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Old 26th June 2012, 01:11 PM   #1
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Default Sansui G5700 Heat Problem

Hi
I recently purchase a Sansui G5700 receiver, everything works fine, but I worry that gets very hot in the heatsink of the power transistors even at low volume, including several small transistors as well as hot, I never read that talk about the sansui class of amplifiers class A, B or AB, is this normal or do I need to adjust the bias current that goes to 5 volts. I only use 2 speaker at 8 ohm I am planning to put 4 that it increase the heat.
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Old 26th June 2012, 02:04 PM   #2
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Default Adjust 3.3 milivolts into these points you see

The output line and the power transistor's emitters..... the voltage drop over the output resistors.

This way it will be not even warm to the touch.

You may be adjusting or measuring wrong place....because correctly adjusted, the iddle power is too much small to you to feel heat into your heatsinks.

You may have other kind of troubles in your circuit.... not only bias adjustment..... but first step is to be sure each power transistor will have a voltage drop of 3.3 milivolts DC in stand by mode (without audio).... this represents 540 miliwatts of heat in each power transistor...this cannot be so big heat unless you have 40 output transistors.... and for sure you have not all these folks there.

Good luck,

regards,

Carlos
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File Type: jpg Not even warm.jpg (732.7 KB, 62 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg

Last edited by destroyer X; 26th June 2012 at 02:09 PM.
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Old 26th June 2012, 02:25 PM   #3
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Default Check your adjustment.... if you continue to face troubles, then

search for our forum friend Sakis.....he is skilled to fix these kind of amplifiers.

regards,

Carlos
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File Type: jpg Bias adjustment.jpg (801.7 KB, 57 views)
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 26th June 2012, 02:26 PM   #4
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Thanks destroyer X

I did the measurements and I noticed that the left channel is on 53mv and continues to increase as temperature up to 90mv, R is 3.3mv and up to 10mv.

I have a bad copy of service manual is possible you send me a better one? my email- mc_tech@yahoo.com

Thanks Carlos

Fernando
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Old 26th June 2012, 03:06 PM   #5
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Default 53 milivolts is a lot .... too much, this represents almost 10 watts

to each of your transistors....reduce it to 3.3 milivolts as soon as possible.

I will send the Service Manual in pdf.

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 26th June 2012, 03:13 PM   #6
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Default Too much big Service Manual to send to you

But you can download it here:

Download Manuals for Free -- Sansui G-5700 Receiver

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 26th June 2012, 05:19 PM   #7
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Hi Thanks destroyer X

I follow yours instructions and Problem is solved THANKS TO YOU and for a service manual

Thanks !!
Fernando
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