The power module contains high volatege parts　300V DC, high enough for your heart to arrest.  Please wear high volatage protection globe before touching.  And discharge DC high voltage with 10w 100 ohm resistor everytime you are done.

unscrew and open the cover of your power module.  The power module consists of two parts, one is AC to DC conversion board and the other is DC to DC converter.

The right board is AC to DC,  and the left one is DC to DC.

The building blocks are AC 100 to DC 140 taking ripples.  Check this board first.  

From this board, there two connectors, one is pure DC 140V and the other is sensing wire?

With AC connected,  check DC 140V.  

Next  there is a part signed as "high volage"  with white mark.  there two FET which are supposed to drive this DC140V 

to  transformer.  With Oscillo,  check AC input and AC out are measured source of FET or the transformer.

inside of  white line  are two FET, with high voltage, you have to use oscillo scope to check AC.  If you observe AC, skip this section.

my case was  there was no AC before transformer. so I check sensitive area, noted on the board.  There were two micro

transistors, one of which was not functional, so I replaced it with 120V NPN.  

Discharge DC 140V with resistor 100 ohm 10 W.

And you have to locate flyback switching IC, TOP266VG.

The above black one is TOP266VG. It is very hard to remove.  you can see I almost burnt the board.(above)

If there is no AC across FET or the transformer, then the flyback IC is broken.  which is located in the area marked as

"sensitive".  The IC resposible for switching converter is TOP266VG.  micro trasisitors and photocoupler might be burnt.

so check those parts using your tester.

My case was I had DC 140V, the FET was functional. but micro transistor with input voltage 110V and  photo coupler

and TOP266 seemed unfunctional.

I replaced it.

I changed micro transistor above  inside sensitive area, 110v operating.

taking top266vg left and new one on right

Let me check if this produces AC on FET.    AC out came on screen.

Scope probe should be on FET output above.

I had broken photecoupler, so a replaced.

I got DC 12V out.

What I found was,  when TOP266VG was replaced,  DC input voltage reached 300V, instead of 140V when no AC on FET was produced.

ANYWAY,  it is very dangerous.  so use high voltage protection globe.  discharge everytime

Good luck.

I thought  it has been repaired, but 5V power line indicated 12V.  which means it is not yet fixed.

The voltage layout on the connector shown above is written on the right note.

number 1, 7, 10 should be 5V, but they indicated 12V.   so I have to find DC to DC converter problem.

This should indicate 5V instead of 12V.  Yellow lead is supposed to be 5V. 

 I started to take all the capacitors coupled to DC outputs.

to be continued.

WHOOOOOPS

correction.  I found a new document for Z620 PSU pinouts, according to which, the PSU does not have 

5V or 3.3V.  read the following:

 continued

so my repair seems complete.   I was too short  minded that I took all the capacitors out so I have to put them back.

good luck. 

I am now changing capacitors.　　I could not get small ones so I had to use old ones.  I changed capacitors like  this

black capacitors are the ones that I changed.

I put everything together to check output.  fan was running, green LED was on.  #18 pin indicated 11.85V

I have another PSU and checked the outputs on each pin.  # 1 7 10 were 12V.  #18 was 11.85V.

Finally, I tested the PSU on PC.

Running without any trouble.

I guess it is fixed.

I label parts I replaced.

TOP266VG     Capacitors      photocoupler        chip transistor(NPN 120V)

Good luck

まずは中古で手に入れたのを鳴らしてみたのですが、　案の定　ns10 と同じように

ウーファーのエッジが硬化して　低音がならない。

アテニュエーターも　ガリガリ音がします。　　ばらしましょう。

まずは、スピーカーを外します。ハンダなので外さないとならなくて。　次にアテニュエーターは

つまみはペンチで引っ張りました。　奥のねじを外すと

奥にネットワークがあり　爪をピンセットで工夫して外すと

全部出てきます。　アテニュエーターはもうばらしました。

基盤を見ると　

コンデンサーは　３５micro 15micro  大きいのは１６０V　2.5 micro 　3.5micro Farad でした。

これらは　まだ使えそうですが、　交換します。　

次に　アテニュエーターの背面の金属をドライバーでこじ開けると

コイルの面は問題なし。　おそらくセンターの部分にグリスがこびりついていると推測します。

ばらしたいのですが、　後ろをかしめてあるためこれ以上はばれません。　工夫して何とかガリを取ります。

ガリが取れたかを検証するために　スピーカーをつないで音をならしてまあまあ取れてました

ウーファーのエッジが固いので　ブレーキオイルをほんの少し　筆で塗って　チリ紙で拭いて

一晩おくと　ふにゃふにゃになります　筆で押してふにゃふにゃを確認。　オイルはウレタンも溶かすので注意してください

さて　パーツが届いたので　組み込みます

3.5 2.5 micro farad は組み合わせで作ります。

一部外して　取付して

箱の中に戻して　スピーカーを戻します

この状態で　アテニュエーターの作動するか確認して　グラスも戻して

出来上がり

このスピーカー　すごくいいです。　低音から　高い音までよくなります。

音量を大きくしなくても　すごくいいです。

ベストセラーのＮＳ１０も　オーバーホールしたけど　こちらのほうが

数段　いい音です。　好みもあるけど　

このウーファー、　ブレーキオイルでウレタンを柔らかくしたら　すごくよくなります。

感動。。。。。。

さすが　ヤマハ。　　　ＮＳ１０は卒業します。

Ｎｓ１００Ｍ＞＞＞＞＞　ＮＳ１０　ですね