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Chip Amps Amplifiers based on integrated circuits

Technics SU-CO4
Technics SU-CO4
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Old 16th March 2020, 10:38 AM   #1
EtVt is offline EtVt  France
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Default Technics SU-CO4

Hi !


I'm very new to technical stuff like this, but seeing the actual epidemic quarantine in my country I've got time to try to solve that kind of problem !


So I've got a Technics intergrated amplifier SU-C04 since 5 years. It has been working really well all this time. And yesterday, as I was preparing myself to spend a month home alone because of the virus, it just stopped working. When I push the start button, the light doesn't turn on and the sound neither.

I tried to open it and clean the dust inside but it doesn't change anything.

Any advice ?

Thank you very much


Etienne
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Old 16th March 2020, 03:03 PM   #2
adason is offline adason  United States
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did you looked at the fuse?
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Old 16th March 2020, 03:44 PM   #3
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-CO4
Check fuse - if blown, check for short in rectifier diodes
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I remember when amps were amps & speakers were nervous!
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Old 16th March 2020, 04:09 PM   #4
EtVt is offline EtVt  France
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Thanks for the advice. I'm sorry for my total inefficiency, but I'm not sure to know how to recognise the fuses and if they are blown.


Near the power cable, there are two tubes with written F1 T2A and F2 TIA, F1 is clear but F2 has a black smoke mark from inside. I guess it means F2 is a blown fuse right ?


How do I check for short in rectifier diodes ?


Thank you again

Last edited by EtVt; 16th March 2020 at 04:23 PM.
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Old 16th March 2020, 06:16 PM   #5
MAAC0 is offline MAAC0  Portugal
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DISCONNECT THE POWER CORD FIRST !!

Put a DMM in the ohm range between the fuse legs and measure.
If it's reading infinite it's blown.
This fuse protects the primary of the transformer.
The other is used for other country voltages according to the schematic.
Check if the voltage selector is correct.

Follow the wires from the transformer there schould be 4 diodes. You must measure each of them. In one direction DMM diode mode should read .6-.7V. Reversing legs should measure infinite.

Replace fuse and connect a 100W lamp in series with the mains and try to power it again. Check if it plays at low volume. If all is fine, remove the lamp and test again..
Lamp is there to protect the amp for further damage if there is a short.
As You aren't technically skilled ask a friend to help You.
If don't own at least a DMM stop and wait for better days.

Can't attach schematics but You can find them here:
Just Register. It's free.
Technics SU-C04 - Manual - Stereo Integrated Amplifier - HiFi Engine
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Old 16th March 2020, 06:34 PM   #6
EtVt is offline EtVt  France
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Ok thank you very much.


Last question : where can I purchase an other fuse ? What kind should I ask for ?


Thanks
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Old 16th March 2020, 09:57 PM   #7
sgrossklass is offline sgrossklass  Germany
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Do you have any stores selling electronic parts nearby? Otherwise look an Amazon or something, you'll probably be able to get a 100 pack or so. 250V 1A T (slow-blow).

These glass fuses basically come in two different sizes (European 5 x 20 mm or US 1/4" x 1-1/4" = 6.3 x 32 mm), so be sure to measure the length so you know which one you need.

The fuse itself isn't your biggest problem though. They almost always blow for a very good reason. (And if it's black, it clearly went rather violently.) In this case your most likely culprits would be either one of the 4700 F / 45 V power supply capacitors C601/602 or some of rectifier diodes D601-604.

To check one of the capacitors, first measure the voltage across its terminals. There may still be a few volts left, in which case the rustic method of using a screwdriver blade should discharge it. (If there is no voltage at all on just one of them, that one may be shorted.) Then use the multimeter in ohms to make sure it doesn't look like a dead short.
When picking replacement parts for these, the kind of and spacing of terminals as well as maximum possible outer diameter (and maybe height) are important. I would look at 6800 F 50 V or so, from either Japanese or Western manufacturers. Parts like this are best ordered from a reputable electronics distributor, not random Chinese eBay sellers.

Rectifier diodes can be tested with the diode test function. When they fail, they usually go dead short and measure 0.0 V instead of ~0.55-0.65 V. The originals appear to be 200V Vr, 1.7 A If types of no particular distinction, so maybe 1N5402 or 1N5404 would be suitable.

It is also possible that the output stage in one of the power amplifiers has had a major meltdown, in which case you would measure a short between C601 (+) and C602 (-). (On electrolytic caps, the stripe denotes the negative end.) In this case, testing would have to continue with output transistors Q507/509 and Q508/510.

I think at this point it would be wise to look up online courses on electronic parts, basic troubleshooting / use of a multimeter, electrical safety as well as learning to read a schematic if you can't already. HiFiEngine has service docs for this model.

One of the most useful tools for working on amplifiers is what's called a "bulb tester", which puts a lightbulb socket (to be equipped with a standard incandescent bulb of maybe 60 W in this case) in series with the amplifier under test. However, making one requires having at least a decent idea of electrical safety and having the tools available to make such a contraption in a safe way. If in doubt, ask an electrician or at least someone comfortable working with mains voltage.

BTW, why is this here in Chip Amps? Should be under Solid State. No chip amp in sight in this model, it's all discrete (save for one opamp in the phono stage).

Last edited by sgrossklass; 16th March 2020 at 10:01 PM.
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Old 17th March 2020, 02:36 PM   #8
adason is offline adason  United States
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Quote:
Originally Posted by EtVt View Post
Ok thank you very much.


Last question : where can I purchase an other fuse ? What kind should I ask for ?


Thanks
there is always a reason why fuse is blown
replace it with caution, if it blows again, you have another problem to worry about
but you may be lucky
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Old 18th March 2020, 12:17 AM   #9
Mark Tillotson is online now Mark Tillotson
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And read the fuse's rating from its end-cap, you may need a magnifying glass to do so. Its worth checking with the service manual too in case someone put the wrong fuse in last time (is it secondhand?)
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