Yamaha A760 II - No sound

idiota

idiota

Member
So i got another A-760II Yesterday, but there's no sound out of it, and the headphones doesn't work either. In curiosity i plugged in a set of active speakers to the headphone output and there's faint sound coming from it. The sound seemed to be affected by the preamp controls (balance, bass, loudness, etc) however it's so faint. Any ideas whats wrong with this amp? Thanks in advance :)
 
Its either sensing DC at the amplifier output and staying in protect mode--shorted output or driver transistor(s)
Or.. You have a power supply/protect circuit problem---Bad solder/broken connection/dried up capacitors/fuses/fuseable resistors/transistors/diodes/etc.
 
avionic said:
Its either sensing DC at the amplifier output and staying in protect mode--shorted output or driver transistor(s)
Or.. You have a power supply/protect circuit problem---Bad solder/broken connection/dried up capacitors/fuses/fuseable resistors/transistors/diodes/etc.
Click to expand...

ah well that seems like a whole lot of things to check :scratch2:

fuseable resistors.. are they the blue resistors on the main power amp board?
 
idiota said:
ah well that seems like a whole lot of things to check :scratch2:

fuseable resistors.. are they the blue resistors on the main power amp board?
Click to expand...

They are usually mounted up away from the board perhaps 1/4".Blue-greenish.
 
idiota said:
what do you mean with "mounted up away from the board"? and where are the output resistors? thanks :)
Click to expand...

I mean they are soldered to the board but there standing away from the board.. look at photo for example of two possible scenarios.
 

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idiota said:
what do you mean with "mounted up away from the board"? and where are the output resistors? thanks :)
Click to expand...

Output transistors

Are fastened to the Large aluminum heatsinks. MT-200 Sanken's I think..
 
idiota said:
is it possible that the relay won't "click" because it's dirty?
Click to expand...

Anything is possible..But I rather doubt it. Bad solder connections in the 12v regulated power supply could also be a issue.
 
Hey all, sorry for the long gap between posts. I've been busy with tests and getting sick a lot lately so i don't really have much time to tinker with the Yamaha Amp.. I got better recently so i checked it up again..

I've desoldered the output Sankens and checked them with a multimeter, and they are not open or shorted.. So i guess they are not the problem.. this leaves the fuseable resistors, power supply, and driver transistors.. which one is more likely to check first and what to check in the power supply? thanks in advance :)
 
I've desoldered the output Sankens and checked them with a multimeter, and they are not open or shorted.. So i guess they are not the problem.. this leaves the fuseable resistors, power supply, and driver transistors.. which one is more likely to check first and what to check in the power supply? thanks in advance
Click to expand...

Have you already reinstalled the output transistors?
 
avionic said:
Tr327-330..
Click to expand...
Are they located in the part of the main board that is obscured by the phono preamp board? I can't remove the phono preamp board yet. There's 4 screws that won't come out. Should i use WD40 or something like that?
 
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