Wow.. Yes you are right. I don't know from where I got this value but I will fix it right away. Thank you.
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Marantz 1515 lights / lamps....
- Thread starter kyle775
- Start date
I don't know if that is right? I think what it means is that you have a slight positive voltage bias which I think would help in the switching from positive to negative part of the waveform minimizing the 0 point crossover distortion? If you set the offset to the negative values by making the neg voltage equal to 4.7mV, I think it achieves the same purpose to move the zero crossing switchover off of 0v. Does it sound any different? I tried to find another receiver in the same family, but the next one up 1520 has the same instructions and the 1550 has a different discrete Main Amp board.
Ok. Thank you.
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Oh.. Why you are saying that? I really respect you.
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Sorry but I didn't understand you.
Ok. Anyway. Thank you for everything you did for me till now I really appreciate you help and accept my apologies if I said something wrong because I don't think that I did.
BTW Sensei in Japanese or Chinese it's a title of honor and respect to someone who is teaching you.
My heritage is 3rd generation Japanese so I am aware of Sensei.
This may be getting more technical than you want, but I looked up the part for Q701/Q702.
FYI, this is the amp that is used in your Main Amplifier, LM381. If you compare the typical application on Page 2, it looks very similar to your amplifier.
The LM391 drives the pair of transistors for the output.
Note that there are two resistors RE and RE' which corresponds to your R741/R743 on your board.
On page 7, the paragraph describes how to adjust "bias current" by measuring the voltage across resistor RE. It says to adjust "RB" on Figure 1 to provide about 25mA of current. We calculated 10mA = 4.7mV, so we can actually go a little higher (according to the datasheet).
Recommendation: I would go back to your original adjustment of 10mV across the resistor R741 and R742 and leave it at that.
This may be getting more technical than you want, but I looked up the part for Q701/Q702.
FYI, this is the amp that is used in your Main Amplifier, LM381. If you compare the typical application on Page 2, it looks very similar to your amplifier.
The LM391 drives the pair of transistors for the output.
Note that there are two resistors RE and RE' which corresponds to your R741/R743 on your board.
On page 7, the paragraph describes how to adjust "bias current" by measuring the voltage across resistor RE. It says to adjust "RB" on Figure 1 to provide about 25mA of current. We calculated 10mA = 4.7mV, so we can actually go a little higher (according to the datasheet).
Recommendation: I would go back to your original adjustment of 10mV across the resistor R741 and R742 and leave it at that.
By the datasheet of the LM391 25mA should give11.75mV. I've tried to figure out the temp before and after the changes on some of the parts on the board like the resistor and the transistor with heatsink in the attached pictures and the deferences is few degrees. Again, do you think that there's an error in the service manual and instead of 10mA it should be 10mV? Thank you.
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Based on what we now know, I would think that the SM has an error. The procedure says to use a Voltmeter and a specific voltage range setting, but the adjustment value seems to have the wrong units. The NS LM391 datasheet instructions for adjusting the bias current to 25mA seems to match the value of 10mV pretty closely. I would keep it at 10mV across the resistor.
The Also, when taking the voltage measurement, make sure the selector is in AUX and volume control is turned all the way down.
The Also, when taking the voltage measurement, make sure the selector is in AUX and volume control is turned all the way down.
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Yes that's right! And yes of course it was all the time on zero volume and on AUX when nothing was connected in the inputs. That's why I wrote this question on thread #50 if it's 10mV instead of 10mA. Thank you very much for your help.
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BTW related to the post on https://audiokarma.org/forums/index.php?threads/marantz-1515-dc-offset-bias.530943/
When I adjust the R717 the value on both resistors R741+R743 change simultaneously while R741 is positive and R743 is negative but the values are very close or the same. R718 doesn't effect R743 because it is on the other channel.
When I adjust the R717 the value on both resistors R741+R743 change simultaneously while R741 is positive and R743 is negative but the values are very close or the same. R718 doesn't effect R743 because it is on the other channel.
