Hello everyone,
I'm new to this forum and new to the audio electronics. I hope you guys can help me out.
I've recently picked up a used Technics SU-V470. Generally it is in good shape and sounds OK, however I noticed there is a slight difference in the R and L channel output. The right output sounds clearer and a bit louder than the left channel. If I turn the balance knob to 10 or 11 O'clock they sound balanced again. This applies for all inputs (CD/tuner/aux ect) and also for the headphone jack output.
Does somebody recognize this behaviour? Could there be something wrong in the pre-amp or power amp (faulty transistors i.e.)?
I have some background in electronics, however audio is completely new to me. Where can I start measuring? I already have the circuit schematics.
I hope you guys can help me out! 🙂
I'm new to this forum and new to the audio electronics. I hope you guys can help me out.
I've recently picked up a used Technics SU-V470. Generally it is in good shape and sounds OK, however I noticed there is a slight difference in the R and L channel output. The right output sounds clearer and a bit louder than the left channel. If I turn the balance knob to 10 or 11 O'clock they sound balanced again. This applies for all inputs (CD/tuner/aux ect) and also for the headphone jack output.
Does somebody recognize this behaviour? Could there be something wrong in the pre-amp or power amp (faulty transistors i.e.)?
I have some background in electronics, however audio is completely new to me. Where can I start measuring? I already have the circuit schematics.
I hope you guys can help me out! 🙂
could be the volume pot (or annother contact)...........
i would clean all contacts (rca jacks,fuses,pots,switches...........) with contact cleaner(spray). if it does not help,it could be a part failure.
i would clean all contacts (rca jacks,fuses,pots,switches...........) with contact cleaner(spray). if it does not help,it could be a part failure.
Tape monitor switch might be an issue since all signal pass from there . We often bypass them since hardly ever anymore one uses cassette players .
On this amplifier exist also a couple of thermistors located on the volume control pcb which the use of them is totally unknown to me . Even though i have repaired something over than 5-6000 amplifiers in my life i have never seen anything like that ever again
I will have to presume that thermistors sense temp inside the amplifier and decrease volume accordingly. you could remove them or swap them to see how it will work
In general these amplifiers suffer only from soldering issues down under and all over the board and cleaning issues ....Unit is quite young to have capacitor issues but still one feedback capacitor that has a failure might also present similar type of fault behavior .
Kind regards
Sakis
On this amplifier exist also a couple of thermistors located on the volume control pcb which the use of them is totally unknown to me . Even though i have repaired something over than 5-6000 amplifiers in my life i have never seen anything like that ever again
I will have to presume that thermistors sense temp inside the amplifier and decrease volume accordingly. you could remove them or swap them to see how it will work
In general these amplifiers suffer only from soldering issues down under and all over the board and cleaning issues ....Unit is quite young to have capacitor issues but still one feedback capacitor that has a failure might also present similar type of fault behavior .
Kind regards
Sakis
Does sound like an issue with the volume control to me rather than a circuitry issue. Sometimes they can go like that and not crackle.
Given that the problem position seems to be where it would have been likely to have been nudged up and down a bit then it becomes more likely too.
If it was something with the circuitry it wold happen with similar level not similar volume position.
Given that the problem position seems to be where it would have been likely to have been nudged up and down a bit then it becomes more likely too.
If it was something with the circuitry it wold happen with similar level not similar volume position.
Just seen sakis' post. He has some good suggestions. I've never encountered thermistors in a volume circuit before so it would be a good starting point.
That makes sense! I will take them out and replace them with equivalent regular resistors.
I assume these are the thermistors on the volume pcb?
Ok I measured the resistance from each thermistor and they seem to be giving both 50kohm at room temperature. So no problem there, however I'm going to replace them anyway.
Next I reheated all solderjoints on the volume pcb. After I had done this, I noticed the volume pot didn't turn as smooth as before. I can hear the pot actually grinding when I turn it. Obviously some kind of lubrication has vaporized during reheating of the solderjoints, or dirt came loose inside the pot..
So I guess now I'll have to spray it in anyway. I will use Tuner 600, however this will not lubricate the pot I think? Do I need it to spray with some other solution?
