LC III popping speakers and unusual behavior

[fyndr]

I've been maintaining what was formerly a fully operational LC III for the past couple of months following the completion of board and PSU recapping (c.o. Uniserver) but a few weeks ago I noticed that the internal speaker would occasionally make a popping noise. The issue seemed to get progressively worse until just a couple days ago when it ceased to make any sound at all, not even the startup chimes. This morning I tried to troubleshoot the issue and found that the audio jack in the back of the unit has the same popping issue as well.

I tried unplugging and reconnecting the speaker contacts, checking the jack to make sure there wasn't any debris/stuck contacts there, and used a slightly damp tissue to wipe down the areas near J2 and J15 on the motherboard (corresponding to the connection points for the audio jack and the internal speaker, respectively) in case there was some issue of cleanliness that I couldn't see. When I turned the unit back on, the sound seemed to act normally again, but this is where things went south.

I left the computer and came back 5 minutes later to find that the mouse wasn't responding. I tried plugging it in directly to the back of the unit (instead of daisy chaining it through the keyboard) and tried inputting keyboard commands but to no avail. I restarted the machine and it appeared to start up fine, but the popping speaker was back, and shortly after going to desktop a message came up saying 'Sorry, a system error occurred. "Finder" error type 10'. I clicked the restart prompt and the startup noise went off, but then the chimes of death played and nothing happened.

I unplugged everything and started the machine and it seemed to respond correctly, and upon replugging things in gradually, no other issues came up. Once everything was back to what it was before, the LC III started up to desktop correctly, but again the speaker pops intermittently. I left it on for a long while and nothing else untoward happened.

I'm not sure what is going on given that the behavior is unpredictable, but the only commonality appears to be with the audio popping. As stated before, the board and everything has been recapped as of late October, and presumably it was cleaned in the process. I don't see any capacitor discharge or anything like that although there are some small stains presumably from previous such leakage on parts of the board away from (I think) the parts responsible for sound. Is there a specific protocol I should be following to troubleshoot the issue further?

 

[MJ313]

It may be worth your time to re-wash the board. My LCIII got funky too after working well for awhile and after recap. I washed it and it returned to working great. There are some a bunch of threads about washing boards but if you want suggestions just say so. Anyway, it's a cheap and easy thing to do and can help get rid of residual cap goo that might be on there for whatever reason.

 

[fyndr]

Seems like a good idea and easy enough to do at home. I'm not familiar with PCBs but from what I've read the procedure for washing would be as follows:

1. Remove the PRAM battery and RAM stick from the motherboard

2. Detach the motherboard and put it in a tub or other container

3. Use 91% or better isopropyl alcohol and a toothbrush to go over the areas in contact with the PCB

4. Rinse off debris from step 3 using more alcohol

5. Dry off the motherboard using a fan or heater at a safe distance

6. Once completely dry, reinstall motherboard into chassis and put PRAM and RAM stick back

Is this rundown generally correct? I assume the same procedure could also be done with the extra RAM as well without modification.

 

[mwdmeyer]

After step 4 I would rinse with distilled water. When I just used isopropyl alcohol it left some white staining, not that it has caused an issue.

 

[uniserver]

hey there can you do me a few favors?

1. can you take a picture of the offending area,   area where the A/D is /  Speaker Amp,  Caps etc

2. can you possibly record what that popping sounds like?

3. can you with a meter tell me the Readings from your psu rails?   -5, +5, +12

4. does the A/D I/C there in the corner ever get hot? or even noticeably warm?

Thanks!

its odd that it works fine for couple months and then starts acting up.

I have had issues with Color Classic and some issues the kind of align with your issues there.

but usually it will show up with in the 2 hour burn in.  I'v had to replace the A/D before, especially once they start getting warm or even nuclear hot.

(i think the cap goo can cause irrversable issues with this I/C) just like the UE8 Issue with the SE/30. 

 

[fyndr]

Regarding the numbered items:

1. I'm not sure what A/D means specifically but I went ahead and took pictures of the relevant parts of the motherboard and then some. Let me know if higher quality pics are needed or if a specific area needs further attention: http://imgur.com/a/HrYCr

2. I made a recording of the speaker popping noise: http://vocaroo.com/i/s0zyss1Hiprs covers the cycle of turning on the machine (0:06s), the popping (0:18 to 0:25), and then turning it off (0:36).

3. I have a digital multimeter but honestly I have little experience using it and have only the barest idea of what you're asking. I'm a complete novice when it comes to circuitry although I'm trying to improve.

4. Still not sure what the A/D is, but regarding the board itself I hadn't noticed one way or the other about its temperature.

I'll try to clean the board at my next opportunity, but with the holidays fast approaching I probably won't have time for another week or so.

 

[uniserver]

thanks, ill send you a pm if i see anything that sticks out.

 

[Elfen]

2. I made a recording of the speaker popping noise: http://vocaroo.com/i/s0zyss1Hiprs covers the cycle of turning on the machine (0:06s), the popping (0:18 to 0:25), and then turning it off (0:36).

Wow... Interesting popping. To me it sounds like a PSU problem or you got a very noisy AC Voltage. Check the PSU...
 

