Yamaha MX49 No Sound

Synth Repair
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Hi Good People, I have an MX49 that was fine for years but sadly now has no sound on any of the outputs. Everything else appears to be functioning properly. Running an AUX signal in produces no sound out either. Checked all the cabling, seems seated.

Looking at the audio jack board I noticed two of the electrolytic caps C610 & C604 had the bulging tops and replaced them with no luck. The opamps have 9vdc on the supply pins. I’ve done a factory reset as well.

I do not have schematics currently but if someone would be kind enough to let me know what connector pins I could probe to verify if an audio signal is present or where the DAC output is to the audio card that would be much appreciated or what else to check. Thanks in Advance Albert

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BTW, I was able to locate the Service Manual :grinning_face: whew this is a big help. I’ll be able to poke around with some confidence now. But of course in the meantime any thoughts or input would be welcomed.

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Ok, fortunately I was successful in restoring the MX49’s sound output. The JK board or audio/jack PCB had two additional failed electrolytic capacitors, C630 & C662. These were in the bias circuits for both the L & R channels amp inputs (IC601).

Kinda surprising that both failed around the same time. Anyway this is an intermediate amp stage that drives both the L/R outputs and feeds the Headphone amp. So it makes sense now why there was no output at all.

Perhaps this will help someone in the future.

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I am just getting around to reading this. Glad you fixed and good job! I was buried in troubleshooting a Yamaha CLP-340 with no sound for months. The detailed specs that Yamaha provided were helpful. I will keep this in mind if one of my clients show up with the MX49

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