Yamaha MX800 recap?

A

Audio Kiva

New Member
My good old MX800 developed a very audible AC hum. Two of the large filter cans seem 'out of spec'. (Have not removed yet) I am looking for replacements but everything these days seem not to fit.... Advice on sourcing electrolytics spec'd 27000uF, 42v and 25000uF, 50v-- no bigger than 50mm diameter, 80mm tall.
Also, please advise if suitable substitutes of higher values exist somewhere in America???

THanks ,
Pete
 
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Don't know the MX-800, some guys in the yamaha subforum will know.

Is it 50/60Hz mains hum (it which case unlikely to be main caps) or rectified 100/120Hz???
Mobile phone ap like spectroid or pc freeware audacity can measure.

Yeah it could be a failed rectified diode letting in 50/60Hz or tired filter caps causing increased ripple (100/120Hz) or maybe a failed voltage regulator (100/120Hz)
 
mbz said:
Don't know the MX-800, some guys in the yamaha subforum will know.

Is it 50/60Hz mains hum (it which case unlikely to be main caps) or rectified 100/120Hz???
Mobile phone ap like spectroid or pc freeware audacity can measure.

Yeah it could be a failed rectified diode letting in 50/60Hz or tired filter caps causing increased ripple (100/120Hz) or maybe a failed voltage regulator (100/120Hz)
Click to expand...

Yeah, some sorta diagnostics would be nice. Plenty of "I recapped it but didn't fix the problem" threads.
 
whoaru99 said:
Yeah, some sorta diagnostics would be nice. Plenty of "I recapped it but didn't fix the problem" threads.
Click to expand...
Yeah. I am presuming the hum comes from the power /rectification stage. I can only see significant differences in the main caps from in-circuit testing. My DMM on responds up to 20,000uF. Two of these caps are showing much less than that (2030 and 13336 on another)
 
Audio Kiva said:
So increasing capacitance and voltage is OK?
Click to expand...
Yep, keep in mind the OEM caps were +/-20% (or worse). Also modern cap manufacturing has improved to the extent that some aim for -5% to -10% to save costs, still within the +/-20%. Increasing voltage will get slightly improved ripple handling
 
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