Nikko Power Amplifier Alpha II Stuck On Protect - diyAudio
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Old 28th January 2010, 02:39 AM   #1
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Default Nikko Power Amplifier Alpha II Stuck On Protect

I can get the amp to play if i manually move the protect relay over. but i understand its the e-caps that need to be replaced on the pcb? if so how do i test them

thanks guys

Jack
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Old 28th January 2010, 04:22 PM   #2
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caps need to be replaced one way or another ...there is no point tetsing them ...simply replace them

Nikko amps after some years fail on the psu caps also so you need to take a look at that also

Some of the designs have also two sets of voltage one for the outpout and one for the front end there you need to take a look also the rails are fused with diferent fuses so you need to check everything before proceeding

points to take care of is the electrolytics arround the protection circuits and also the vbe multipliers attached in heatsink cused trouble in a couple of times

also a schematic will be a good place to start ( which i am sorry to say that i am looking for also ) eventhough all nikko amps that come in to my hands have been repaired allready but having it is a good thing to

some extra help you will get from here mostly regarding the procedure
vintage amplifier repair/upgrade manual
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 30th January 2010, 11:31 AM   #3
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here is some more news

a few minutes ago a NIKKO AII together with paired preamplifier come in to the shop for repair ... afew damages here and there and will also need recaping

we both have no schematic but that is ok for me i can repair it with or without it

so if you need my help your more than welcome to post

regards sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 30th January 2010, 04:30 PM   #4
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for fun ....

this particular Nikko belongs to a costumer that realy wants to play with the amp ... so this one we will strip down and replace almost everything ...given the oportunity i will try to upgrade a few things ( a good point is to remove all ceramics beyond all the elctro's )

the amp has blown one channel ( fair enough since one of the rails was almost AC since about half a glass of juice was missing from the cap bank )

will remove all capacitors ( all means all ) and present my work in details in a few days

regards sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 31st January 2010, 10:12 AM   #5
Bigred is offline Bigred  Canada
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Havin one of these can make life easier
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File Type: jpg Nikko Alpha II Amplifier(sm).jpg (138.6 KB, 237 views)
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Old 31st January 2010, 10:41 AM   #6
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amplifier is allready repaired and upgraded ...just finished late last night .... after all it was very simple ...
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 31st January 2010, 11:00 AM   #7
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what i found inside

damages :
----both output tranistors where gone in the wind from one channels
---- took with them one of the drivers + one of the predrivers
---- from the four caps ( bank ) i found one with extensve juice leak
---- all other small caps where also gone
---- the lamps of the wonderfull VU meters also gone ...

procedure

//since outpouts where gone and driver also i thought about replacing all outs with something more modern and more rowbust if possible MJ15024-25 was a good choise since it was available in excelent quality ( i do have a wonderfull stock from many good quality tranistors ) replaced including all the mechanical

// pre driver and driver pnp 2SB536 ( 40 mhz !!! ) was impossible to find and if found the quality is going to be questionable ...so decided to replace all drivers with MJE 15032-33 that sounded like a wise choise but also proceeding like that saved me the trouble to find or replace predrivers since pre driverss and drivers was the same tranistor so i was despert for one gone predriver

// all electrolytics ahere replaced both banks and small here and there some of them beefed up and all of them at least double the voltage ... then again banks where rated at 63 volt which i found kinda low takeing also in mind that amp now works at 240 volt ....so i put inside 10000 mfd /100v ,added mundorf 100 nf 63 on the top of every cap

// replaced all ceramics with better quality ( styroflex) input filter is silver mica now and after extensive tests 100 pf ceramics at drivers miller caps where replaced with 68 pf styroflex, bypassed the input cap 220nf ,

// add multiturn trimers for the idle , biassed at 120 ma , offset was 16 mv for the left channel and 20 for the right

// replaced all lammps with 12 volt 2.5 W ( no daylight filter though available )



after that i have never seen eveything so square at 100 khz !!!!!!

done with scope readings didnt have time to listen to which i ma going to with in the next days

regards sakis
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 8th February 2010, 07:24 AM   #8
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as about the schematic i also have it and i will be more than happy to share it .... feel free to e mail me

its kinda large to post in the forum

is this ok with you big red ???
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 27th March 2010, 03:23 PM   #9
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Default nikko alpha II : missing protection card

Hello,
I purchased a Nikko Alpha II amplifier which work great, but has a missing protector circuit card.
I planned built one with the help of the service manual provided by Sakis (thanks again, mate ).
But after having searched for components, I had to admit that I am not good enough for that : I am able to assemble a kit and solder, but not to find a replacement for the discontinuted relay or diode
So, here is my question : is it worth building a new protector circuit, or is it cool to live without it ? What is the risk, as far as I don't switch the speaker on to soon after power up ?
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Old 28th March 2010, 11:09 AM   #10
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Some on another forum told me about Velleman K4700 card. Do you guys think that it will be good for the Alpha II ?
Reading the schematics I do understand that connexions are quite different between Nikko's original card and the Velleman's one (4 cables coming from amp cards connected to Nikko protector card, but only two connectors on the Velleman). Is that an issue ?

Regards,
Luc
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