Musical Fidelity X-A2 help!

[27AUDIO]

Hi all, I have on my bench work a Musical Fidelity xa2 with power transistor fault and I'm waiting for a new pair of SAP15PY and SAP15NY for replace.
The problem will be the setting of bias.
Anyone can help me to fix the bias point? I can't found the service manual.

Thanks very much

Sergio

 

[2quad]

Service manuals for Musical Fidelity is not easily available!

Just from the top of my head I guess you will find large emitter resistors close to the power transistors. See if you can read the values on those resistors. The voltage across these will tell you the quiecent current, using Ohm's law. Anything between 30 and 80 milliamps should be OK. Allow the amplifier to heat up before the final adjustment.

EDIT: Those resistors are inside the transistors. The data sheets states 40 mA as optimum quiecent current. I guess the two small trimmers on the PCB is for this adjustment.View attachment sap15.pdf

 

[27AUDIO]

Ok, so I can use test point E and S pin, and measure voltage accros it.

 

[2quad]

Yes, you should measure 8,8 mV between E and S, and/or 17,6 mV between S and S.

 

[27AUDIO]

Thanks very much!
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