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Whistling Mac Classic II

T

tezza

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I know Macs can play music but I have a Mac Classic II that whistles. It's the one I'm trying to re-install an OS on in another thread.

The whistle usually starts with a very high pitch then sinks down to a low buzz...then disappears. They is will randomly appear again sometimes going from low to high, or again from high to low? It doesn't seem to affect the screen or functionality (at least, yet!). Sometimes it might go for 30 mins without whistling. It seems to do it more when it's cold.

I have two working Mac Classic 2s so I can swap out components. At first I felt this would be some large cap/thing on either the video board, tube, PSU or even associated with the hard drive. But no, it's actually from the (small) mainboard at the base??? Either it's FROM there OR that board CAUSES some other part of the machine to whistle.

I haven't yet determined exactly what's whistling. It's hard to locate. I need a stethoscope! It's certainly loud enough though. Point is...the whistling follows the mainboard!!??? The mainboard only has some ICs and mini-caps.

Anyone come across this symptom before? It's not critical for me, as the whistling Mac is a spare I want to sell...I'm really curious to know what it is though! (and it will probably sell better if it didn't make this rather alarming noise).

Tez
 
Motors can do that too. Since you're having trouble with the internal hard disk you might try disconnecting the power/cable to that and see if that's doing it. Suppose it could also be the monitor. Do you have a stethoscope? You can use the old engineer trick of a screwdriver to pinpoint noise too (put your ear to the plastic and the metal around the plastic case (obviously not on anything that would short) but that may help you get closer to the problem area.
 
It could be the monitor. Some of my older monitors aggravate me with the high pitched squealing. How long does the squealing last? But since you said it was the board making the sound, could it be some sort of capacitor?
 
DOS lives on!! said:
It could be the monitor. Some of my older monitors aggravate me with the high pitched squealing. How long does the squealing last? But since you said it was the board making the sound, could it be some sort of capacitor?
Click to expand...

Yes. I also thought it was the monitor as I've heard other TVs sound similar. But I swapped mainboards and the sound is now coming from the machine I swapped with!?? The donor machine (with a replacement mainboard) is now fine. Whatever the problem is, it travels with the mainboard (and only the mainboard). This is what makes it so puzzelling? The capacitors on the mainboard are tiny!

The squealing is not constant. It either starts very high then steadily reduces in tone, or it starts low, then steadily increases until the pitch is beyond human hearing. Each "event" lasts about 10-20 seconds.

Tez
 
It's bad capacitors; specifically, those around the audio section. It's referred to as the "falling bomb sound," and is a common problem with compact Macs and the LC series. Sounds like now is the right time to do a recap!
 
Chuck(G) said:
Like this?

Seems to be because of bad capacitors; said to be alleviated somewhat with a good bath (the Mac, not you):

http://68kmla.org/forums/viewtopic.php?t=4406&highlight=
Click to expand...

LOL, yes that's exactly it Chuck and glitch.

The old capacitors on the mainboard problem eh! Well, that would figure. I've had to wash a Classic II board in the past to get it to boot due to leaking caps. I didn't realise they sang as well. Time to fire up the dishwasher again methinks.

Thanks for the pointer.

Tez
 
From that video, it sounds like the sound was more or less coming from the mainboard on the bottom, rather than the monitor. Tezza, does that video look (and sound) like what's happening to your Mac Classic?
 
DOS lives on!! said:
From that video, it sounds like the sound was more or less coming from the mainboard on the bottom, rather than the monitor. Tezza, does that video look (and sound) like what's happening to your Mac Classic?
Click to expand...

Yes, I'm sure that's the problem. Bad caps around the audio section. That would explain it.

Much obliged guys.

Tez
 
My Color Classic just experienced this exact problem - a loud whining noise that I first thought was a failing HDD bearing, but after replacing the HDD I discovered it was actually coming from the speaker. The noise was accompanied by a smell that must have been leaking electrolyte. Looks like there's some goo near the C4 and C5 caps, which appear to be bulging. The C9, C10, and C11 caps also look questionable, so I'll probably just recap the entire board.

I'm considering using either polymer caps or tantalum caps for their longer life expectancy. I was actually using this Color Classic for writing so I really want it up and running again ASAP. Will report the results.
 
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Follow-Up: I've re-capped my Color Classic with Nichicon tantalum surface-mount caps and all is well. Very glad that DigiKey sells these things in small quantities. The hardest part was extracting the old electrolytic caps - I used two soldering irons to melt the solder on both ends simultaneously, but they were still stubborn about sticking to the board. I cleaned the electrolyte from the mainboard using alcohol and q-tips.

Incidentally, replacing the caps also seems to have fixed the problem of the system refusing to power-on until it had been plugged into the wall for several hours. Now it powers up immediately upon being plugged in.

68KMLA has a very helpful Wiki on this subject:

http://68kmla.org/wiki/Capacitor_Replacement
 
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