Noisy LC3 motherboard

[Unknown_K]

Years ago I scored 2 LC3's on freecyle. One worked fine and still works fine to this day, the other worked for about 15 minutes making noise from the speaker (whistle) and when shut down never turned on again.

So the other day I washed it and let it dry in my basement, and tonight I replaced the (5) 47uf 16v aluminum capacitors. When I tested it it bonged and booted, but there is still a slight whine coming from the speaker (you have to listen to hear it). I ordered 10uf caps (think there are 4 of those) and some 100uf to completely redo the rest of the aluminum capacitors. What I want to know is which type is coupled to the sound chip that could be making noise (the 47uf I replaced or a different one)?

I have been using a different LC format motherboard in that case (68040/25 with FPU and heatsink) so when I finish this project I might just sell of the LC3 motherboard if anyone needs a recapped and cleaned one.

 

[Yoshihide]

The four 16v 10uF capacitors on the top left are the ones that are related to the sound chip. (http://450.servehttp.com/reference/caps/, the 2nd picture from the bottom.) Replacing the 10uF capacitors have resolved "squaking" noises in both my Performa 450 (LC III) and LC II.

If the sound is low, then you also need to replace the 6v 100uF.

 

[Unknown_K]

The four 16v 10uF capacitors on the top left are the ones that are related to the sound chip. (http://450.servehttp.com/reference/caps/, the 2nd picture from the bottom.) Replacing the 10uF capacitors have resolved "squaking" noises in both my Performa 450 (LC III) and LC II.If the sound is low, then you also need to replace the 6v 100uF.

Thank you very much, waiting on a package with both those parts to finish the recap job and hopefully the noise will be gone.

 

[Unknown_K]

Capacitors arived and I did the rework, noisy speaker went away and the sound is good and loud now.