diyAudio - Nikoo A-300D, recapping dilemma...

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Nikoo A-300D, recapping dilemma...

Hello All,
I have this little Nikko Amp(A-300D) which I am in love with.. It’s my bedroom system and I acquired it from a gentleman here in Singapore few years ago… It still works flawlessly... Today I thought may be I should recap it, and use with a pair of Altec Lansing Corona 893B.

So I opened it up again to take a closer look… Lo and behold... It seemed like someone has already changed few caps… Or at least I can see wires with soldering iron burn-marks… Seems like someone as dexterous as me was at work…

Things like power supply filter caps seem to have been replaced.
Currently it has Elna 2200µF/35V Electrolytic caps… And I can also see Korean brand Samwha electrolytic caps as well… I dont know how good they are but that looks like a replacement job too…

The main arguments for the recapping are; there are less than 24 caps on the board in total and the PCB is a simple layout single layered design with abundant use of wire jumpers to complete the routes. All the electrolytic caps are nicely indicated with polarity/orientation on the PCB(with the symbol as well as ‘+’ marks)… And All the values can be read.

But considering my dexterity when it comes to soldering, I am still a little hesitant to embark upon a “change’em all” mission… Only if it is worth the risk :) I would also like to go audio-PP way for Caps on the signal line… But I don’t have a schematic…

So is there any easier way to identify the coupling caps, than to manually track the lines? Better if someone has the schematic (which I am really not very hopeful of)

Quote:

Originally Posted by Ronj (Post 2700825)

The main arguments for the recapping are; there are less than 24 caps on the board in total and the PCB is a simple layout single layered design with abundant use of wire jumpers to complete the routes. All the electrolytic caps are nicely indicated with polarity/orientation on the PCB(with the symbol as well as ‘+’ marks)… And All the values can be read.

So, to understand you correctly: The main reason for fidling with the amp is: "because it's possible".
Now, I don't see anything wrong with that, but only if you like the smell of resin. The best technical result I can think of is that it still works as good as it does now after you'r finished (on offence)

Quote:

Originally Posted by blistard (Post 2700834)

Well.. The main reason I thought was, this being a 1970s amp, theoretically the electrolytic caps on the amp should be either at their end of life or drifted considerably from their specs...20years is what people say electrolytic caps really last… I am not even sure how this amp is actually supposed to sound in fact... Of course being a vintage Nikko, it may not be as detailed or fast like some of my newer amps ( Pioneer A400, Marantz PM6003 etc). But I suspect the desired sound from the amp’s designer would have been tighter and more detailed presentation. And I would like to use it for years to come…

(on offence = no offence)
Ok, now I understand. I feel the problems with aging capacitors and the benefits of changing them are much exaggerated, but this piece might give you some infomation ELNA AMERICA, INC.
To find the coupling-caps, without a schematic, I think tracking the traces is the only option.

I went ahead and ordered all caps.. All 32(yeah I missed counting few earlier) of them! :) And element14 delivered them to me this afternoon! Yet to open the package though...

An unusual find... Spend 20mts earlier today and I found that there is a 3300µF/50V cap as well... I tried to trace the tracks to see where it is powering, it seems to be supplying a Single power supply which is marked as B+ and those 1N4007 type diodes you see in the below picture( see in half-bridge configuration) seems to be the rectifier section for this cap...

Having said that I didn't get time to find the rectifier section for the dual rail supply with twin 2200µF/35 caps. the bigger diodes in the picture, I am not sure are part of oa full wave bridge setup, but then i couldnt find the remaining two diodes... neither I could continuity trace them to any of the 2200µF caps... May be I need more time those 20mts were not good enough... thats what happens when there is no schematic :)

You might have to take caps in higher voltage rateings to get the same pin pitch as modern caps which tend to be much smaller for a comparable capacitance.

Today I started changing the caps and I am half-way through... I did find a few dry solder joints also along the way....

Then I saw that two diodes are kind of glued to the heatsink per channel... and one of them got unstuck... I don't have any idea what kind of glue it is.. I have never seen something like this before... Can any one here please help me out what compound is used to glue diodes to heat-sink? It looks like rust colored now, as there is some rust also on the heat-sink where it was stuck... below are the pictures... please look at the red oval's i marked to identify them... Any suggestion on what to use to stuck them back on to heat-sink is really really appreciated!