Phototone
Super Member
I have acquired a Sansui AU-517 integrated amp, and I downloaded a PDF of the service manual. It has the procedures for setting the bias and DC offset of the amp.
Well, following the procedures I am able to easily set the DC offset to near .0 mv. reading from the speaker terminals as indicated.
Now, for setting bias, there are 2 test pins (+, -) that you are to connect your voltmeter to, and another pot to adjust. Bias is supposed to be set at 20mv.
I can't get a reading from either set of test pins. (one set per output block) They read 0. Turning the bias pot does not change this, so I left the bias pots about mid range. The amp plays nicely, and the output transistor heatsinks are almost cool to the touch, one is just a wee bit warmer, but nowhere near warm. The power supply caps are cool, the dual power transformers are just a wee bit above room temperature..so no obvious "issues".
I am very puzzled about the inability to get a reading. I know my voltmeter works because I can use it to set the dc offset down in the same millivolt range.
Does anyone have an idea?
Well, following the procedures I am able to easily set the DC offset to near .0 mv. reading from the speaker terminals as indicated.
Now, for setting bias, there are 2 test pins (+, -) that you are to connect your voltmeter to, and another pot to adjust. Bias is supposed to be set at 20mv.
I can't get a reading from either set of test pins. (one set per output block) They read 0. Turning the bias pot does not change this, so I left the bias pots about mid range. The amp plays nicely, and the output transistor heatsinks are almost cool to the touch, one is just a wee bit warmer, but nowhere near warm. The power supply caps are cool, the dual power transformers are just a wee bit above room temperature..so no obvious "issues".
I am very puzzled about the inability to get a reading. I know my voltmeter works because I can use it to set the dc offset down in the same millivolt range.
Does anyone have an idea?
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