A-757 Speaker relay make a "buzz" or is it?

[Ljudex]

When I switch on the amplifier it takes a while before the speaker protection relay is stabilised in "on" mode.
During that time a buzzing sound kan be heard in the relay area?

I bought two new relays (Omron) and replaced them old ones as they could be the issue due to several tips on the internet.

But no change... what's next to try a cap or two?

Any tips is appreciated !

 

[Ljudex]

No one..?

 

[petehall347]

do all relays buzz ? am taking a guess answer is yes . i am thinking its a power supply issue . bad smoothing capacitor or bad rectifier for relay power .

 

[larryderouin]

Either the supply cap or relay switching transistor(s) on the protection board is bad.

 

[Ljudex]

Do you mean this board for both cap and transistors?

 

[petehall347]

i couldn't figure out where the power comes from for relays .

 

[Ljudex]

 

[petehall347]

i have the diagrams already but am failing to see where the power comes from for relays . will check again as it was late last night

 

[Ljudex]

Cool thank's for the support!

 

[petehall347]

ok .i would change all 6 electro caps in regulator first . if that doesn't fix it start looking at relay driver transistors .

c623
c624
c621
c622
c605
c606

bur first look at ac and dc voltage pin 1 of the 5 pin plug .speaker term assembly .

 

[Ljudex]

Yeah, I just spoted them on the diagram, now you confirmed my own ideas, but I was not 100% sure thank's!

 

[Ljudex]

Well I replaced the six caps and it went back to normal, but.....now it's back again and worse sometimes it can take up to 5 minutes before it starts to play anything.
And now have all the red lamps gone black as well.