Duo 280c Inverter Board Whining

[jmacz]

I'm still working on a Powerbook Duo 280c and it's coming along nicely.

But there was this whine coming from the screen when I received it. And unfortunately, I had hopes it would go away once the unit was fully recapped (screen, inverter, logic board) but unfortunately, the whine persists.

The frequency of the whine changes with the brightness and is completely gone if the brightness is turned all the way down (ie. backlight is off). Disconnecting the backlight makes it go away, but that doesn't tell me much as that's the same as when the brightness is turned all the way down. It's hard to narrow down based on listening, but it's not coming from the LCD or the fluorescent backlight tube. It's coming from the inverter. The inverter board has two coils, and it's coming from the larger one I believe.

I've dealt with coil whine on power supplies before, usually using hot glue or something to prevent the coils from vibrating. But I'm not sure if it's the same problem and the coils on the inverter board already seem to have some type of epoxy or something on them.

Anyone deal with this before?

 

[jmacz]

Ok, problem solved, for now.

Again from past experience coil whine is due to the high frequency vibrations in the coils and the "fix" is to dampen or prevent that vibration from happening. Hot glue worked for me in the past on power supplies but that's with larger coils. The inverter board however has really tiny coils and I did not think hot glue would be effective. Searching online, seems some folks have used superglue instead (has to be the liquid form, not gel, as it needs to fill in any voids between the coils). I put some on and let it dry over night. This morning, the whine's gone. Hopefully it stays that way.