Next I reheated all solderjoints on the volume pcb. After I had done this, I noticed the volume pot didn't turn as smooth as before. I can hear the pot actually grinding when I turn it. Obviously some kind of lubrication has vaporized during reheating of the solderjoints, or dirt came loose inside the pot..
So I guess now I'll have to spray it in anyway. I will use Tuner 600, however this will not lubricate the pot I think? Do I need it to spray with some other solution?
Success!
I replaced the thermistors with regular resistors and sprayed in the volume pot with Tuner 600. The amp is fully in balance again and sounds perfectly!
Thanks for helping me out!
I replaced the thermistors with regular resistors and sprayed in the volume pot with Tuner 600. The amp is fully in balance again and sounds perfectly!
Thanks for helping me out!
I have a new problem now with this amp.
Recently I picked up a pair of Mission 760i's, replacing my JBL TLX-121.
Since I've connected these 6ohm speakers, the right channel cuts off regularly. It still gives me output, however at much lower volume and with crackling noise.
If I rapidly turn the volume up and back down, the right channel starts playing again for a while.
At higher volumes, the right channel doesn't cut off. Only at lower volumes.
I already tried to clean the volume potentiometer again, but it doesn't help.
When this problem occurs, tapping the case or volume knob doesn't help, so no loose connections/solderjoints..
Does this sound like a transistor problem?
Recently I picked up a pair of Mission 760i's, replacing my JBL TLX-121.
Since I've connected these 6ohm speakers, the right channel cuts off regularly. It still gives me output, however at much lower volume and with crackling noise.
If I rapidly turn the volume up and back down, the right channel starts playing again for a while.
At higher volumes, the right channel doesn't cut off. Only at lower volumes.
I already tried to clean the volume potentiometer again, but it doesn't help.
When this problem occurs, tapping the case or volume knob doesn't help, so no loose connections/solderjoints..
Does this sound like a transistor problem?
It could be a speaker relay problem, the relay having tarnished contacts . The symptom of it being OK at high volume is a classic. Just run some clean paper soaked in ISO or meths or WD40 through the contacts to clean them.
Thanks Mooly, it worked!
Didn't seem to be a lot of work, so I cleaned them today.
Contacts were indeed a bit dirty, now my amp sounds great again!
Didn't seem to be a lot of work, so I cleaned them today.
Contacts were indeed a bit dirty, now my amp sounds great again!
Hi Guys , i also have the same amp . problem i have is no sound at all , all lights come on , glass internal fuse is ok , no head phone volume either , even when on direct output , tried all source inputs to no avail .
I got the amp for £30 , but cant afford a £70 repair . I have a soldering iron familiar friend . Where should i start . thermistors look interesting .
many thanks in advance . Tim🙂
I got the amp for £30 , but cant afford a £70 repair . I have a soldering iron familiar friend . Where should i start . thermistors look interesting .
many thanks in advance . Tim🙂
I have the same problem with the SU V 7 and had a look at the service manual.
In the Volume section i dont see any TH's: TECHNICS SU-V7 Service Manual (Page 5 of 8)
But here are 2 of them: TECHNICS SU-V7 Service Manual (Page 6 of 8)
TH304 & TH302
Could it be the source of the problem on the SU V7 as well?
In the Volume section i dont see any TH's: TECHNICS SU-V7 Service Manual (Page 5 of 8)
But here are 2 of them: TECHNICS SU-V7 Service Manual (Page 6 of 8)
TH304 & TH302
Could it be the source of the problem on the SU V7 as well?
I would doubt the thermistors are faulty... and both of them... its just not going to happen tbh.
Hello Mooley, thank you for your Comments i just seem them (hidden on page2)
We have cleaned the relays for the speaker selector and still measure the L/R unblance on the oscilloscope. Its the same deviation in low and high volume.
But the it drifts a bit more off when applying higer frequencies. Could that indicate something useful?
We have cleaned the relays for the speaker selector and still measure the L/R unblance on the oscilloscope. Its the same deviation in low and high volume.
But the it drifts a bit more off when applying higer frequencies. Could that indicate something useful?
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