SansuiJavier
Active Member
Hello everyone, I would appreciate your help:
I have recap my AU 719, all the electrolytic capacitors (except the big ones 12000/63), black flags, components damaged by the glue and zener diodes. No transistor changed at the moment. I tried it and it comes out protection, I adjusted the bias and DC to correct values. The amplifier works but has a constant electric noise, not very annoying but audible, even with the volume at zero. If I raise the volume increases.
Can someone guide me to find the fault?
I have checked the connections to ground, change the plug, connect it without any source, invert the plug ... still present ..
I have also noticed that the resistors R634-R635 in F3101 seem to have overheated (the amplifier has been in operation only for tests, in total about 15 minutes). These resistors are marked at 68 ohms / 0.5W in the scheme, I replaced them with 68 ohms / 1W of metal film, and it seems that they will not withstand those temperatures. I do not know if it's a problem different from the background noise.
I would appreciate help, what is the probable cause of the noise and how to eliminate it? What points should I check first?
I bought it recently, it had volume crunches and they have disappeared after deoxit, but it also had a "strange" capacitor that was added in some previous careless repairs..
Thanks in advance
Javier
F3101 resistors:
my 719 in the operating room:
I have recap my AU 719, all the electrolytic capacitors (except the big ones 12000/63), black flags, components damaged by the glue and zener diodes. No transistor changed at the moment. I tried it and it comes out protection, I adjusted the bias and DC to correct values. The amplifier works but has a constant electric noise, not very annoying but audible, even with the volume at zero. If I raise the volume increases.
Can someone guide me to find the fault?
I have checked the connections to ground, change the plug, connect it without any source, invert the plug ... still present ..
I have also noticed that the resistors R634-R635 in F3101 seem to have overheated (the amplifier has been in operation only for tests, in total about 15 minutes). These resistors are marked at 68 ohms / 0.5W in the scheme, I replaced them with 68 ohms / 1W of metal film, and it seems that they will not withstand those temperatures. I do not know if it's a problem different from the background noise.
I would appreciate help, what is the probable cause of the noise and how to eliminate it? What points should I check first?
I bought it recently, it had volume crunches and they have disappeared after deoxit, but it also had a "strange" capacitor that was added in some previous careless repairs..
Thanks in advance
Javier
F3101 resistors:
my 719 in the operating room:
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