Sony STR-4800 Help

[Darkvalley]

Hi
Well, short-lived joy following the discovery of this amp found this morning.
Functional, various conclusive tests (including speaker suicides). I turn off, disconnect, and install an antenna to test the FM, and then nothing.
Apart from putting an antenna, I haven’t touched anything.

The symptoms:
No more sound except by turning the volume to 3/4 and it "spits" into the speakers (all types of inputs)
The Low Filter button causes the relay to trigger for a fraction of a second.

I suppose, maybe wrongly, a problem with the preamp. Why on earth does the button lock the relay for 1/2 second?

Thank you sincerely for your help.
Kinds rearads
Laurent (France)

 

[Darkvalley]

 

[Richard P]

Check the fusible resistors R911 & R912 in the power supply section. They are prone to failure for no apparent reason. . . . Look for and replace other fusible resistors while you are in there.

 

[Darkvalley]

Hi
Thks for your message.

I will look into this and get back to you.

 

[Darkvalley]

 

[Richard P]

Yes. R912 on the negative supply rail and R911 on the positive supply rail,

 

[Darkvalley]

Hi
Indeed, R911 is faulty.
I checked Q931 and D931; both are functional.
Must I use fusible resistors, or can I use standard resistors instead?

 

[mbz]

Yeah, fusibles are increasingly difficult to find (Yageo FKN series?)

Replace with whatever you can find but must be same wattage, flame rertardent coating, mounted raised off board for cooling

 

[Darkvalley]

Thank you very much !

 

[Richard P]

I use standard metal film resistors with the same power rating. . . .