NIKKO ALPHA II setzt aus

Hi,

Your amplifier is rather old and by now it is time to think about a re-cap.

All electrolytic capacitos should be replaced, except perhaps the main capacitors (4 x 10.000uF/63V) in the power-supply even if I think it would be wise also to replace them.

Now most likely what happens is that the protection-circuit itself is defective. Nikko did a couple of crazy things in this circuit possibly to save on money. Instead of using a bi-polar electrolytic capacitor they just used 2 ordinary polarized cap's minus-to-minus. Allthough this in theory makes a bi-polar capacitor in praxis it's the cheap-and-dirty variant.

Replace ALL electrolytic cap's in the protection circuit. They are:
C841 & C842 (The cap's described above) -> 220uF/16V
C844 -> 3,3uF/35V
C843 -> 220uF/16V
C840 -> 0,47uF/50V
C719L & C719R -> 0,47uF/50V
That should cure any instability in the protection-circuit.

Now consider the electrolytic cap's in the output-amplifier are of equal age. They will also soon cause all kinds of instability problems like self-oscillation and destruction of the output transistors when they finally deteriorate enough. Replace them now and enjoy many more years of pleasure from the Alpha-II.

These cap's are:
C701L & C701R -> 100uF/16V
C703L & C703R -> 220uF/80V !!
C707L & C707R -> 10uF/25V
C706L & C706R -> 470uF/16V

In the power-supply are 8 cap's that I would also replace:
C801~C808 -> 220uF/10V

With all capacitors use the same or higher voltage rating. Use 105-Degree Celsius capacitors, they last longer than 85-Degree variants in my opinion.

The above 're-cap' will be VERY inexpensive compaired with a burned-out amplifier caused by defective capacitors.

If you can do it yourself..??
Well, do you know how to use a soldering iron for starters?

mfg,

/tri-comp