iBook G3 noises

[enryfox]

Hi,

I'm trying to silence my iBook G3 (snowwhite, dual USB) and after replacing a noisy HDD, I'm left with what seems electronic noise.
It is an intermittent high pitched hiss coming from the upper left side of the main board, near the CPU area. It sounds like noise coming from a switching circuitry but the odd thing is it completely disappears if I pause my mouse on the control panel Item in the apple menu.
Is it a sign of something dying or can it live with that ?

thanks
bye 

[DieHard]

If you find that you need to disassemble to inspect or repair... we have the manual here:
http://macos9lives.com/smforum/index.php/topic,3204.0.html

[enryfox]

Thanks for the service manual !
Actually I have already disassembled the iBook to replace the HDD and internally it is in good order, quite clean with no damaged cables or missing parts.
I do not know what might be causing the hiss noise but it very likey comes from electronics...

bye
Enrico

[nanopico]

I'm not the best with hardware issues like this, but it sounds like something related to an inverter for the back-light which would be a switching circuit.

[enryfox]

I'm not the best with hardware issues like this, but it sounds like something related to an inverter for the back-light which would be a switching circuit.

I thought that too, but the display inverter is in the opposite position to where the buzz/hiss noise seems to originate. Removing the keyboard, the noise increases and it is from the CPU/GPU area. I think it might be something related to the throttling of the CPU for energy saving, but I only hope is not the sign of something on the brink of failure..

thanks
bye

[DieHard]

It is not uncommon for failing electronics (or oxidation on contacts) to emit "noise".  Many Power supplied with blown caps sound like a dog whistle. The steps I would take on your unit would be.. in order

1) First, I definitely like the "replace inverter board" suggestion since they are very often a source of issues when failing, even if the noise is NOT coming directly from it, it may be causing other components to generate noise if it's voltages are way out of spec.

2) Dis-assemble, use expensive contact cleaner (like $35 a can); this stuff is safe to spay on the boards and contacts directly, this one is the absolute best, but most expensive
http://www.jensentools.com/ms-730-contact-re-nu-12-oz-aerosol-miller-ste/p/593-463

A cheaper alternative which is about 80% as good (but much cheaper)
http://crcindustries.com/ei/product_detail.aspx?id=05103&S=Y

3) re-seat all components after cleaning, and pay special attention to any shields being in the proper place,  iBooks, iMacs, and many other Apple products have EMF shielding very specifically designed to stop interference between component, make sure you did not remove or fold back any shielding

Unfortunately, if all this fails, it could be the Logic board itself... disconnect speakers and get a USB sound card

[enryfox]

After further investigation, it is definitely the CPU throttling: if I let the display shuts down, the hiss is still there; if I set the CPU to reduced speed, the buzz/hiss changes; if I start a CPU intensive application (e.g. Duke Nukem 3D) any noise disappears...
Not sure if it is a symptom of an imminent failure, but I paid a few euros for the iBook and I will not spend more to replace the logic board. If it fails I will look for a "new" one

thanks
bye