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need help with amp

i know the title does not sa much but thanks for looking anyway.

so the story is that a few months back i helped a friend to trow some stuff away, as payment i got a Nikko na 590 amplifier and a pair of speakers. all in different stages of distress.

when i checked the amp i noticed that the fuse had gone, i replaced it with a new one but it blew out faster than i could say ''oh snap''
after looking around the web and the amp i checked the ac power transformer and found out it had shorted out, i had a friend check on it as he has some knowlege about electronics and he agreed the it had shorted out.

so i need a new one, this might be a stretch but does anybody know where to buy a ac power transformer?

i have no knowlege about this sort of thing so if anybody could help me out it would be much appreciated.

Re: need help with amp

so its been a few weeks since i posted anything now and i said i would post when the transistors arrived,
now they arrived a few days ago and i have installed them in the amp.

lo and behold the amp now works, altho it does have a slight hum to it.
so just to recap these new transistors are the same models as the ones in the amp. when i installed them i added some noctua thermal paste to them between the transistor and the heatsink.

regarding the hum coming from the amp thats something i would want to look into at a later date,
the hum depends on where and what speakers i use as when i tested it in my ''workshop'' withe my terible test speakers( some old paper cone philips speakers from an all in one system) the hum is much worse than if i use my main living room speakers (marantz hd 660) the hum is much less severe.

tho as my freind pointed out the hum might be made worse by the lights in my workshop.

thanks for all the replyes in this tread and also for all the help

Re: need help with amp

The humming is not a good sign; the main filter capacitors may be bad, or it could be other capacitors or a combination of several. I doubt if your lighting is the problem. Also, there still could be bad parts in the amplifier. Is the hum equal on both channels?

Re: need help with amp

yes it is in both channels, i have plans of replacing several components in the amp such as the capacitors in the future as an exercise but for the moment i dont have the money or the tools neccecary.

Re: need help with amp

About the only place to find a vintage part is from a junker unit, maybe on eBay. How did you determine the transformer is bad? They rarely go bad; more likely to have output transistors or modules short.

Re: need help with amp

i will try to explane this to the best of my abilities but i used a voltmeter and checked the connection points around the fuse and the ones going in and out of the transformer.

i have to admit it is a while since i did this and my memory is worse than that of a goldfish but the wire that goes from the fuse and in to the transformer sendt the power around and back the other power input.

that is that you have + and -
and - goes to the fuse
+ goes in to the transformer
i put the voltmeter on the setting that emits audio when there is a connection between + and -
put one end on the - side after the fuse.
there is only a connection when it put the other one on + going in
there is no connection after the transformer going in to the rest og the amp

when it comes to voltmeters i only use them to check connection as i dont know how to read the numbers.
i don't know if this is a good explanation but feel free to call me a dummy

Re: need help with amp | transformer

It is extremely unlikely the transformer is shorted. If it had overheated to the point of melted insulation subsequently bridging turns in the windings, the smell of burnt insulation materials would be readily apparent. Shorted windings without overheating or blunt force torque (being dropped, hit, etc.) are very uncommon. Since you have limited technical proficiency and this phase of diagnosis involves high voltage, it is advised you seek out a technician who specializes in vintage gear. The two main faults associated with immediate opening of line fuse are shorted output transistors and shorted diodes in the bridge rectifier. Either of these situations is readily fixed by someone familiar with the components and circuitry. Nikko made some nice gear and this model is a decent design: fully complementary outputs, differential input stage to power amp and dedicated phono preamp. It is worth saving and will make a nice system base for living room or office setup. Don't risk causing more damage, get someone who's technically inclined to investigate the failure. The money will be well spent. If it costs $ 250 to fully restore the '590, it will still be leaps and bounds superior to most any new equipment which sells for twice as much.

