Yamaha AX-550RS - toasted fuse reistors

[Karl vd Berg]

G'day to all,

I was given back an Yamaha AX-550RS amp that I sold to a guy in February of this year.

The guy bought a new amp and wanted to through this away. So I intervened. Took it home.

The problem is that "it smoked and stopped functioning", according to him. At home I open it and saw two green resistors (near the white resistors) toasted.

Bias issue? Drivers short? He said that used to play it VERY LOUD FOR MANY HOURS using a set of 8 speakers connected I don't know how!

Anyway, pictures below:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

The resistors were originally green coloured like these ones:

An externally hosted image should be here but it was not working when we last tested it.

Is it just an fuse resistors issue?

 

[Karl vd Berg]

No inputs?

 

[east electronics]

KARL ...
the input you give is too low state the part number i will check with my data base and according to schematic and let you know what have i recorded from previous repairs on this model .

Kind regards
sakis

 

[basi]

Those are R151,152 Resistor on service manual...22 ohm on negative power supply line feeding input and pre drivers transistors.You can replace them with higer watage type,also check C130,131 capacitors 470 uf 63v.
Good Luck!!!

 

[Karl vd Berg]

KARL ...
the input you give is too low state the part number i will check with my data base and according to schematic and let you know what have i recorded from previous repairs on this model .

Kind regards
sakis

Thanks Sakis!

I suspect that the previous owner put more speakers in parallel (8 speakers he said) lowering the impedance to less than 8 ohms, or even less than 4 ohms, I don't know. He used to play the amp very loud for many hours!!

 

[Karl vd Berg]

Those are R151,152 Resistor on service manual...22 ohm on negative power supply line feeding input and pre drivers transistors.You can replace them with higer watage type,also check C130,131 capacitors 470 uf 63v.
Good Luck!!!

Ok, thanks!! Might be a good idea to check if the drivers are short? I hope not.

 

[basi]

Ok, thanks!! Might be a good idea to check if the drivers are short? I hope not.

Yes of course check the drivers and predrivers.I forgot to mention that.