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Old 22nd October 2014, 12:41 AM   #1
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Question Nikko TRM-750 recapping project

Hello people,

I'm about to recap an old Nikko TRM-750 amplifier. It exhibits a lot of symptoms in the sound that could point to the capacitors being bad. Two of them are visually leaking and some look like their tops have been extruding.

I'm a total beginner at this stuff, so I'm essentially just posting my game-plan here in the hope that someone is kind enough to tell me if anything is completely wrong.

The goal is not to restore its original "vintage-sound" but to have an amplifier that sounds as good as possible by modern standards - within a fair budget of course.

I have cross-checked the service manual with the electrolytes actually inside the amplifier and come up with the following list:

Code:
Qty	uF	Volt	Remarks		Parts No.	Replacement

2	0.47	50	Blue (LC) 	211505L		Nichicon FG
1	0.47	50	Grey		211505Q		Nichicon FG
3	1	50	Grey		211510Q		Elna Silmic II
2	3.3	50	Blue (LC)	211513L		Nichicon FG
6	3.3	50	Grey		211513Q		Nichicon FG
5	10	16	Grey		211220Q		Elna Silmic II
3	10	50	Grey		211520Q		Elna Silmic II
2	33	16	Grey		211223Q		Nichicon FG
1	47	16	Grey		211225Q		Elna Silmic II
3	47	25	Light blue	211325V		Nichicon KZ
2	47	50	Light blue	211525V		Nichicon KZ
2	100	16	Light blue	211230V		Elna Silmic II
1	100	25	Light blue	211330V		Nichicon KZ
2	100	50	Light blue	211530V		Nichicon KZ
2	220	6.3	Light blue 	211032V		Elna Silmic II
2	220	25	Light blue	211332V		Nichicon KZ

1	22	16	NON-POLAR	215222N		Nichicon ES

2	10k	50	FILTER		213510Q		Nichicon KG
The blue and grey ones have "CE04W" printed on them. A quick google search reveals that it's most likely an old discontinued Nippon Chemi-con series. The light blue ones have a weird triangle symbol followed by the letters "CE". The single non-polar says "CE04D". The service manual also (incorrectly?) lists it as being 100 volt - I assume I should just get a 16 volt one, since that's what's in the amp?

The ones marked LC (blue sleeve) are listed as "ELECTROLYTIC CAPACITOR - LC" in the service manual - does this have any significant meaning? After all, both LC and non-LC are used to cover identical values so I guess there is some kind of difference.

Looking around the web for what caps to buy, the current idea is:
- Nichicon KZ as first priority.
- Elna Silmic II for all the values not covered by KZ.
- Nichicon FG to fill the rest.

Is this OK? It's all available from mouser.com. Two groups could have been Silmic II instead of FG (3.3uF/50v and 33uF/16v) but mouser don't carry these.

The main filter cap has three legs: positive, negative and ground. It's drawn as two separate caps inside a circle in the schematics. I assume two normal electrolytes with the same voltage and capacitance will do.

Also, is there anything to gain from slightly over-sizing the capacitance of the filter caps? Maybe 15000uF instead of 10000uF?

Thank you.

-- Anders
Attached Images
File Type: jpg cap_types.jpg (235.0 KB, 145 views)
File Type: jpg filter_cap.jpg (156.4 KB, 132 views)

Last edited by ironhamster; 24th October 2014 at 02:46 PM.
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Old 24th October 2014, 02:52 PM   #2
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I have updated the list with parts numbers from the service manual. The "LC" capacitors have a different letter in the end. Digging around a bit more, all four of them are used pretty much right behind the line in to the pre-amp and power-amp. (See attached pictures.) Coincidence?

I'm mainly concerned about this. Is is OK to just use regular electrolytes (like Nichicon FG) here or do I need something special?
Attached Images
File Type: jpg preamp_input.jpg (63.1 KB, 119 views)
File Type: jpg poweramp_input.jpg (56.6 KB, 119 views)
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Old 24th October 2014, 05:52 PM   #3
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Default Inter-stage caps ?

Hi ironhamster,

I personally own a nice TRM-210 Nikko that I plan to tweak... this amp is a "tube like" design with small chemical capacitors as inter-stage coupling caps.

It seems to be the same structure on your amp, could you post your entire schematics so we can check ?

In this case, for such strategic places, a good option would be using the green bi-polarized "MUSE" Nichicon ES Series as it will lower the harmonic distortion... or even some polypropylene MKP caps for the lower values, if you have enough free place on your board...

My amp (partial... I own the full manual if somebody need it ) :
Attached Images
File Type: png TRM-210 partial.png (82.9 KB, 135 views)
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Old 24th October 2014, 07:00 PM   #4
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Hello Leglandu,

Thank you for replying. The schematic is available from hifiengine.com. If you don't want to register I have uploaded a copy here: http://foob.dk/public/hifi/hfe_nikko..._schematic.pdf. I can't attach it since it's too big.

