Pioneer sx990

[Vrystaat]

Goodday all.
I need some advice plse. I'm working on a Pioneer SX990, but the wiring is a bit confusing on the output stage board. Why do they use two different earth points on the board for each channel.E1 and E2 and E3 and E4 seems to be the same earth point. But if you look on the output board schematic ground 1and3 and also 2 and 4 is split. Can I not just connect ground 1 and 3 together and 2 and 4. This is a bit confusing.
Regards
Jan

 

[Vrystaat]

Sorry, this is what the pcb looks like.

 

[Vrystaat]

Ok so what I mean is if I connect ground 1 and 3 together to form the earth polarity can I test the output board stand alone.
Regards
Jan

 

[rayma]

Should be ok, the separate ground connections serve to reduce ground loops, etc.

Do first check with an ohm meter that they are normally connected together when the amplifier is assembled.
I'm sure that they are.

 

[Vrystaat]

Rayma, much appreciated, All earthing points were connected to earth on the chassis, just not at the same earth point. I started the amp through a 40W DBT and Variac, I did not know what to expect because it was in the hands of another tech before it came to me.The lamp burnt bright but not as bright on a full short. I'll give it a go tomorrow morning.I didn't want to take chance of burning the original Toshiba trannies.

Thanks
Jan

 

[wg_ski]

The grounds for the small signal input section and the ground for the power stage should be returned to the power supply separately. Any small voltage that gets developed across the signal ground wire is effectively in series with the input signal, so you want to keep the current for the power stage out of it. If you tie them together and then return them to the power supply through a common wire you usually see an increase in noise and distortion. Sometimes you get instability.

 

[Vrystaat]

wg_ski,
So that is why the frontend and the power stage were earthed seperately ! Makes sense now, thanks for the explanation !