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Erratic volume on Technics SU-X911 amplifier (Class A)

Hello, was wondering if someone could advise on this problem ... Background: My midi Amp (SU-X911) is part of a Technics system (CD player, Tuner, Cassette Deck, Equalizer). The system was bought sometime in the late 80's (yes it's old). Problem: Amp volume (controlled by electronic dial) DANGEROUSLY ERRATIC - suddenly silent for 2-3 seconds, before jumping to almost max! Adjustment to volume control brings it back to normal volume. During the silent and max jump, the volume level display (eg. "-44dB") does not change. Consequences: My precious speakers risk being blown up! Remedy attempts so far: Following advice from an electrician colleague, I've pulled apart the amp, pulled out the volume control potentiometer and spray cleaned it (with electronic spray). I must say the amp was generally very very clean inside. Success? - No, problem returned after one day of amp operation. Other Notes: My colleague now suggests it could be the amp itself playing up (ie. not the volume pot). I listened to a whole CD (45mins) last night, and did not encounter the problem - interesting to see if the problem occurs using headphones as well as the speakers themselves. Any ideas anyone? Would greatly appreciate advice - perhaps there's one bit of the amp I need to look at / replace. Thanks!!!

Posted by aranciata-oz on

  • babiuk Aug 30, 2008

    Hello, I´ve got the same problem in the same amp, it sounded ok till one day it begun to mute itself randomly and jump to high volume in the next minutes.
    A month ago the problem turned into playing normal for a few minutes and after that I just got silence.
    And nowdays it doesn´t sound anymore.
    I tried to use the headphones... but nothing.

    Please tell something about if you´ve got solved it.

    Thanks
    and excuse my bad english.

    Bye!




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Anonymous

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I have a technics su x911 linked to ars x911 and a sl pj26a and a st x 933l tuner and turntable, they are all linked to each other as is typical however, I can turn the amp on,the red light shows on and everything else will work but not the amp.there is no led display and no vulume control.

the set has not been used for many years but has been kept clean and dry.
do they have to be connected in a certain order, the remote control doesnt seem to make any difference.

Posted on Aug 19, 2009

  • Audio Service Clinic Jan 03, 2015

    Without seeing the schematic, both the volume control and illumination, may be tied togther in the power supply. This is too old a unit to use a Rotary Encodre(new style volume cotrol), so that's not the issue. Your amplifiers are not bad; it's what's controlong them that is at issue. For more information, or to inquire about haing your Technics repaired, please visit my website at audioserviceclinic.com. You may contact me there.

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Anonymous

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Its the ic that controls the + and - voltage and there are capacitors that have leaked all the caps on that board need changing could be expensive and time consuming but its the age of it . if i was going to do that job £200 plus\

Posted on Dec 08, 2008

  • Audio Service Clinic Jan 03, 2015

    Not every issue in the world is a bad capacitor. These bad caps entered the marketplace in about 1999-2000. If they are not bad, you are wasting your time and money replacing them, just to turn it back on and have the same issue. Measure twice; replace once.

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jerrygadogbe

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My problem is the volume contorlb they use MN4030B and another MN which has blast on the circuit board.i will like to know number to replace it.This is my email [email protected] you can get me on face book jerrygadogbe.

Posted on Sep 07, 2011

  • Audio Service Clinic Jan 03, 2015

    This IC, and it's complement, MN4070B/S are logic ICs, and mostly, have nothing to do with a volume control control issue.

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www.djproaudio.com
www.repairny.com

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