Nichicon ES could cover the same places as FG. It wouldn't be a problem using bi-polar caps here when the originals aren't? Forgive my ignorance, but where are the strategic places?
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Old 24th October 2014, 07:47 PM   #5
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Hi ironhamster,
I do a lot of renovation and modernization of old amplifiers.
I can give you some recommendations.
You need to watch scheme.
I would recommend to replace the capacitors on the polypropylene film - C601 and C602 -1m
C611 C612 -1m
C703 and C704-1m
Cascade at Q501 Q502 - Delete. Unsolder R519 R509, R520 R530. Connect a wire from the switch S1 (c) point "C" and S2 (a) poit "S" & S1 (b) point "C" and S2 (c) poit "S"
Remove all other parts cascades Q501 Q502.
Important capacitors is C617 C618 C619 C620 C709 C710.
The rest of the capacitors for general use.
Dubbed C1 replace two 15-18 000m - will be very good.
Write a personal message - I will be glad to help.
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Old 24th October 2014, 07:58 PM   #6
glen65 is offline glen65  United States
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Quote:
Originally Posted by ironhamster View Post
Hello people,

I'm about to recap an old Nikko TRM-750 amplifier. It exhibits a lot of symptoms in the sound that could point to the capacitors being bad. Two of them are visually leaking and some look like their tops have been extruding.
You didn't say what sort of issues you were having, but some may not be solved by just replacing the caps. Given the amps age there could be multiple sources which account for the trouble you are having with it. Just be prepared for that possibility.

Quote:
I'm a total beginner at this stuff, so I'm essentially just posting my game-plan here in the hope that someone is kind enough to tell me if anything is completely wrong.
Do you have any experience at all working with electronics?

Quote:
The goal is not to restore its original "vintage-sound" but to have an amplifier that sounds as good as possible by modern standards - within a fair budget of course.
The capabilities are dependent on the overall design of the amp. Changing the worn out
components will not transform the amp into something it wasn't designed to be.


Quote:
The main filter cap has three legs: positive, negative and ground. It's drawn as two separate caps inside a circle in the schematics. I assume two normal electrolytes with the same voltage and capacitance will do.

Also, is there anything to gain from slightly over-sizing the capacitance of the filter caps? Maybe 15000uF instead of 10000uF?
They don't need to be the same voltage.
To try and match the physical size, it might be necessary to look at a higher voltage rating.
I would do that first before going to a higher value. For example, you could replace a 63 or 80 volt cap with 100.
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Old 24th October 2014, 09:50 PM   #7
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Quote:
Originally Posted by ironhamster View Post
Hello Leglandu,

Thank you for replying. The schematic is available from hifiengine.com. If you don't want to register I have uploaded a copy here: http://foob.dk/public/hifi/hfe_nikko..._schematic.pdf. I can't attach it since it's too big.

Nichicon ES could cover the same places as FG. It wouldn't be a problem using bi-polar caps here when the originals aren't? Forgive my ignorance, but where are the strategic places?
Thanks for the schematic, ironhamster... I called these strategic places (capacitors) because they are just in the direct travel of the sound, they must block DC and let pass AC (the sound) without any distortion, what old chemical polarised caps do poorly.

Now, I have to apologize as I first have not realized that some of your caps must be urgently changed and of course are the REAL "strategic" problems to be solved... sorry !!!

So... my following tips are just about tweaking the amp, when everything else is fixed

C501 - C513 - C515 - C519 - C801 - C619 - C703 / C502 - C514 - C516 - C520 - C602(802?) - C620 - C704 are concerned

ES Muse have a different technology and their bipolarisation is totally compatible if you take care to get the same voltage :

Nichicon nichicon muse Condensateurs électrolytiques aluminium ? traversant | Mouser

You have the values 0.47, 1 and 3.3 uf in 50 V for exact replacement. These caps are very small, 5 x 11 mm for the 3.3 uf.

Polypropylene caps (MKP) are possibly better but are x10 bigger and also x10 more expensive...
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Old 25th October 2014, 12:49 PM   #8
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Quote:
Originally Posted by glen65
You didn't say what sort of issues you were having, but some may not be solved by just replacing the caps. Given the amps age there could be multiple sources which account for the trouble you are having with it. Just be prepared for that possibility.
Quote:
Originally Posted by glen65
Do you have any experience at all working with electronics?
I know it might not fix all the problems but replacing the electrolytic capacitors is probably something I can do myself, and it doesn't seem to be too expensive. I don't know much about electronics apart from basic stuff, but I'm pretty handy with a soldering iron.

The problems are: A bit muddy sound. One channel is slightly lower than the other and also a bit more distorted. One channel also only comes on after giving the volume knob a twist and warming up a bit. It crackles when you do it. Really, really low frequencies also crackles a bit. Then there's some noticeable hum and noise when the music is quiet.

