DIY -Change capacitors - Nikko na 550

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Stereo Amplifier Nikko na 550


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Purpose of the operation: Complete renewal of electrochemical capacitors.
Adjusting the BIAS output transistors (quiescent).
Cleaning the knobs and different contacts.
Note: For marking of components on the PCB, they can be wrong. Do not overheat welding because the tracks tend to peel off.

1 / Taking the measure of restoration before quiescent current.
2 / A photograph of the card.
3 / Use a marker to identify the polarity of the capacitors with a marker.
4 / Change capacitors one by one to avoid an error.
5 / Treat welds and pay close attention to the polarities.
6 / Before reconnection, do a check of the cards.

Adjusting the BIAS after changing all capacitors..

Setting the quiescent currents (powers of the amplifier circuits).
Do not apply signal to the input of the amplifier, volume 0.
Output terminals of senior speakers: nothing connected.
Use only a multimeter, and know the precautions and safety measures face a unit. The voltages in the device approaching 250 volts!

Left Channel:

Adjust the variable resistor(R729) check the voltage across points (TP 35 et TP 36), and set to 9 mV quiescent current.

Right Channel:

Adjust the variable resistor(R730) check the voltage across points (TP 37 et TP 38), and set to 9 mV quiescent current.


A transformed amplifier, much more musical, a much more detailed.
A very well built device, to discover the plastic began to be used.

 transistors nikko

Bias adjustment of Right

Bias adjustment of Left

touch points

touch points on pcb

Schematic 1 of Nikko na 550

Schematic 2 of Nikko na 550

Schematic 3 of Nikko na 550

Schematic 4 of Nikko na 550

Nikko na 550