Hello diyAudio,
my Technics SU-V40 has been working splendidly until a couple days ago when my left channel has gone very low suddenly, much to my chagrin. I've tried using both the phono-jack and crosstested with different speakers but the issues remains. The sound is not entirely gone but just very very faint.
Does anyone know how to go about fixing this, are there easy fixes to try? I'm very green with electronic repair and besides checking for burnt fuses I'm quite nonplussed as to what to do. I've tried searching for a service manual but no luck so far.
Any help is much appreciated!
my Technics SU-V40 has been working splendidly until a couple days ago when my left channel has gone very low suddenly, much to my chagrin. I've tried using both the phono-jack and crosstested with different speakers but the issues remains. The sound is not entirely gone but just very very faint.
Does anyone know how to go about fixing this, are there easy fixes to try? I'm very green with electronic repair and besides checking for burnt fuses I'm quite nonplussed as to what to do. I've tried searching for a service manual but no luck so far.
Any help is much appreciated!
Welcome to diyAudio 
A poor resolution diagram is available here (free to register)
Technics SU-V40 - Manual - Stereo Integrated Amplifier - HiFi Engine
It may not be good news on the amp front because this model seems to use a rather unique (read old and possibly unobtainable) monolithic output IC (IC402 on the diagram).
Obviously you need to do tests but that could well be favourite. An oscilloscope and signal generator (or test CD) would pin the problem down in a moment. Other possibilities... and it could be anything... include damaged print, perhaps around the volume control.
A poor resolution diagram is available here (free to register)
Technics SU-V40 - Manual - Stereo Integrated Amplifier - HiFi Engine
It may not be good news on the amp front because this model seems to use a rather unique (read old and possibly unobtainable) monolithic output IC (IC402 on the diagram).
Obviously you need to do tests but that could well be favourite. An oscilloscope and signal generator (or test CD) would pin the problem down in a moment. Other possibilities... and it could be anything... include damaged print, perhaps around the volume control.
You can find a free download for the SM here. Wait for a few seconds for the download button to become available.
TECHNICS SU-V40 Service Manual free download, schematics, eeprom, repair info for electronics
TECHNICS SU-V40 Service Manual free download, schematics, eeprom, repair info for electronics
(Fine here too!)
To the OP, you will find the SUV series amps are not typical class AB amps. These are derived and modified from copying Sandman's class S feedforward error correction scheme - which is somewhat like the principle behind Quad's 405,606, 306 models.
The point being that they are not easy designs to understand or troubleshoot and much is hidden in the custom bridge chip, IC402. As already mentioned, most models (and Technics had many similar types) use Matsushita's custom power semis and chips for the exacting operations so if these fail, your chances of repair become slim indeed.
To the OP, you will find the SUV series amps are not typical class AB amps. These are derived and modified from copying Sandman's class S feedforward error correction scheme - which is somewhat like the principle behind Quad's 405,606, 306 models.
The point being that they are not easy designs to understand or troubleshoot and much is hidden in the custom bridge chip, IC402. As already mentioned, most models (and Technics had many similar types) use Matsushita's custom power semis and chips for the exacting operations so if these fail, your chances of repair become slim indeed.
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Thanks for the tips. I think I'll try to open it up and remove any dirt/dust that might have accumulated.
Sad to hear that it's so hard to troubleshoot. Do you guys have any manuals or guides for a total beginniner in order to get to grips with the fundamentals of amplifier/eletronics repair? I realise that there might be a lot but I don't really know a good place to start.
Sad to hear that it's so hard to troubleshoot. Do you guys have any manuals or guides for a total beginniner in order to get to grips with the fundamentals of amplifier/eletronics repair? I realise that there might be a lot but I don't really know a good place to start.
This is expensive but gives a good introduction (probably the best book of its type)
https://www.amazon.co.uk/Art-Electronics-Paul-Horowitz/dp/0521370957
There is lots of stuff online... but no quick way to learn all this though.
https://www.amazon.co.uk/Art-Electronics-Paul-Horowitz/dp/0521370957
There is lots of stuff online... but no quick way to learn all this though.
Heh, heh! - an industrial control switch?
No, the selector switches on the SUV40 are those press switches on the central panel but the small switches at the top are most likely to give trouble. The lower bank of switches have a sliding action and don't usually show problems. My very similar SUV50 went silent when the tape monitor switch failed due to contaminated (blackened) silver plated contacts - both channels. - Difficult to find but easily fixed with cleaning solution and lots of pushing operation.
Not really I'm afraid. You need to understand circuit theory from the ground up for it all to start to make sense.
Understanding how feedback works would help and for that understanding how a simple opamp can be configured, and how the gain is set and so on would be useful.
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