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LC III popping speakers and unusual behavior
- Thread starter fyndr
- Start date
fyndr
Well-known member
That might be a bit more expedient. I have CRC CQ electronic cleaner which I can use to spray both sides of the board before baking. I guess I don't have any silicone spray for after I bake it though, is that strictly for the process to work or is it more of a nice-to-have step?
Elfen
Well-known member
Electronic Cleaners are usually a Flux Stripper and not a Cap Good Cleaner. The only way to remove Cap Good especially if it is under the chips is with Ammonia/Distilled Water (then dry), then acetone (then dry) and then alcohol (and then dry). Ammonia will neutralize any acid the Cap Goo has, Flux remover does not do this and is usually an acid itself to cut the resin the solder flux is made from.
After it is dry then you can bake it.
The Silicone Spray is to protect the board after is has been cleaned up and id working again (or repaired that it is working again) as it will prevent moisture from penetrating the board. This depends on the environment you are in. For me being a salt & polluted air of NYC, the moisture in the air is corrosive and the silicone spray will protect the board. I would say that any place in the USA would need this as (thanks to China and other nations creating a lot pollution) our air is contaminated with stuff that can corrode a board in a few years time.
After it is dry then you can bake it.
The Silicone Spray is to protect the board after is has been cleaned up and id working again (or repaired that it is working again) as it will prevent moisture from penetrating the board. This depends on the environment you are in. For me being a salt & polluted air of NYC, the moisture in the air is corrosive and the silicone spray will protect the board. I would say that any place in the USA would need this as (thanks to China and other nations creating a lot pollution) our air is contaminated with stuff that can corrode a board in a few years time.
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CC_333
Well-known member
fyndr
Well-known member
A quick update, I tried an amalgam of what Elfen and Uniserver were suggesting since I don't have all materials readily on hand. I cleaned the board all over with CRC QD electronics cleaner, waited for it to dry, then cleaned the areas around the sound chip, audio jack, and speaker connectors with 91% isopropyl alcohol and a spare toothbrush. Once that had all dried off, I used Pledge (I checked the ingredients and it does contain silicone oil) front and back on the motherboard and then put it on a pizza pan in the oven for 15 minutes at 220 degrees Fahrenheit. Turned it off and opened the door, then 15 minutes after that put it back into the case and plugged everything back in.
Now it doesn't appear as though there's any sound at all. The speaker no longer pops, it just make no sound whatsoever. I checked the audio jack as well with a pair of earbuds, although it makes some crackling when I put it in or out, no actual sound from the system can be heard there either. It looks as if the whole computer has gone mute.
I'm not sure what to check next. The power supply seems solid and the fact that both the speaker and the audio jack don't work point to something within whatever controls the LC III's sound in a general sense, either the audio chip or some trace coming off of it. I'm not familiar with PCBs and don't really know how to troubleshoot if it is a broken trace or something else (I'm not even strictly 100% sure of what the audio system consists of, to be honest) but if anyone has any suggestions I will try to carry them out as best as I can.
Now it doesn't appear as though there's any sound at all. The speaker no longer pops, it just make no sound whatsoever. I checked the audio jack as well with a pair of earbuds, although it makes some crackling when I put it in or out, no actual sound from the system can be heard there either. It looks as if the whole computer has gone mute.
I'm not sure what to check next. The power supply seems solid and the fact that both the speaker and the audio jack don't work point to something within whatever controls the LC III's sound in a general sense, either the audio chip or some trace coming off of it. I'm not familiar with PCBs and don't really know how to troubleshoot if it is a broken trace or something else (I'm not even strictly 100% sure of what the audio system consists of, to be honest) but if anyone has any suggestions I will try to carry them out as best as I can.
techknight
Well-known member
I think you have a chip/op-amp failure. I had a feeling about that since the beginning.
fyndr
Well-known member
I've uploaded a few more pictures of the relevant area here:
http://imgur.com/a/dPFLF
I noticed there are some markings that may be from the Pledge that I used to spray the board down before baking. I'm assuming that's a normal consequence of the silicone oil? Otherwise I might try cleaning again with 91% isopropyl alcohol and a toothbrush again.
Regarding the audio chip, I'm assuming it's the one in the upper left-hand corner labelled "9325AN 344S1003-8 (M)© 90APPLE 136365"? Is there a way to determine if this is a failure with the chip itself, and if so, what can be done to fix it?
http://imgur.com/a/dPFLF
I noticed there are some markings that may be from the Pledge that I used to spray the board down before baking. I'm assuming that's a normal consequence of the silicone oil? Otherwise I might try cleaning again with 91% isopropyl alcohol and a toothbrush again.
Regarding the audio chip, I'm assuming it's the one in the upper left-hand corner labelled "9325AN 344S1003-8 (M)© 90APPLE 136365"? Is there a way to determine if this is a failure with the chip itself, and if so, what can be done to fix it?
Elfen
Well-known member
The big chip in the upper left (9325AN 344S1003) is I believe part of the PDS Slot decoding. What you need to look two small chips towards the bottom right (U5 and U6). As Techknight said, it could be an op-amp (audio amplifier) chip failure or the leads going to them. U5 looks like it still has crud on the upper pins. Trace and check the leads to it and to U6.
