Need help identifying resistors on C-65

jethis

New Member
Hello all, I have a newbie question that I hope someone in the Yamaha forum might be kind enough to help me with. I just purchased a C-65 preamp in very good cosmetic condition from Salvation Army for $20.00. Got it home and found that the volume was very scratchy and the left stereo channel did not work at all, although the right channel works and sounds excellent. I spent hours cleaning the board and resoldering the RCA inputs, but this did not restore the sound in the left channel. Upon taking a closer look at the board, I noticed that some glue around the heatsinks had spilled over onto the board and turned into a nasty crust, completely enveloping two resistors. While I could not locate a schematic for the C-65, I found one for the C-85, which appears to have the identical heatsink configuration. In the C-85 schematic, the two resistors are labeled "R271" and "R272." The parts pages in the back of the service manual did not list these two parts, and I am unable to identify them by color since they were so badly damaged, so I am hoping someone might be able to tell me what replacement parts I need to get. I have attached a photo showing where the two resistors would go on the board.
 

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C-80/85 is --------

4.7KΩ 1/4 watt yellow-violet-red
 
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Hello all, I have a newbie question that I hope someone in the Yamaha forum might be kind enough to help me with. I just purchased a C-65 preamp in very good cosmetic condition from Salvation Army for $20.00. Got it home and found that the volume was very scratchy and the left stereo channel did not work at all, although the right channel works and sounds excellent. I spent hours cleaning the board and resoldering the RCA inputs, but this did not restore the sound in the left channel. Upon taking a closer look at the board, I noticed that some glue around the heatsinks had spilled over onto the board and turned into a nasty crust, completely enveloping two resistors. While I could not locate a schematic for the C-65, I found one for the C-85, which appears to have the identical heatsink configuration. In the C-85 schematic, the two resistors are labeled "R271" and "R272." The parts pages in the back of the service manual did not list these two parts, and I am unable to identify them by color since they were so badly damaged, so I am hoping someone might be able to tell me what replacement parts I need to get. I have attached a photo showing where the two resistors would go on the board.

It you still have the glue encrusted resistors.Measure there resistance with a multimeter....
 
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Thanks Avionic! I still have one resistor, but it was pretty badly damaged. The other one might be less damaged but it got sucked up when I was vacuuming the crust off the board. I'll try to find that one and see if I can test either one of them. If I can't get a viable reading off the multimeter, I'll just pick up some resistors with the ratings you gave me and see how it goes.
 
Took me a couple of weeks to get back to this project, but here's an update. I replaced the resistors and even bought some machine screws to attach the heatsinks to the PCB. Resoldered everything and fired it up and now it sounds fantastic. The left channel is completely restored and this preamp is back in business. Not bad for a total investment of less than $25.00 (including cost of the unit). The volume pot is a little scratchy when I raise or lower the volume, but I'm not sure if I should mess with it. Also, the sound through headphones is fine, but I am wondering if I should replace the large caps on this unit as a lot of others have done based on my reading in this forum. Will it really make that much of a difference in sound? Or should I just leave it "as is" and be happy with what I've got?
 
Took me a couple of weeks to get back to this project, but here's an update. I replaced the resistors and even bought some machine screws to attach the heatsinks to the PCB. Resoldered everything and fired it up and now it sounds fantastic. The left channel is completely restored and this preamp is back in business. Not bad for a total investment of less than $25.00 (including cost of the unit). The volume pot is a little scratchy when I raise or lower the volume, but I'm not sure if I should mess with it. Also, the sound through headphones is fine, but I am wondering if I should replace the large caps on this unit as a lot of others have done based on my reading in this forum. Will it really make that much of a difference in sound? Or should I just leave it "as is" and be happy with what I've got?

Reflow all the solder connections on all those copper buss bars as well.

The largest caps may be difficult to find in a easily useable physical size.
 
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