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| My LC III wants to be a DJ. |
Posted by: Lateralus on 2008-10-28 16:48:14
When powered on, my LC III intermittently emits whining noises in varying tones through its speaker. I've swapped the speaker to no avail.
The kicker is that if I touch miscellaneous chips on the motherboard with varying degrees of pressure, I can alter the pitch and repetition rate of the whine.
Why is my LC III a beat machine?
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Posted by: porter on 2008-10-28 16:53:03
Why is my LC III a beat machine? Beats me!
My LC II and III both make whining noises which I assume are coming from the PSU which subside after a few minutes, I assume that they are merely going supersonic rather than actually abating.
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Posted by: Lateralus on 2008-10-28 16:57:20
You might wanna check. I assumed mine was the PSU as well, but it's definitely the speaker.
Once on, it goes quit every now and then only to start the whine again a few seconds later. Definitely not something that being powered on for a while cures.
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Posted by: porter on 2008-10-28 17:08:26
Could be noise on the power rails then. Do you have a similar machine you can swap components with to eliminate them from your inquiry? Eg swap PSU etc.
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Posted by: Lateralus on 2008-10-28 17:14:15
Nope. I run a tight ship nowadays.
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Posted by: Dennis Nedry on 2008-10-28 20:19:06
Most likely it's bad capacitors on the logic board.
I have one that does this too from the speaker. It sounds like an old AM radio.
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Posted by: Lateralus on 2008-10-28 21:16:37
The board looks perfect, top and bottom. So I don't know.
Maybe my IIci spread a disease to it while they were in the closet together this past year...
Regardless, I'm more willing to screw with the LC III to keep it viable than I am the IIci. The LC III, majestically sitting next to a garbage can as I passed by on the walk home from school one day, won my heart and brought me over from the dark side.
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Posted by: FakeWozniak on 2008-11-28 17:56:14
I just got an LCIII from ebay and it has that whine/hiss/am radio noise too.
From my hardware background, I would think it was a failed capacitor too. I've noticed that while it oscillates audibly, the actual sounds going over the speaker (Apple Menu -> Control Panel -> Sounds, then clicking an alert sound like Quack) will be garbled. I would suspect the problem is isolated to the audio driver. Maybe something like a 555 Op Amp or a supporting capacitor.
Anyone isolate this further? If so, please post! I will post what I find.
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Posted by: superpantoufle on 2008-11-29 03:07:19
Don't we have twice the same problem here?
From what I understand, one could merge those two threads. Two of my pizza boxes (a LC and a LCIII) alsa wanted to become DJ's lately. It seemed to be some RF interference (from the AC board?) in the speaker. Does the noise stop when you plug in headphones?
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Posted by: indibil on 2023-03-08 09:16:12
I know it's been a long time since this post, but I have an LC3 with the same noises. I have changed capacitors of the supply and of the motherboard, and they are still there.
Has anyone figured out what causes these noises?
Thank you. |
Posted by: ymk on 2023-03-08 10:31:37
I also had oscillation after recapping.
Changing C4 to 47uF solved it for me. |
Posted by: mikes-macs on 2023-03-08 16:23:30
It’s a mystery to me. I have never heard of this problem before now. It was usually the Mac IIsi that had all of the sound problems. I’ve got a Performa 400 with no sound issues at all. Perhaps you got some device in your home that causes interference. |
Posted by: Daniël on 2023-03-09 02:10:25
I'd guess the DFAC (digitally filtered audio chip) would be at fault. They tend to die from cap leakage, and can do weird things when damaged/dying like noisy sound, intermittent sound, extremely weak signals, etc. |
Posted by: bibilit on 2023-03-09 04:47:24
Most likely it's bad capacitors on the logic board. I agree a 100%, this screeching sound is generated by bad caps. |
Posted by: indibil on 2023-03-09 09:22:00
I also had oscillation after recapping.
Changing C4 to 47uF solved it for me. Thank you so much! I have replaced the new 10uF C4 with another 47uF one and the noise is gone!!!!
It can't be the fault of anything in my house because I have another LCIII that doesn't have that problem, with the factory capacitors. |
Posted by: ymk on 2023-03-09 10:58:55
Thank you so much! I have replaced the new 10uF C4 with another 47uF one and the noise is gone!!!!
Glad it worked for you 🙂
Another thing LCIII owners should be aware of: C22 polarity is reversed on the silkscreen. |
Posted by: mikes-macs on 2023-03-09 11:00:28
I was hoping your Mac could DJ a retirement party next weekend? How can I re-create this on mine? |
Posted by: indibil on 2023-03-10 09:46:20
Glad it worked for you 🙂
Another thing LCIII owners should be aware of: C22 polarity is reversed on the silkscreen. Yes, i have put C22 reversed, i know this 🙂 |
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