U5 and U6 (I believe) are the op amps, which takes the signal from the Sony Sound Chip and makes it louder. Since it is in Stereo AND the LCIII has Audio In and Out, there are two of them. Thing is I did not see a Sony Chip on my LC III Boards so it must be inside the GLU or Eagle Chip. But continuing on with what Techknight said - check that area around those chips (U5 and U6) and their traces.
Uniserver - to me, C4 looks like its fine to me. It's the upper area of U5 that has me concerned.
U5 and U6 (I believe) are the op amps, which takes the signal from the Sony Sound Chip and makes it louder. Since it is in Stereo AND the LCIII has Audio In and Out, there are two of them. Thing is I did not see a Sony Chip on my LC III Boards so it must be inside the GLU or Eagle Chip. But continuing on with what Techknight said - check that area around those chips (U5 and U6) and their traces.
Uniserver - to me, C4 looks like its fine to me. It's the upper area of U5 that has me concerned.
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fyndr
Well-known member
@uniserver I sent you some closeups of C4 in a PM a few weeks ago but here is a fresh set of pictures from today:
http://imgur.com/a/kr3vU
As far as I can tell C4 is soldered correctly, insofar as the connection between the cap and the pad appears to be contiguous, but I'm not an expert on solder joints so can't say for sure.
@Elfen Thanks for the information on the sound chips. Like I said I'm not familiar with working with PCBs so I'm not sure how I would be able to trace where the leads go apart from visual inspection. Is there a way to check the traces using a DMM?
In the meantime I'll try using alcohol to clean up U5 and U6 and check the sound again once it is completely dry.
http://imgur.com/a/kr3vU
As far as I can tell C4 is soldered correctly, insofar as the connection between the cap and the pad appears to be contiguous, but I'm not an expert on solder joints so can't say for sure.
@Elfen Thanks for the information on the sound chips. Like I said I'm not familiar with working with PCBs so I'm not sure how I would be able to trace where the leads go apart from visual inspection. Is there a way to check the traces using a DMM?
In the meantime I'll try using alcohol to clean up U5 and U6 and check the sound again once it is completely dry.
techknight
Well-known member
Nope, thats the DAC.
I see some trace/via rot near the vicinity of the DAC, so that needs checked out first...
Also, the 2nd up-close pictures are about as useless as can be without a clear macro lens. Try again...
fyndr
Well-known member
A quick report, I cleaned up all of the regions around the DAC, the caps and other chips in that region of the board with alcohol and let it dry. The speakers are popping again, but I can't seem to make any sound come through apart from that. Also tried applying gentle pressure to the board near the chip but didn't notice any effect. I'll try heating the joints of C4 with my soldering iron when I have time tomorrow.
techknight
Well-known member
Your going to have to go oscilloscope tracing on this one.
crackling and popping means the DC-Offset from one of the op-amps is jumping all over the place.
crackling and popping means the DC-Offset from one of the op-amps is jumping all over the place.
fyndr
Well-known member
Okay well I managed to dig out my old soldering iron and tried melting the joints on either end of C4. I think I succeeded although my iron is kind of fat on the end so it's a bit cumbersome trying to get at that cap without nudging against other components on the board. I booted the machine and it gave off a short shriek before the sound came back to normal, however it appears that the popping/crackling still occurs at intervals. I'm not sure if this means the joints need further work or if it's just a fluke of the op-amps.
Speaking of, I don't have an oscilloscope and based on the prices it doesn't look like I'll be getting one anytime soon. I'm pretty much just limited to the basic tools I have available to me, which as far as hobbyist stuff goes is the DMM and soldering iron. If there's a way for me to troubleshoot this issue further using those tools and the information I've provided so far in this thread, please let me know, otherwise I will have to call it a wash and live with the sound issue as it stands.
Speaking of, I don't have an oscilloscope and based on the prices it doesn't look like I'll be getting one anytime soon. I'm pretty much just limited to the basic tools I have available to me, which as far as hobbyist stuff goes is the DMM and soldering iron. If there's a way for me to troubleshoot this issue further using those tools and the information I've provided so far in this thread, please let me know, otherwise I will have to call it a wash and live with the sound issue as it stands.
Elfen
Well-known member
Strange and maybe related discovery....
Today I turned on my Semi-Dead LC475, and it popped, squealed and eventually after warming up, made a fast 'putt putt' motorboat sound. For a second I thought my LC475 finally gave up the ghost. Damn...
It turns out that it was the PSU crapping out, and not the LC 475 board. When I tried the LC475's PSU on another LC board, it gave the same action. But when I put a known good PSU into the LC475 - it chimed happily and then that's it (because that is all it can do, chime up but no video and no disk access, so there is something more to the board than just what it seems.)
Thus I'm thinking, can this be a PSU problem here too? And what would it need, other than a basic recapping, to fix it? Only way to test it now is to use a known good LC PSU on your machine.
Good luck.
Today I turned on my Semi-Dead LC475, and it popped, squealed and eventually after warming up, made a fast 'putt putt' motorboat sound. For a second I thought my LC475 finally gave up the ghost. Damn...
It turns out that it was the PSU crapping out, and not the LC 475 board. When I tried the LC475's PSU on another LC board, it gave the same action. But when I put a known good PSU into the LC475 - it chimed happily and then that's it (because that is all it can do, chime up but no video and no disk access, so there is something more to the board than just what it seems.)
Thus I'm thinking, can this be a PSU problem here too? And what would it need, other than a basic recapping, to fix it? Only way to test it now is to use a known good LC PSU on your machine.
Good luck.
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