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Repair Yamaha HS8S Subwoofer output

AlBundy100

May 5, 2022
4
Joined
May 5, 2022
Messages
4
Hi folks,

I have been happily using a HS8S sub with a pair of HS8 monitors for about two years. The right speaker output from the subwoofer has recently died. I swapped cables and played sounds on different monitors to confirm that the monitors themselves are fine.

A visual inspection of the circuit boards does not reveal any obviously blown capacitors. I don't want to spend an insane amount of time debugging faulty components in a circuit for a device which costs $500 new, so I am hoping I can simply replace either the amplifier PCB or I/O PCB assembly and one of them will have the bad part on it.

Unfortunately the service manual for the HS8S does not appear to be anywhere online. I can order it from uad.net (here) but I found the service manual for the previous subwoofer generation, the HS10W here, which appears similar in design. Page 21 shows me roughly what the replacement parts are called for the HS8S. Searching ued.net again, I found the replacement boards for the HS8S: https://i.imgur.com/YYORWOK.png (link)

They are fairly cheap (relative to replacing the entire unit) at $34 each.

Now to my question: Which board, the I/O PCB or the Amp PCB is more likely to cause the broken monitor output line? I am heavily leaning towards the I/O assembly, but its possible the audio is routed to the Amp assembly to perform filtering before being sent back for output.

Thanks for your time.
 

AlBundy100

May 5, 2022
4
Joined
May 5, 2022
Messages
4
A Yamaha tech walked me through the circuit on the service manual and said replacing the I/O board is my best bet (wow, incredible support by Yamaha). I'll post an update here after I get it installed.
 

AlBundy100

May 5, 2022
4
Joined
May 5, 2022
Messages
4
Hi there, please check my last update from May 11 - the new IO board indeed fixed the unit.
 
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