Yamaha C-1 Preamp - Phono Section Problem

bhuskins · Jul 21, 2015

I've got a nice C-1 preamp that works great on the all the inputs except the 3 phono inputs which have a noise issue in the left channel. The right channel is like you'd expect it...nice and quiet when nothing is connected. A slight hum at high volume but that would go away once a table is grounded to the input. The left channel has what I suspect is a noisy transistor(s). That typical scratchy and hissy sound bad transistors make. The meter also shows this noise in that channel and the noise follows the controls if you reverse L and R or combine, etc. All 3 phono inputs exhibit the same problem. I'll likely go through the entire unit eventually and fully restore it, but for the short term I'd like to resolve the noise in the left channel on the phono section. Any advice on what board/section/part(s) I should focus on to get this unit working properly?

clinic-audio · Jul 21, 2015

YAMAHA C1 Phono section problem

Hello bhuskins

Send me a PM if you want .

This is not to be mad with you but I don't think you will be successfull in C1 repair

This last year I have refixed 4 YAMAHA C1 with original components . You have to know perfectly the unit and what you are doing inside .

If you never did it before don't even try . You may risk to dammage some PCB who was working before you put your hands in .

The best way to act would be to ship me your board for repair but it is up to you .

Some other AK members did it and they can type their opininon here

PATRICE

bhuskins · Jul 21, 2015

I appreciate the offer but before I consider something like that I would like to hear about what it possibly could be. I have a pretty narrowly focused issue and likely you and others that have put their hands on a C-1 for service have seen this issue. Hopefully, you can see where I'm coming from as well being that I've restored hundreds of other units and I'm not exactly a rookie here. So, before I throw in the towel and ship you a board to go through I'd like to at least explore the issue in theory.

clinic-audio · Jul 21, 2015

OK

I understand your point of view but you have to know that the unobtanaible TR 2SK78 , 2SJ24, and LJ13 are very fragiles

see my picture of a "working" 2SK78 after I take it off the pcb ! I am aware of that but this do not avoid me troubles ....

see my previous post

http://www.audiokarma.org/forums/showthread.php?t=526450

bhuskins · Jul 21, 2015

Yes I've definitely read through all the great C-1 threads including the one showing the fragility of the 2sk78 and other transistors you linked above. At this point I'm not touching anything and would just like to discuss in theory the issue. Any actual repair attempts would be discussed in detail before I attempted anything. Knowing that unobtainable parts are scattered around the C-1 is what prompted me to post in the first place versus attempting to shotgun replace a bunch of transistors and making the situation worse.

avionic · Jul 21, 2015

Highly recommend sending it to Patrice. I sent one a while back.With no phono out period.. Got it back working like it should.:thmbsp:

clinic-audio · Jul 21, 2015

Giving you a guide is very difficult ....

With all C1 I had for repair , none was making the trouble you describe ...

You can make a good start by changing all the b-polarized cap of 47MF/6,3V .

I saw many times some transistors with " pealing legs " ( see my pictures ) see if you have any ....My pictures show 2SC1345 but this does exist with other types . I don't think that this is the cause of your trouble but if you work inside the unit , this will be a good "cleaning job " to do .

bhuskins · Jul 21, 2015

On which board(s) do all the phono functionality reside? Are you talking about all the 47uf BP 6.3v throughout the entire unit or just on the phono section? I'm sure eventually all will get replaced but I'm tackling the repair first. Since there's not a phono independent board...that's why I ask.

for_p1 · Jul 21, 2015

bhuskins said:
On which board(s) do all the phono functionality reside? Are you talking about all the 47uf BP 6.3v throughout the entire unit or just on the phono section? I'm sure eventually all will get replaced but I'm tackling the repair first. Since there's not a phono independent board...that's why I ask.

You need to start with obtaining service manual with schematic and boards layout.

avionic · Jul 21, 2015

Its just one board. NA06714 ( EQ board)

avionic · Jul 21, 2015

for_p1 said:
You need to start with obtaining service manual with schematic and boards layout.

:yes: All the freebie manuals are piss poor resolution. I have the HQ scat blown up 24" X 36" and its still handy to use a magnifier lense.

bhuskins · Jul 21, 2015

I've got a full rez service manual...don't leave home without it!

bhuskins · Jul 21, 2015

avionic said:
Its just one board. NA06714 ( EQ board)

Ok...that's good to know...I'll do visuals on that board to see what I see. I suspect a nichicon muse 47uf BP cap would be a good choice for those replacements?

avionic · Jul 21, 2015

E-mail Norman and tell him what you need.

http://www.analogalley.com/m_yamaha.htm

He will send you a HQ pdf . for 13-15 USD.

He is my Go-to for manuals. KEY : E-mail and ask !

bhuskins · Jul 21, 2015

Just for manuals correct? Not the parts? I think our messages crossed each other...I already have a nice high resolution copy of the service manual. I was still wanting a suggestion on the 47uf BP caps though...nichicon muse is what I'd usually use but didn't know if there's a better choice for this unit?

avionic · Jul 21, 2015

bhuskins said:
Just for manuals correct? Not the parts? I think our messages crossed each other...I already have a nice high resolution copy of the service manual. I was still wanting a suggestion on the 47uf BP caps though...nichicon muse is what I'd usually use but didn't know if there's a better choice for this unit?

If you have a manual..disreguard..

I'd use "EP's" due to the amount of heat. But thats me.

http://www.mouser.com/Passive-Compo...N-75hqw?P=1z0z7l5&Keyword=nichicon+EP&FS=True

for_p1 · Jul 21, 2015

Probably he needs low leakage type there. Service manual should have special notes on that.

avionic · Jul 21, 2015

for_p1 said:
Probably he needs low leakage type there. Service manual should have special notes on that.

47µf/6.3 vdc Bi-polar --- bi-passed with polyester films.

bhuskins · Jul 21, 2015

I've got nichicon muse and ep on hand so I guess I need to decide...what would the bypassed polyester film be?

for_p1 · Jul 21, 2015

I looked at circuit. It is rather compex. I would not recommend working with it without enough knowledge and access to metering gear.

Yamaha C-1 Preamp - Phono Section Problem

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