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Old 16th November 2013, 09:24 AM   #1
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Default Ampli Technics SU-C03

When using the tuner or phono, few minutes after powering on the amp, there is a clack and the sound is cut. Then 10 or 15 seconds after the noise of a relay contact can be heard and sound comes back just. What could be the problem ?
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Old 16th November 2013, 09:40 AM   #2
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Possibly the relay hold transistor, or the associated circuitry. Try replacing the electrolytic capacitors in that area, I've had a very similar problem before and that fixed it.

EDIT: Here's the schematic. Doesn't look promising. This thing is full of ICs. Might be a tough repair. Not being too knowledgeable in the field, I'd try replacing C408 with a 33F/16V cap... I've read multiple times that 6,3V capacitors (as found right there) can be flaky.

Click the image to open in full size.
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Last edited by Welcome; 16th November 2013 at 09:46 AM.
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Old 16th November 2013, 10:06 AM   #3
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This might help you figure out what is going on.
Attached Files
File Type: pdf datasheet TA7317P.pdf (176.7 KB, 13 views)
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Old 16th November 2013, 10:56 AM   #4
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beyond the protection , functions and flaws of very low voltage electrolytics , you need to generally check for other leaking capacitors ( and if a few measure with a problem just replace them all )

Then you need to check things about soldering both in Power Ic but also in drive IC
Relays of protection click periodically in case of excessive Dc offset can be caused both from offset and soldering while the actual failure in the protection circuit it self is very low .

Finally check operating voltage of your area versus the amp ..If your voltage is 240 and amplifier is made for 220 these few volts more might cause some stress in the drive IC See if possible to adjust proper voltage from behind .

If there is no adjustment add a small heatsink to the drive IC ...it will help to long term stability ...

You also have a chance for a faulty drive IC if you need a new one proceed with caution there is plenty of fakes .

Kind regards
Sakis ...

Many IC and plenty of old transistors actually fail from mechanical reasons ...When you measure with a DVM all seems fine but under voltage the DUT fails ...Obviously if powered something goes wrong and most of the times this is mechanical where some heat expands the die and that looses contact from things that was supposed to be connected .Common failure in Vintage equipment
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 12th January 2014, 01:46 AM   #5
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I had similar problems with this amp.
The relay clicks in and out if there is issues, it doesn't mean the relay is faulty necessarily.

Try removing SUP17231 board (the one with the voltage amp stk-3062 on it)
there are a couple of plastic pins holding it in, the board just slides up out off the pins it sits in (amp is off!)

If the relay clicks in without the board in place, then you may well say the fault is on that board.
I replaced all the lytics all over, there arent that many, but some are damn awkward, I found a leaky on down by the relay control ic.
I think there was a bit of a design fault on the board mentioned in so much as the 2 zeners, and 2sa794 and 2sc1567 and the stk 3062 give off heat constantly, whether the amp is idle or not and so the electrolytics around there suffer. Also I have read numerous cases of the stk 3062 packing up probably due to overheating (google it) as sanyo reckoned it didnt need heatsinking. I replaced all the electrolytics, I replaced 2sa794 and 2sc1567 with bd139-16 and bd140-16, and further when problems continued at a later date I replaced the stk 3062 with a NOS from Germany. I also saw people modding heatsinks for the stk module so have modded one from an old graphics card to fit into that very awkward space. I am running it right now after just finishing the heatsink today and tested all voltages and waveform in the oscilloscope.

There are blank spaces on the board in question for other caps and resistors, I haven't checked but it may be that you can put in a stk 3062 and 3082 version II or III which are cheaper but apparently these need caps and resistors across certain pins (google again) but like I said, it may be that the board already has these spaces ready on the board, I haven't verified.

p.s I have the service manual if you need a copy. I will be posting it up on a couple of sites soon aswell. I already posted a schematic up to hifiengine.
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Old 12th January 2014, 12:45 PM   #6
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I just read OP point that it was happening on tuner and phone, no mention of tape and aux.
If the amp is fine on these 2 inputs, then ignore what I posted before.
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