Sansui Alpha AU-907i MOS Limited

[AlphaAudio]

Ok.
Left channel:
Tran. #1 34.6mV
Tran. #2 21.9mV
Tran. #3 26mv
Tran. #4 31.4mV
Tran. #5 25mV
Tran. #6 25.3mV
Tran. #7 -23.7mV
Tran. #8 - 16mV

 

[Bernhard]

Strange, before to ground tran 6 was only 5mV...

Tran. #6 R +1.57V L (-65)-(5)mV jumpy

That looks all ok, is this the hot side ?

 

[Bernhard]

How is the right channel, measured like this ?

 

[AlphaAudio]

Right channel: with Cold reference
Tran. #1 -21.6mV
Tran. #2 -24.8mV
Tran. #3 25.4mV
Tran. #4 20.7mV

 

[AlphaAudio]

Post #62 Yes Tran. #6 is on the hot side.
On both sides Tran. #6 is on hot side.

 

[Bernhard]

Right channel: with Cold reference

And hot ?

 

[AlphaAudio]

Hi Bernhard, Here is nearly 1am I think that I will take a break and continue tomorrow. Going to sleep 🙂 Really thank you for everything. I really appreciate your help. Hope to have conclusions with those tests.

 

[Bernhard]

That looks all ok, is this the hot side ?

I meant: is L the channel where the heatsink is much hotter ?

 

[Bernhard]

Hope to have conclusions with those tests.

Yeah, on the right channel you measured only the 4 transistors on the cold side, we need hot side too.

 

[AlphaAudio]

I have problem to reply to the posts. I opened a case the support diyAudio.

To do the same with the hot on Tran. 5-8 on both channels?

 

[Bernhard]

you did 1-8 on left but only 1-4 on right

 

[Bernhard]

So we still need 5-8 on right

 

[AlphaAudio]

Ok.
Left channel: hot side
Tran. #5 22.1mV
Tran. #6 22.7mV
Tran. #7 -26.4mV
Tran. #8 -18.5mV

Right channel: hot side
Tran. #5 67.4mV
Tran. #6 2.7mV
Tran. #7 -26mV
Tran. #8 -44.6mV

 

[AlphaAudio]

The temperature on the heatsink rises to 58°C on right channel hot side

 

[Bernhard]

Thanks, now I'm a little confused.

Before when measuring to the ground, on the left channel tran 6 only had 5mV:
Or did you mix up the channels ?

Left channel:
Tran. #1 R - 1.58V L (-55)-(50)mV jumpy
Tran. #2 R - 1.59V L (-45)-(60)mV jumpy
Tran. #3 R +1.8V L 50-120mV jumpy
Tran. #4 R +1.85V L 74-110mV jumpy
Tran. #5 R +1.65V L (-18)-(45)mV jumpy
Tran. #6 R +1.57V L (-65)-(5)mV jumpy
Tran. #7 R - 1.83V L (-152)-(-82)mV jumpy
Tran. #8 R - 1.87V L (-90)-(-30)mV jumpy

Now the right channel tran 6 only 2.7mV which looks like something wrong either Fet or resistor.

 

[Bernhard]

The temperature on the heatsink rises to 58°C on right channel hot side

The upper heatsink ?

 

[Bernhard]

So, on the right channel there is nearly no bias / current on FET 6

 

[AlphaAudio]

Yes. The upper heatsink is the right channel

 

[Bernhard]

Tomorrow measure the resistor behind FET 6 if it is ok or open

Just turn the amp off, keep the black clip on the pin and the red one on the left fork of FET 6. And measure ohms.

 

[Bernhard]

Left channel: hot side
Tran. #5 22.1mV
Tran. #6 22.7mV
Tran. #7 -26.4mV
Tran. #8 -18.5mV

Right channel: hot side
Tran. #5 67.4mV
Tran. #6 2.7mV
Tran. #7 -26mV
Tran. #8 -44.6mV

Right channel: hot side
Tran. #5 67.4mV
Tran. #6 2.7mV
Tran. #7 -26mV
Tran. #8 -44.6mV

You see what I see ?