Help with Yamaha tuner/amp

[matticus]

I recently got this Yamaha cr-400 tuner/amp and I am getting distorted audio out of the unit. seams to be in the spk out section because headphones sound fine. I took a few pictures of the board and what I believe is some bad filter caps. I have never seen caps leak this type of material. If anyone can let me know if those caps are the issue that would be great.

also tips for cleaning old dirty pcb's would be awesome!

Thanks for your help!!

 

[matticus]

Here is a link to the schematic download in case anyone needs it.

http://www.hifiengine.com/manual_library/yamaha/cr-400.shtml

Thanks.

 

[KrisBlueNZ]

Thanks for the link to the service manual but we can't download it unless we sign up. Could you upload it somewhere where we can get it without signing up.

The brown stuff on the filter caps is glue, deliberately put on heavy components to relieve strain on the solder connections.

Edit: Welcome to Electronics Point

 

[matticus]

thanks for your reply KrisBlueNZ, here is a link to the service manual. https://www.dropbox.com/s/8l0vnv0303dyrnv/hfe_yamaha_cr-400_service.pdf?dl=0

 

[matticus]

I have checked my DC offset, was at 45mV, adjusted it and got it down to 5mV but that didn't help the distorted audio. could there be a problem with the output transistors? The solder joints on those transistors look to be fine though.

 

[matticus]

just cleaned all pots and the spk selector switch, still getting distorted audio. any help would be awesome!!!

Headphone output sounds great if that helps anyone.
Thanks

 

[KrisBlueNZ]

The headphone output is taken from the power amp output. If the headphone output is clean, that implies the power amp is OK as well. So check the speakers themselves for damage or deterioration. Also try connecting external speakers instead of the internal ones.

 

[KrisBlueNZ]

Sorry, that unit doesn't have internal speakers. So, try different speakers with it.

 

[matticus]

Sorry, that unit doesn't have internal speakers. So, try different speakers with it.

I have tried multiple different speakers with the unit. Anything else you can think of?

 

[matticus]

I bypassed the speaker selector switch and audio still sounds distorted. I connected a speaker directly to the headphone out put off the board as well and it sounds distorted just like the regular speaker output.

 

[KrisBlueNZ]

Do you have access to an oscilloscope? Or even a computer that can record from a line-level audio input? Capture the waveform across the speaker terminals, ideally with a resistive load connected, and at low and medium volume settings, with a sinewave of say 500 Hz feeding the AUX inputs. You can generate a sinewave using Audacity or some other waveform editor, and play it back while you record the amp's output.

 

[matticus]

I don't have a scope but I can do your other suggestion. A picture of a 500Hz wave form is what you are looking for im guessing?

 

[KrisBlueNZ]

Yes, something like that. A sinewave. Try it at low volume and medium volume