Analogic Sound

Analogic Sound

ONKYO integra A-8760 hi-fi amplifier r&r project

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This is a nice new r&r project of a high quality power amplifier (made in japan) ONKYO integra A-8760, a beast from the late 80’s !

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There is a whole story about how I got this amplifier, it was offered as a gift, non-working unit, spare parts only, you name it. One thing was for sure, it has 14kg and as far as I could see it didn’t have any noticeable plastic parts, it may sound funny but these are the best things you should consider on an amplifier(or other product if you ask me), you don’t have to be an audiophile or whatever, just take your weighing device with you and that is it! 🙂

“Under the bonnet” I found a huge linear power source with a nicely shielded transformer and two big caps, that is the heart of any amplifier and it matters a lot, it is like the engine of a car, the bigger it is, the better it sounds 🙂

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The tuning age is at it’s best, just look what a nice upgrade I found inside this amp, a led bar and a couple of fans, they hit the dumpster in no time!

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The amp powered on but there was no output from speaker terminals, I noticed some burned electronic components, let the fun begin! Take a look at the main fuse that I found, can’t be bigger than this :

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As you are already familiar with analogicsound’s projects this project also required the service manual, it was absolutely necessary. Of course that huge power source was ok(even if inappropriate fuses were used) , in fact the amplifier powered on just fine, the problem was not in there. If you replace a fuse with a good one and it blows again you should never install a bigger one(or a golden one 🙂 ), that is just stupid and can add extensive damage to any device, you just have to repair that device or use the dumpster.

I must say that this amp suffers from cracked solder issue, a lot of devices from the 80’s and 90’s suffer from this, age is age and bad solder issue is indeed a huge source of problems, I decided to resolder all components, the preamplifier was badly affected but other modules had problems also.

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After this time consuming job there were no big improvements, almost all transistors from the final stage were shot, a lot of power resistors were damaged also, most of them read high impedance, further analysis were necessary. A big problem is that original transistors (made by Sanken) in Japan are hard to find, of course cheap chinese components are always on the market but for this amp I wanted the best transistors “made in japan”, no budget repair!

This is gold(thank you @brain 😉 )!

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One thing that I love about this amplifier is that is quite serviceable. It has separate modules and a lot of space between components, no SMD, high quality capacitors and high quality japanese design from the golden age of hi-fi, it is a pleasure to work on it!

Here are the final stage transistors:

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All final stage transistors were replaced (as pairs) and all related components were checked and replaced if necessary, biggest problem were out of range components, like resistors who suffer a lot when  a short circuit is happening, this resistor supposed to be 2.2kohm and now it reads almost 3kohm:

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Various replaced components:

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After all these steps the amplifier was ready for tests, DC voltage protection was checked and idle current was adjusted within specs.

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Then the speakers were connected, normal operation and all functions&inputs were tested, the repair was a success!

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Thanks for reading, more r&r projects will be available soon, the project will be advertised on facebook, thanks to all who liked this !

 

 

 

 

 

Written by admin

July 20th, 2016 at 8:47 pm

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