[Spliff]

I've got an iMac G3 (600 Mhz) that's recently developed a high-pitched squeal. It only occurs when the computer is cold, after booting up or waking up from sleep. After 15-30 minutes (when the computer has warmed up), the squealing vanishes.

I thought it might be the hard drive. I ran various disk media utilities and the drive checks out fine. The squealing really seems to be coming from the back of the CRT. I did a search in google and came across a mention of dried out capacitors. Dunno what those are or why they would cause squealing.

Two other things. One, the CRT has be degaussing itself a lot recently. Two, when the computer is squealing, there are horizontal distortion ripples running along the bottom of the display that disappear when the squealing stops.

Anyone take a guess at what's causing this?

[Spliff]

I did some more googling and came across a forum post that mentioned the flyback transformer as a possible source of the squealing. Either the transformer could be failing or there could be too much dust accumulated on it. I don't know what a flyback tranformer does.

Using compressed air, I did my best to remove the dust. In the process, I blew off a chunk of red insulation from some copper wire that wraps around the base of the CRT. The insulation looked dried out and cracked.

Removing the dust had no effect on the squealing. Instead, the squealing is worse. It changes in pitch depending on what colors are displayed on my screen. Dark colors cause a higher pitched squealing. In addition, I now have constant moire lines and distortion ripples on my screen.

Looks as if my iMac is basically f**ked. No chance of selling it now. When it dies, I'll have to cannabalize it.

[f1000]

Originally posted by Spliff:
I've got an iMac G5 (600 Mhz) that's recently developed a high-pitched squeal. It only occurs when the computer is cold, after booting up or waking up from sleep. After 15-30 minutes (when the computer has warmed up), the squealing vanishes.

iMac G5 (600 MHz) with a CRT?

[diehlr]

A lot of voltage regulation circuits oscillate/switch at super high frequency to prevent being audible. Over time, when parts such as capacitors and transistors begin to wear out, it can cause the oscillation frequency to periodically drop and do weird things. When it drops down into the human audible spectrum of frequencies is when you begin to hear it. In other words, the circuit is always making noise, it's just so high pitched that you don't notice it. The wiggling side effect could also be due to a bad capacitor.

[f1000]

I'm going to take a stab in the dark here, but CRT TV's have a degaussing circuit that only comes on when the TV's been cold for awhile. Maybe your CRT is getting stuck in degauss mode until the degauss thermistor warms up enough to cut off the circuit. If this is the case, you might be able to replace the thermistor yourself.

[Spliff]

Originally posted by f1000:
iMac G5 (600 MHz) with a CRT?

LOL. It should be "G3." Wishful thinking on my part.

[mikemako]

I have a MDD Powermac (G4 1.42GHz) with two 80GB western digital hard drives in it. My computer also has a high-pitch squeal when it first starts up or when it wakes from sleep. I'm pretty sure it's the hard drives. They are new drives so I'm fairly certain they're not going bad or anything.