Technics SU-G90 no display or sound

Tony Howlin · 7th May 2008, 07:15 PM

Hi!,
This unit had intermittent output and I tried to help a friend by expecting to find dry joints. I found a few, but the fan was not working so while I was tracing the circuit my hand slip and I now have no display or audio. I have voltage on pin 4 60volts and lights on the function buttons. Q705 transistor seems to run hot as the circuit board is discoloured. I have no schematic and would appreciate any help I will give more info if needed. Looking forward to someone pointing me in the right direction.
Thank you
Tony

312capri · 30th October 2010, 04:56 PM

My sons each purchased a Technics system which included these power amps. Both amps have the same problem with intermittent audio and display. Anyone have any ideas of whats causing the problem?

sakis · 30th October 2010, 06:11 PM

i only have available su-g 91 schematic and you are welcome to have it .... just e mail me ... Please notice that most of these models have a circuit with ventilator with a sensor ...meaning that if the speed of the fan is low for any reason of failure or simply cause the fun is broken the amp goes on protection mode

in your case obviously there is going to be more than that.... I epect schematics to be the same only 91 might be more powerfull

kind regards sakis

312capri · 30th October 2010, 06:24 PM

The fan circuits in both amplifiers work. It appears the problem exists within the connections between the front panel and the main mother circuit board. It must have been a common problem because both these power amplifiers exhibit the same condition. If you tap on the box the interment goes and comes back! I am wondering if anyone else has found the source of the problem?

7th May 2008, 07:15 PM	#1
Tony Howlin diyAudio Member Join Date: May 2008	Technics SU-G90 no display or sound Hi!, This unit had intermittent output and I tried to help a friend by expecting to find dry joints. I found a few, but the fan was not working so while I was tracing the circuit my hand slip and I now have no display or audio. I have voltage on pin 4 60volts and lights on the function buttons. Q705 transistor seems to run hot as the circuit board is discoloured. I have no schematic and would appreciate any help I will give more info if needed. Looking forward to someone pointing me in the right direction. Thank you Tony

30th October 2010, 06:11 PM	#3
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	i only have available su-g 91 schematic and you are welcome to have it .... just e mail me ... Please notice that most of these models have a circuit with ventilator with a sensor ...meaning that if the speed of the fan is low for any reason of failure or simply cause the fun is broken the amp goes on protection mode in your case obviously there is going to be more than that.... I epect schematics to be the same only 91 might be more powerfull kind regards sakis __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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30th October 2010, 04:56 PM	#2
312capri diyAudio Member Join Date: Oct 2010	My sons each purchased a Technics system which included these power amps. Both amps have the same problem with intermittent audio and display. Anyone have any ideas of whats causing the problem?

30th October 2010, 06:24 PM	#4
312capri diyAudio Member Join Date: Oct 2010	The fan circuits in both amplifiers work. It appears the problem exists within the connections between the front panel and the main mother circuit board. It must have been a common problem because both these power amplifiers exhibit the same condition. If you tap on the box the interment goes and comes back! I am wondering if anyone else has found the source of the problem?

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