LC squeaking

[JRL]

While an pizzabox LC is turned on, it emits a squeaking sound which eventually fades over time. What's wrong?

 

[meall]

Maybe the fan needs lubrification?

 

[JRL]

Hmmm... I'll swap out the fan from my own dead LC then.

 

[meall]

As far as I can tell, the fan is the only moving part in an LC. So it is either that, or some kind of transistor that going to died, difficult to say from your problem's description.

 

[JRL]

I really have a feeling it's the fan.... The cords appear to be damaged in some way.

 

[pee-air]

As far as I can tell, the fan is the only moving part in an LC. So it is either that, or some kind of transistor that going to died, difficult to say from your problem's description.

The LC also has a floppy drive or two and/or a hard drive. My Quadra 700 squeals briefly when I power it up as well. I attribute the squeal to power draw on startup. If I run the Quadra with a beefier power suply, there is no squeal.

 

[JRL]

I am going to try to replace the fan and see what happens. It could be power draw, but I switched PSU's with no change.

 

[pee-air]

Just disconnect the fan for a moment and power the sucker up. No point in replacing the fan if it's not the source of the squeal. In my Quadra 700 I have a CPU fan that gets its power from the hard drive connector. If I disconnect the fan and power the machine up there is no squeal. If I disconnect the hard drive and leave the fan connected, there is no squeal when I power up. If I connect them both, I get a squeal until the hard drive completely spins up. The hard drive draws more power on spin up than it does once it's up and running.

 

[LCGuy]

What monitor are you using, and have you tried booting it up without the monitor? My LCIII has always had a 14" Macintosh Colour Display (14" Apple Trinitron that does 640x480, very common on LCs) since we got it new in 1993. In 1999 we noticed it started making a squealing sound, which at first I thought was either the HDD or the fan, since the display sits on top of the computer. It was the monitor. (its a common issue with these displays)

That one blew up in 2001, but since then I now have another MCD, which has the same issue. So yeah, before doing anything with the computer, try and rule out the monitor first, especially if its an MCD.

Also, it could be the bearings in the HDD.

 

[JRL]

The monitor is a '12 RGB; I tried two of these with no change.

 

[sylwiusz]

My LC makes similar sounds and for sure it is not fan, because I have disconnected it :-/ Seems like a problem with logic board.

 

[porter]

Have you considered the switch mode power supply? They working by using high frequencies that stabilise after the loads settle.

Is it an electronic or mechanical squeak?

 

[tomlee59]

I just noticed this thread -- what seems to be missing is a discussion of where the noise is coming from. Is it emanating from the speaker? Is it coming from someplace else? The source of the sound will be an important clue as to its cause, needless to say. It could be this, it could be that, it could be any of the things people have mentioned, but a systematic investigation of the source itself should precede any substantial repair effort.

 

[Scott Baret]

This problem seems to be pretty common with pizza box LCs. I've seen it in Is, IIs, and IIIs.

It's not the hard drive. Nor is it your fan. I've even tried swapping power supplies to no avail. My guess is that it's got something to do with the logic board's connection to the power supply, since the sound I have heard seems to originate there. (Unless, of course, the extra power supplies I've got are all bad too).

I've got an LC I'm working on right now and will try swapping the power supply with one from a known working LC 475 that doesn't have this problem. If it works, then the conjecture is that the power supply is the problem. Otherwise, it's a logic board issue (perhaps pertaining to the power supply portion of the board, similar to what the standalone analog board on a compact Mac is).

 

[LCGuy]

I'm curious - do capacitors make any noises like this as they start to go out? I'm thinking...maybe it could mean the caps are on their way out...

 

[Franklinstein]

Big ones will. Ya know how a camera will emit a high-pitched whine when it's charging the flash? That's coming from the charge capacitor. So other high-capacity caps will also emit a squeal or squeak from time to time, particularly if they're old or overloaded.

 

[tomlee59]

The noise from a flash charging is from the inductor/transformer, not the capacitor.

Capacitors can make sound, but much more rarely and softly. The core materials used in inductors and transformers are magnetostrictive (i.e., their dimensions vary with the applied magnetic field). Also, the windings can change shape as the magnetic field varies. Many transformers are dipped in goo to dampen the audible noise (and to reduce sensitivity to moisture, etc.).

Capacitors have plates that are separated by such small distances that, even if the plate separation were to modulate as a function of applied electric field, the sound emitted would be feeble.

Failing electrolytic capacitors can generate electrical noise -- a steady voltage can produce currents that vary randomly, crackle, pop, whistle, chirp, etc. If these capacitors are in the audio signal path, then the electrical noise can turn into audible noise.

 

[Charlieman]

I'm curious - do capacitors make any noises like this as they start to go out?(

The small caps on logic boards fail silently (apart from the disruption that they cause during the process). Big caps in power supplies provide very few subtle warnings and go BANG. We bought a bunch of PCs with bad PSU caps (BANG!) for student teaching areas.

By BANG! I mean that fragments shot out of the back of the PC and could have caused facial or eye injury. Fortunately, the first failure was observed by an electrical engineering lecturer, so we immediately took the report seriously. In private testing (ie without a class of students), a couple of PSUs failed in a similar way, so our supplier fitted a different batch of power supplies.

*Edit* Apple PSUs very rarely go BANG. Once, in my experience of using thousands of Macs, and that might have been might fault by not waiting long enough before booting a Mac that had been in long term storage. But I've seen a couple of WOOFs of flame from compact Macs. Tom Lee denies this from his experience, but it might be a difference between 110V and 220V compacts.

 

[LCGuy]

Oh yes, Charlieman, I've had a couple of AT and ATX PSUs do that, but also a Power Mac 8100 power supply back in 2002.