Hum from Yamaha CA-1000 and from speakers?

rjsilva

Active Member
A hum is coming from my CA-1000 which I'm sure didn't exist previously. The same hum also comes out of the speakers, which definitely wasn't there. It's a new unit for me and it had problems when I first got it, so I didn't have much time with it before this problem, but again I'm sure it wasn't there.

It sounds like the power transformer - when I lived in the UK I had a power converter to use 120V electrics, and this sounds a lot like that. It's fairly quiet from the unit, a little louder from the speakers, and is not affected by volume.

The only thing I did to the unit before noticing the hum was replace the output transistors (with Onsemi). I guess it could be a cooincidence, but I'm hoping someone has some insight.

Thanks!
 
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Capacitors, diode bridge, bad ground somewhere?
Is the transformer emitting a mechanical hum?
 
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Yes, it is emitting a mechanical hum (with a bit of a buzz). I was hoping it was the outlet because I had moved the unit to another one, but I moved it back and it has the same thing. Sometimes the noise is a bit louder for a second when unit turns on, like there's a bit of a surge.
 
Did you fold down the rear panel of the amp to work on it? There is a little wire with a screw connecting the rear panel to the bottom of the chassis. Check this connection.
 
The two biggies are:
1) loose screw holding power transformer down (or something metal within it's field)
2) grounding issue, which can include bad caps.

You got your work cut out for you...
 
Yes, it is emitting a mechanical hum (with a bit of a buzz). I was hoping it was the outlet because I had moved the unit to another one, but I moved it back and it has the same thing. Sometimes the noise is a bit louder for a second when unit turns on, like there's a bit of a surge.

Sometimes the noise is a bit louder for a second when unit turns on, like there's a bit of a surge.
"Inrush Surge"The CA-1000 doesn't have a "soft start" so this is quiet possible and common occurence, But a hum in the speaker(s) indicates a power supply issue if the hum is in both speakers.The issue could be a bad ground connection or a filter capacitor passing a bit of AC.Take a good look at the power supply board on the bottom side of the amp.Better yet post a photo of the component side.Take a close look at the six caps clustered together.I will replace all caps on this board, every time with 105 degree units...Look for plastic label shrinkage or swelling/bulging.Also can't rule out the two largest caps on the topside of the amp.

BTW the picture is of a CA-800 the 1000 has a very similar board.
 

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Thanks for the replies! I'm feeling like I want to say "uncle" with this amp :)

The power supply is screwed in nice and tight and it appears ok - the only thing I can think of is that the metal thing that loosely surrounds it gets caught quite badly when removing the wood casing. It has no apparent damage, and I doubt that'd cause a problem. I hadn't removed the back so if the wire connecting the rear panel to the chassis shouldn't have come off.

I'll examine and take a photo of the power supply board. One of the large capacitors on the top side does have a sort of bulging on the top - it looks/feels like plastic that's not quite fitted properly. I didn't think anything of it previously. I'll take a pic of that too.
 
The tops of those large black capacitors that can be seen from the top of the unit are usually bulged from the plastic shrinking over time. You should be able to press down on it with your finger and feel a flat hard area - thats the top of the aluminum cap itself. They will vent out of the bottom before they make the aluminum at the top warp - to the best of my knowledge those particular caps are not manufactured to fail from the top like most smaller caps are.
 
I do see some plastic label shrinkage, not sure if it's a problem but I've attached some pictures (I didn't include the large capacitors because of xoaphexox's post).

I have some new information:

1) The volume pot doesn't affect the hum/buzz in the speakers, BUT the Audio Muting switch does reduce it.

2) Class A has more hum/buzz from the speakers than class AB, but I'm uncertain about from the actual power transformer.

I'm wondering if this problem could have caused the ECG281 short? And if so, since that happened after I cleaned the unit I'm wondering if it's something I inadvertently did...
 

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I would recap that power supply board - there is evidence of those caps being stressed for sure. Not saying this will definitely fix the issue but it is important if you planned to keep the amplifier running well for the foreseeable future.

As a side note, the two CA-1000 I have restored have both had fusistors on either side of that group of large caps. Looks like you have some non-flammable metal oxide resistors in there - was this amp worked on in the past? Maybe a production change by Yamaha themselves. Not an issue, just a curiosity of mine.
 
That blue colored diode has been changed ,the OEM diodes looked like the black round one beside it.and the fusistors as well have been replaced. But those three caps look pretty beat.I'd recap the entire board.:yes:
 

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My one CA-1000 has that same blue diode on the board, but my board is labeled:

LC65130
NA06332

My other CA-1000 has the black diodes like in his picture and the same label as the one in his picture.

Is it possible it was a mid-production change? How can I determine the date code with these units?
 
Thanks guys, I really appreciate it! I'm not sure when I'll get to it, but hopefully soon.

Are there any recommendations or tutorials for removing the glue, and what glue to use when putting the new ones in?

BTW, on a side note, would it be worthwhile to replace the fusistors on the driver boards with regular resistors? These ones being changed made me think of it.
 
Removing glue is easily done with and exacto chisel blade.
 
None , not required...:no: Glue was used to steady/support larger components for automated assembly line wave soldering.
 
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In response to your fusistor question, you already tested the fusistors and only found one to be close to going out of tolerance. If you want to alleviate yourself of any future worry you could replace them with new metal oxide resistors. Or you could just leave well enough alone. If you choose to replace them you must use non flammable one - no carbon resistors.
 
I ordered capacitors for the power supply board and the driver boards. I couldn't find a Panasonic for the larger capacitors so I ordered a Nichicon and wondered if I made a good choice. It is for the 80V 220uf cluster of four and here's the one I ordered:

http://www.mouser.com/ProductDetail/Nichicon/UPM1K221MHD6/?qs=Otuxy0mHUQDtE8ughLUQWg==

Nichicon has their audio capacitors and this isn't one of them, so I was a little concerned. However, the only other brand Mouser had was United Chemi-con and the data sheet talked about computer storage equipment.

Was it an acceptable choice?
 
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