Author Topic: Repair of Yamaha A-700 amplifier  (Read 301 times)

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Offline Emil88d

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Repair of Yamaha A-700 amplifier
« on: December 06, 2019, 02:20:54 am »
Hello, can someone help me with repairing old yamaha?🤔 I would like to repair this amplifier to learn a Little about electronics but i dont know how to start. When i buy it it has broken transistor 2SC1815 and smoked resistor 1.5k ohm and i replace them and try to power on through lamp and it started then i pluged fuse and the resistor started to burn. I discontcted power source from the main board and measured the voltage on the 2 big capacitors and it was + and - 58,6v
Can someone help me what i need to check more to find what coused burning of the resistor.
I am adding the schematic and the picture where the parts was damaged.
 

Offline PKTKS

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Re: Repair of Yamaha A-700 amplifier
« Reply #1 on: December 06, 2019, 10:22:02 am »
There is no magic or fancy solution here

All discrete boards require testing each component per si

It seems you do have a dead short

A common "fit all"  solution is to power the board
with a variac..  raising it enough to not burn...

But enough (via CC/CV control) to hot spot the dead short culprit
Today thermal cameras are handy..
10y ago we just put  some vapor like fluid or alcohol

your finger sometimes...

Paul
 

Offline PKTKS

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Re: Repair of Yamaha A-700 amplifier
« Reply #2 on: December 06, 2019, 10:32:08 am »

and BTW.. there is a SERVICE MANUAL for this class
which in time was quite complex to diagnose.

It helps a lot with proper check points...

Paul
 

Offline Emil88d

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Re: Repair of Yamaha A-700 amplifier
« Reply #3 on: December 06, 2019, 11:24:24 am »
Ok thank you for targeting me to resolve the problem.👌
 

Offline Emil88d

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Re: Repair of Yamaha A-700 amplifier
« Reply #4 on: December 06, 2019, 04:43:25 pm »
I dont find any hot spots but i started to desolidering end transistors and all at the end are shortcircut and even other transistors at this channel so i think it is not worth to buy all of the transistors.
 


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