output. The leads were on a plastic slide type connector, and you could see the broken solder on the back side of the board move when you moved the lead. Also, we used to see amplifiers where the ground to the amp was through a screw which was loose, causing intermittent hum and protection circuits firing - mostly on some of the late 70's Akai and JVC receivers. Just a shot.
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Old 18th May 2010, 11:21 PM   #5
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Quote:
Originally Posted by infinia View Post
Hi
I have a 11.0 I had repaired one channel by replacing most all transistors in the power amps section except the front end pair. .
Transistors dont blow up for no reason.
Problems can be down to oscilation or simple bad design.
It might be worth looking at the transistor specs to see if the yare correct voltage etc.

I would also be looking at the output for oscilation.
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Old 18th May 2010, 11:29 PM   #6
infinia is offline infinia  United States
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Quote:
Originally Posted by nigelwright7557 View Post
Transistors dont blow up for no reason.
Problems can be down to oscilation or simple bad design.
It might be worth looking at the transistor specs to see if the yare correct voltage etc.

I would also be looking at the output for oscilation.

Design is good if you don't consider all devices need Y code parts, but personally I would NOT do any sinewave full power testing at 4 ohms.
Works fine just random loud pops. I suspect LN front end devices are just going leaky. That s/b cause for complete meltdown.
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Old 18th May 2010, 11:30 PM   #7
spind is offline spind  Canada
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You may want to search around on AudioKarma a bit---there is quite a bit of Concept information on that site (perhaps even some service info).

Good luck,
Steve.
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