Re: need help with amp | transformer

thanks for you'r reply,
whilst you do make a good point about it being extremely unlikely that the transformer shorted out, the friend that i got it from got it from some of his friends and thats the kind of crowd where blowing speakers and clipping amps is like just another day of the week. i think you know what kind of people im talking about so in short
yes its highly unlikely but still a possibility.

as for your other point about sending it to a technician thats out of the question. living in Norway these people are few and far between and most of them only work on old Tandberg or Radionette stuff.
therefore there is a massive headache just finding one to do it, then sending the unit and then i bet you it will cost more than 250$

besides i got like 3 amps beside this that are just as good if not beter might i say so spending money at it when i might not even have use for it might be a bit of a waste from my side.

but i do plan on trying to get it fixed myself, just for fun and learning

Re: need help with amp

I don't know what kind of meter you have, but if it is a DMM (digital meter) then the only function I know of that has audio is the diode test. This setting is not good for testing transformers. You would need to use the ohmmeter (resistance Rx1) setting; for a power transformer primary you should get a reading of maybe 5 to 8 ohms. There should not be any readings from the primary to the secondary windings.
One test you could do is unsolder the two white wires coming from the transformer, then see if the fuse still blows. Make sure the wires don't touch anything. If the fuse does not blow, then there is a short somewhere after the transformer, most likely the amplifier or possibly the power supply filter capacitors or rectifiers.

Re: need help with amp

thanks for the reply

i do use a digital meter, its a cheap one but it works as i got recommended it from an electrician i once knew.

i have done the test that you discribbet here about desoldering the white wires and it did just as you said.
the fuse did not blow, so thanks to you i have found out that its not the transformer but something else on the amp.

this does need some digging in to, so far all that i have done is to do a visual inspection and i see no blown caps or any other damaged part but then i see that there are 3 caps. 2 big ones an one small(how specific i know) that have some sort of harden liquid underneath them.
might be glue or flux or acid, i have to look more into that.

i also want to do an inspection underneath the boards just to see if there is anything that could lead me to the culprit there.
im also going to learn how to use the meter and measure the different point on the boards.

anyways thanks for you'r help (so far)

Re: need help with amp

It is most likely that some or all of the output transistors are shorted (2SD586 and 2SB616). If these are bad then the driver transistors may also be bad.

Re: need help with amp

i have looked over the amp but i cant find those parts you are referring to.
are you looking on the schematics for model 1 or model 2?
i have the model 1

Re: need help with amp

Only the model II is listed here on hifiengine. You will need to test all the output transistors. If even one is shorted then you must test other parts around it in the circuit, like diodes, resistors and other transistors.

Re: need help with amp

ok so i fount the transistors, the where underneath the heatsink so i had to dismantle the front on bottom to access them.
so i have already subjected them to my amateur diode test, and their is signal is showing up all kids of places.

so if you could teach me how to find out if the transistors are shorted, how do i go about measuring that?
i have a digital meter but i do not know how to read of the various thing's on it, i only know the diode test.

Re: need help with amp

1st thing to do is discharge the filter capacitors (the big ones--should be 6800uf); just put a jumper wire across the terminals when the amp is unplugged.
I assume you have a digital meter with diode test; most will read about 3 volts with open circuit. Find the output transistors; the pin on the left of each one is the base. Place one test probe on the base and the other on the center pin which is the collector, then the outer pin which is the emitter. Depending on whether this is an NPN or PNP transistor you should read open on both pins, or conducting on both pins. Conducting will read about .6 volt. If you get a 0 volt reading it is shorted. If this seems too involved watch some Youtube videos on testing transistors. Note; if any transistors are shorted they should be replaced as pairs because high current went through all the transistors.

Re: need help with amp

thanks for you'r help. i watched some videos on youtube and they are shorted.
i did find some new ones on ebay that im going to order, but it will take a few weeks for them to arrive.

once they arrive i will post an update

Re: need help with amp

Just a word of caution. There are a lot of counterfeit transistors out there, especially on ebay and especially for transistors that are no longer in production. They may function correctly at first, but the counterfeit ones are undersized and won't be able to run at full current rating without failing. My go to source for Japanese transistors is BD Enterprises. www.bdent.com. If the originals are not available, the website will suggest alternatives.


Re: need help with amp

What are the numbers on the transistors ? Are they the same as what Johnysan stated or different?

Re: need help with amp

they are the same

one nec b616 and one d586