Help diagnosing Kurzweil Mark 5 - powers up, all lights normal, but no sound


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Hi there,

I have a Mark 5 that I purchased new >20 years ago, which until recently worked flawlessly. However, now I find that when I turn it on, all appears normal but no sound comes out - either from the speakers or if you plug in headphones. All lights are operating, I can make any selections I want using the buttons, etc. If I turn the volume slider all the way up I can hear the faint white noise I normally did. Otherwise there is no sound when the keyboard is operated, the Demo button is pushed, etc.

I have already tried the reset methods I've found online with no change. With no success with that, I have largely disassembled the unit and performed a variety of other steps:
  • Removed the two metal shields and examined all capacitors for signs of bulging or leakage, damaged ICs, etc. - none found
  • Confirmed all fuses are intact
  • Unplugged, cleaned with contact cleaner, and reseated all plugs/jacks (under shielded areas and under the keyboard itself)
  • Cleaned volume slider pots and confirmed resistance changes with movement of the slide
I have a multimeter (how I checked resistance & continuity across fuses), so am happy to do any other checks that would be recommended. I would welcome any assistance in trying to get things back up and running. Again, I've never had any issues with this unit so I remain hopeful it something simple that can be replaced or repaired.

Thank you!
 
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happyrat1

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Take a mono earphone and attach probes to the end.

See if you can trace the signal along the audio path to see if the problem is with the audio section or the logic section.

If the problem is with the CPU logic it may cost more to fix than it's worth.

Gary ;)
 

happyrat1

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And eyeballing the capacitors is not a sure fire method of determining leakage.

What you need is an ESR meter to check them out in circuit.

They cost about $50 on ebay and amazon.

Gary ;)
 
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Update: I managed to acquire a Service Manual and have performed all the diagnostic tests. The result of that is that it seems the analog circuits on the Engine board is likely at issue. I'm happy to have ruled lots of other things out but now need to try to find a schematic. Support won't give me one of course, even though it's a d/c'ed product.
 
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