Aleph 2 construction problem!

[alexmark]

Hi,

I've just tested my second channel of my Aleph 2(connect with speaker and source) but I suspect there is a short on my main board cos there is no sound coming out from the speaker but -50V at my speaker output terminal!!!

some observation,
1.while powering up the -Ve rail voltage reading come up very slow and discharge faster if I compare to +Ve rail.(I've power up 5 time and getting the same result.---> -50V at output terminal)

2.I've checked the power supply, which is O.K.

3.there is no components smoke or even getting hot.(only power up 5 sec)

I'm pretty sure that all the component and connection is O.K. cos I've tested this channel before without connect to the speaker and the output offset voltage around 15mV.

Action....
What things I need to check first.


Another Channel is running well, I've making some measurement on it.

supply voltage is around +/-50V.
1.Q3 Drain +3.84V
2.Voltage across R14 392, 4.52V.
3.Q5 Vce, 4.42V.
4.12 output mosfet source resistor, 0.389V
5.Temp measure from the centre of the heatsink is around 60C (ambiet at 30C)

Is the voltage reading acceptable? The voltage across the Source resistor seem to be a little low only 0.389V instead of 0.5V, Why? Do I need to adjust it to the right voltage, how to increase it?

Any comment and help would be greatly appreciated.
photo of my A2 .. http://www.diyaudio.com/forums/showthread.php?s=&threadid=6730

thanks,
alex

 

[Nelson Pass]

Probably your main current source is OK, but either your
differential / feedback is broken or your negative output
devices are broken / miswired.