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Yamaha DSP A1 surround channels mute from time to time

Hi,
I am experiencing a specific problem on my gloriosus DSP A1.
When I switch it on the right surround channel is mute and some times also the left surround channel and (one time also the central channel).
If I encrease the volume louder and louder the mute channel start to sound with a bad initial "crack sound". After that the channel works fine.
I suppose it's a cold welding problem or an electrolitic condenser problem. And it is affecting the 3 effect channels only.
How can I fix it? Thanks in advance.

Comments
Ambrosia Heart
Ambrosia Heart picture

When I switch it on the right surround channel is mute and some times also the left surround channel and (one time also the central channel).
First make sure if ALL channels are mute sometimes.  In your case, it seems relays problem due to a layer of  black oxide called
Ag2O affecting the contact conductivity. Open ALL speaker relays, removing black oxide by glasses repairing screwdriver.

If I encrease the volume louder and louder the mute channel start to sound with a bad initial "crack sound". After that the channel works fine. Time needs for oxide to allow 
electrical signal to pass through if an oxide layer is not too thick.

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Max Cap
Max Cap picture

Thanks a lot. I'll do my best to identify the speaker relays in the service manual and to clean them.

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