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Repair and disassembly information for amplifiers in home audio systems.

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Amplifier with no sound

Hi!

I have a Dual CV 3530 220V 50Hz amplifier with STK chip attached to a giant heat sink in it. I'am in Europe. It doesn't make any sound when connected to the speakers. I tried to connect headphones but they blow up immediately.

I tested things like :

-solder reflow

-cleaning the main volume potentiometer

No components seem to be blown, the main fuse is not melted and I don't know what to do next. I don't know if the speakers are blown, but they seem a bit sticky.

PS: The only thing I found online is a guy who sold one once in Russia, so no schematic…

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2 solutions

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The first thing to look for is capacitors that have “domed” or are bulging at the top.

A brown substance may, in extreme cases, leak out from them.

Replace any of these with capacitor with same specifications which are easily read on the side of its case.

I fixed a NAD C352 amplifier by replacing the main power boards 2 large capacitors which had “domed”.

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Hi and thank you for your answer!

They are two huge 6800 microfarad capacitors. Their top are black and domed but I can’t tell if it’s a default or not.

They two have some solid stuff at the bottom but it seem to be glue. Anyway, I think you are right and I will try to replace them.

par

@lazyfox

If they are domed then they are no good. They should have a flat surface on the top.

The voltage and temperature specifications should also be written on the capacitor.

If you can't find a replacement capacitor with the same voltage specifications get one where the voltage rating is higher as this won't affect the capacitor's function but definitely not lower than the specified voltage rating.

The important specification is the capacitance. It must be the same as the circuit was designed for that value. The voltage rating matters as it has to work at what the voltage of the circuit is where it is connected. If its' rating was lower it would be destroyed

if the solid stuff at the bottom smells "fishy" it will be the electrolyte from the capacitor, otherwise as you say it may just be glue to help take some of the strain off the capacitor's leads holding it to the circuit board

par

Thank for all of your explication, I just have a last question: the capacitors are rated 50wv, does it mean 50v?

par

Hi @lazyfox

Yes

50wv means that it is rated to work with voltages only up to 50 Volts (50V), not more than that.

wv = Working Voltage

Since it has that rating do not use a capacitor with a voltage rating <50wv but it is OK to use one with a rating >50wv if you can't find one that has a rating of 50wv.

You also have to keep the dimensions of the capacitor and the lead spacing in mind as it has to physically fit onto the board and in the case and also connect to the circuit board if it is the through hole type. Perhaps measure the original ones to get an idea i.e. height, diameter and lead spacing

Here's an example that shows all the specifications i.e. capacitance, voltage, tolerance, type -radial, dimensions and lead spacing (distance between the capacitor leads)

Cheers

par

@aactech

https://www.mouser.fr/ProductDetail/Nich...

Those have everything good (diameter, ratting ...)

par

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STK chip attached to a giant heat sink may be out. You might consider replacing it.

CAUTION: If you decide to take this on yourself unplug the unit from the wall and discharge the capacitors. Beware of LETHAL HIGH VOLTAGES. The can kill you.

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I let it unplugged 2 week so I think it's ok but I will discharge the capacitors anyway. I just need to find a replacement for the STK chip.

par

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Edouard Sourice sera éternellement reconnaissant.
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