Hifonics Saturn X

[Bertje]

I have a Hifonics Gen X Saturn 4 channel for repair.
One channel has 500mV dc offset, adjustment is possible but gives 200mV at minimum. Plays normal audio but on high level the sinewave become assymetrical, not good...

So I think something is wrong, measured all transistors on the mainboard (ok), could be the vertical card with the diff stage the problem..? Or other known issues with this Gen X amps?

Hifonics Saturn X

 

[Perry Babin]

Does it have offset adjustment pots as well as bias pots?

The differential stage is a prime suspect if the defective channel will produce clean audio to full power into its lowest rated load.

 

[Bertje]

It has one pot, bias is not adjustable (measured). Without load there is dc offset, sinewave is shifted vertically 500mV. With a 4 ohm load the same behaviour.

 

[Bertje]

After swapping two identical driverboards (chl 3 and ch4) the fault persists on the same channel. So the driverboards with the differential amplifiers were ok.
Removed a few transistors from ch4, and one drivertransistor was defect (one open pn): 2sc2238. Was not measurable in circuit.