Quote:
Originally Posted by glen65
To try and match the physical size, it might be necessary to look at a higher voltage rating.
I would do that first before going to a higher value. For example, you could replace a 63 or 80 volt cap with 100.
The main filter cap will have to be replaced by two caps since it's a weird 2-in-1. I'll most likely have to make some improvised mounting, so I'm guessing it would be best to just get the exact voltage.


Quote:
Originally Posted by Andreas AVM
I can give you some recommendations.
Hi Andreas. Thank you for the suggestions. I might try two 15000 uF caps for C1. I will keep the rest in mind for later. For now I dare not start doing more than simply replacing components with their exact values.

Quote:
Originally Posted by Leglandu
C501 - C513 - C515 - C519 - C801 - C619 - C703 / C502 - C514 - C516 - C520 - C602(802?) - C620 - C704 are concerned
Cool, thank you. The updated list would then be:
Code:
Qty	uF	Volt	Replacement	#

2	0.47	50 (LC)	Nichicon ES	_c515, _c516
1	0.47	50	Nichicon ES	c901	
3	1	50	Nichicon ES	_c513, _c514, c908
2	3.3	50 (LC)	Nichicon ES	_c703, _c704
6	3.3	50	Nichicon ES	_c619, _c620, _c501, _c502, _c519, _c520
	
5	10	16	Elna Silmic II	c611, c612, c617, c618, c905
3	10	50	Elna Silmic II	c705, c706, c727
2	33	16	Nichicon ES	c507, c508	
1	47	16	Elna Silmic II	c907
3	47	25	Nichicon KZ	c728, c729, c732
2	47	50	Nichicon KZ	c730, c731
2	100	16	Elna Silmic II	c709, c710
1	100	25	Nichicon KZ	c726
2	100	50	Nichicon KZ	c707, c708
2	220	6.3	Elna Silmic II	c717, c718
2	220	25	Nichicon KZ	c625, c626

1	22	16 (BP)	Nichicon ES	c725

2	10-15k	50	Nichicon KG	c1
(Your suggestions being prefixed with underscore.) Are you sure about c801 and c802? They are 0.01uF mylar caps and ES only goes down to 0.47.

Silly question: I plan to only replace one, at most two, caps at a time and check the sound each time. It seems the big filter cap has resistors in parallel so it will discharge fairly quickly, but what about the rest of the amp? How long should I wait before it's safe to work on again?
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Old 25th October 2014, 01:33 PM   #9
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the subject is getting long and in a way over analyzed....

to begin with take a read here ...written in a very simple language :
vintage amplifier repair/upgrade manual

Expect any capacitor that you change in your amplifier to do "something"
all changes will have some impact in the perceived result . Though the impact will be hardly noticeable and often hardly measurable

Alike will go the quality of capacitors ...there will be impact but hardly noticeable

To make noticeable difference you have to approach the problem in another way ...

1) beef up to anything available depending on the size to all capacitors in secondary power supply before regulation
2) like wise for the main filter power supply
3) then spend your time to see how much will help bypassing those capacitors and skip the plan of listening to the changes one by one capacitors ( it will end nowhere brain cannot file properly or keep track of the changes so you will end up in a 3 year ghost chase ( at least )

Noticeable difference in an existing circuit can be only made by changing or altering if you like parameters of the amplifier
gain , speed , bandwidth and bias

Problem is that many things can be made to do that but any alteration in the above conditions will have a direct impact in the safety margins of your amp

Bottom line is that this cannot be done from a NB and will require knowledge and instruments to evaluate the changes properly

What can be done by a NB that will be harmless is
---Complete recaping good quality but no extremes
---Proper cleaning switches pots and so on
---Relay replacement if one exists in the output
---Bypassing of psu capacitors ( will require bit of experiment )
---Replacement of DC blocking capacitors with film but this will work well only if you can find film caps that fit the value and physical size ( no bigger pitch than 5mm so its 0.47-1.0-1.5-2.2 uf at the most )
---Verification of bias offset and anything measurable in your amp according to the SM

Kind regards
Sakis
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Old 25th October 2014, 02:20 PM   #10
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I feel my comment about wanting it to sound as good as possible was a bit unclear. Sorry about that. I don't want to start changing the values to something other than the specified. (Except maybe the main filter cap). I was referring to the quality of the replacement components and the different brands and series. In this case the electrolytic capacitors. I would like it to sound at least as good as in its original state. And if the tone is not quite the same, due to new components, that's OK.

Quote:
Originally Posted by east electronics
3) then spend your time to see how much will help bypassing those capacitors and skip the plan of listening to the changes one by one capacitors ( it will end nowhere brain cannot file properly or keep track of the changes so you will end up in a 3 year ghost chase ( at least )
The rationale for doing it this way was to make it easier to backtrace my steps if I screw up somewhere. Thank you for replying. I will read your guide.
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