aleph 5 no bias

[karajak]

My finiss version of aleph 5 refuses to start (left channel).
Right channel is fine ,measurments according to manual.
On left channel there is no bias across R64-66 and R40-42.
Z5 9,1 V.
Q5(BC550C) no voltage across E and C.
Q4 3,66 V across E and C.
Output dc offset 78 mV.
On speaker only ham.
Any help ? Thanks and MERRY CHRISTMAS to all of you !

 

[Zen Mod]

Merry Christmas to you too!

Can you share some pictures and your referent schematic with us , in Spirit of Christmas??

 

[karajak]

I am referring to the original schematic by Pass.I am trying to upload some photos. Thanks ZEN.

 

[karajak]

 

[Zen Mod]

see several measurement values

where you see main difference ?

 

[Zen Mod]

also study this one , pretty much everything shown

 

[karajak]

Z5 9,1 V.
Q5(BC550C) no voltage across E and C.
Q4 3,66 V across E and C.
Output dc offset 78 mV.

 

[karajak]

On left channel there is no bias across R64-66 and R40-42.

 

[Zen Mod]

instead of R11 put trimpot 100R plus 120R fixed resistor (these two in series , preset to max - 220R)


instead of R19 , put 120K fixed and 100K trimpot ((these two in series , preset to max - 220K)

 

[batteryman]

Z5 9,1 V.
Q5(BC550C) no voltage across E and C.
Q4 3,66 V across E and C.
Output dc offset 78 mV.

If Q5 is short circuit this will switch off the upper mosfet and as there is no voltage drop either it is short circuit or there is a short on the pcb. (base to emitter or emitter to collector)

What is the voltage on Q5 collector with respect to 0v?

 

[karajak]

Hi everyone ! I wish a happy new year to you all.
After the Christmas vacation I checked everything again and ...miracle... I discovered that I forgot to solder R20 resistor .Its amazing that after adding that everything is OK .
The sound is fantastic and I want to thank all members who replied.

 

[Zen Mod]