CA-810 hum

try1256

Super Member
I have recently developed an audible hum coming from my CA-810. Not through the speakers, from the unit. I figured it was transformer hum. I removed the cover and the transformer was pretty hot. A couple of days ago, I opened it up to check and adjust the idle current and I noticed when the amp was sitting on its end, it didn't hum. That night afterward, I didn't hear a noticeable hum. Now it's back. Is there anything else that can cause a hum like that? Thanks :music:
 
I have recently developed an audible hum coming from my CA-810. Not through the speakers, from the unit. I figured it was transformer hum. I removed the cover and the transformer was pretty hot. A couple of days ago, I opened it up to check and adjust the idle current and I noticed when the amp was sitting on its end, it didn't hum. That night afterward, I didn't hear a noticeable hum. Now it's back. Is there anything else that can cause a hum like that? Thanks :music:

Try torquing down the Xformer mounting fasteners.
 
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I removed the cover and the transformer was pretty hot.

Hi,

Did you also check AC voltages? You should have ~30VAC with blue (via 2x fuses) and green (secondaries), and ~34VAC with red and black to the rectifiers, according to SM.

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Hi,

Did you also check AC voltages? You should have ~30VAC with blue (via 2x fuses) and green (secondaries), and ~34VAC with red and black to the rectifiers, according to SM.

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I did not do that. Do you check each wire to ground or between the two wires?
 
Hi try1256, please keep us updated. My CA-810 also has a light hum from its transformer. It's only audible when there's no music playing, so to me it's not really disturbing.
The only thing I checked where the screws, but they were all tightened.
 
Hi,

Did you also check AC voltages? You should have ~30VAC with blue (via 2x fuses) and green (secondaries), and ~34VAC with red and black to the rectifiers, according to SM.

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I couldn't find the color wires but looked in the service manual. It shows 3 wires coming out of the transformer 30v on either side and a ground. It measured 32.5v. Not sure about the red and black. I may be at the limit of my ability here. I am sure it could use a complete restoration, just not in the cards right now.
 
Does your unit have voltage selector or is it fixed at 110V? or 120V?

viecrn.jpg


Please, try to have actual AC voltage from the red and common black secondary wires (to the rectifiers) as well. They come out together with the other 2 blue and green wires. They are wrapped in pins next to the first rectifiers at right.

1s0do0.jpg


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Mine doesn't have the voltage selector. It's a U.S. model. What does 32.5v out of the transformer indicate?
 
the red and black are reading 36v. I still don't see a green wire with the blue. I checked the voltage at the 2 points on the other side of the board where the transformer connected. also, with the idle voltage set at 20mv on both sides, the R O test point shows 2mv not 0mv. Power Supply issues?
 
2mV at R0 and L0 is fine.

Looking at secondaries you should see a green wire going to the power amp board via under that middle metal frame that holds the 2 white fuse sockets. The 2 blue wires go to the fuses (sockets).

36V shouldn't be an issue. It's only 2V of variation. How "hot" does your transformer can get?
 
My transformer looks different than yours in the picture. I don't have wires coming from that side. They all come from the other side and there was not a green one in any of the bundles I can see.

It can be touched without burning your hand but it is very warm. It's funny, I had it sitting on the end to check these voltage readings and there was no hum. I checked the mounting screws and they are all as tight as possible. The amp sounds very good, no issues there. I just get a bit obsessive about some things.
 
My transformer looks different than yours in the picture. I don't have wires coming from that side. They all come from the other side and there was not a green one in any of the bundles I can see.

It can be touched without burning your hand but it is very warm. It's funny, I had it sitting on the end to check these voltage readings and there was no hum. I checked the mounting screws and they are all as tight as possible. The amp sounds very good, no issues there. I just get a bit obsessive about some things.

Okay, I should have known that: your unit is a fixed 120V, so the transformer is different from the multi-voltage ones we have here.

Anyway, my unit also had a hum at beginning, but because it was set at 220V, IIRC. I set it for 240V. Unless the hum turns louder and louder, your unit seems ok.
 
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