3. I have a digital multimeter but honestly I have little experience using it and have only the barest idea of what you're asking. I'm a complete novice when it comes to circuitry although I'm trying to improve.

To check the PSU, put the black wire from the multimeter onto the metal casing of the PSU OR one of the 2 black wires in the harness and make sure it makes contact with the pin in the harness. Of course - turn on the LC III...

For 5V - put the red wire from the multimeter to the red wire in the harness. The Multimeter should read anywhere from 4.75 to 5.25 Volts, preferably at 4.9 to 5.1 volts. Looking at a LC PSU right now, there is no Red Wire, but it should be the Orange Wire that is 5V.

Now I forget which is which, I think the yellow wire is 12V and the Blue wire is -5V but it might be the other way around. Either way, when you measure those wires for voltage, you should get 11.75V to 12.25V for 12V - best at 11.9v to 12.1V; and -4.75 to -5.25 Volts, preferably at -4.9 to -5.1 volts.

The problem is this, if it is a cheap digital multimeter, you may get a rock solid steady reading of these voltages as the sampling rate might be low. If it a good multimeter with a higher sampling rate, then if you should get a reading that flutters about every seconds or so if there is a problem with the PSU. This is why I double check with an analog meter, it there is a flutter or spike (which I suspect here), you can see the needle shake much more visibly. A good PSU should have rock solid readings.

For me, this is either a PSU problem or a Noise in the AC problem. Working in schools, I seen a bad florence transformer muck up old Macs sound by adding spikes in the AC Line. When the transformer was eventually replaced, the offending noise in the Macs went away.

 

[techknight]

If you dont get a chime, which I didnt hear one, its very possible the sound IC is bad or traces to it are broken. 

Elfin: your not going to be able to watch the voltage rails with a DMM easily with popping like its doing, the voltage fluctuations would be too fast. You would need a decent oscilloscope to watch the rails for spikes. the spikes can cause the pops. especially if one of the filter caps in the PS didnt solder well, or anything really. Also any spikes in the 5V rail will glitch the CPU and cause all kinds of functionality madness. 

The DMM has a fairly slow response time unless its a high end fluke. If the DMM catches voltage fluctuations then the power supply is grossly faulty and you would be lucky the machine runs at all. 

 

[Elfen]

True Techknight. Fyndris is running with system failures as is.

Q (Without needing to look at my LCIII board): Is the Sony Sound Chip Apple uses on Macs on the LC III separate or has been integrated with other chips?

 

[techknight]

The sound dac is external i believe

 

[fyndr]

Thanks to everyone for the great replies. I probably won't get a chance to look at the board in closer detail until after the holidays are over, but at least now I have a wealth of potential troubleshooting techniques to go through.

 

[fyndr]

I have an update on the motherboard issue I've been experiencing with my LC III. I've gone ahead and tried various suggestions with the following results:

1. I scrubbed the affected area of the motherboard near the sound chip, audio jack, and speaker connector with CRC QD electronic cleaner and cotton swabs. I didn't do a full isopropyl wash since I currently don't have a high enough % of it or a spare toothbrush to work with. The cleaning didn't seem to have any effect on the issue.

2. I tried flexing the area near the sound chip lightly while the machine was operating to see if it might have been due to a trace issue. The speaker didn't respond one way or the other to this.

3. I removed the power supply and took my digital multimeter to it following the instructions provided by Elfen. The voltage readings I got were unusual to say the least. The +5V contact read a consistent 10.4V, the +12V at 25.0V, and the -5V at 0.0V. This seemed to be the case when double- and triple-checking the readings. I tried putting it back into the LC III and connecting to the motherboard, but then all the contacts read 0.0V. Removing the power supply again and all the leads read 0.0V, so I may have something wrong with the DMM itself. I checked the fuse inside of it and it appears to be intact (resistance reads ~0) so not sure what the problem could be.

I'll try checking the readings again tomorrow making sure to follow the AC voltage procedures exactly to see if there was an issue during measurement. Otherwise I may inspect the power supply board more closely to see if anything obvious is amiss.

 

[uniserver]

man yeah 25v on the 12v rail would be fireworks

 

[uniserver]

spray it down, (the mb) with Mr Sheen, i believe is what they call it there in au,  (active ingredient Silicone oil)

and bake it in the oven:

you should remove the pram battery… and clip.

ram and rom.
 
you could bake the main board in the oven @105C for 15 minutes…..
it worked great here, It worked good there for a while,  sometimes a good bake in the oven can get these things working again..
worst case scenario it will make it worse…. but realistically it will be the same or it will work again. 
 
so you place it into the oven… ( before you turn the oven on ) the preheat cycle will thermally shock it... but its fine,  close the door
 
set it for 105c and….
 
leave it alone… let it bake for 15 minutes…. 
then turn the oven off
 
open the door.. ( don’t touch it or bump it )  let it cool for another 10- 15 minutes and try it.
 
i bet it works.
 
 
 
also looks like ebay au they have what looks like a decent meter for a good price
http://www.ebay.com.au/itm/EXCEL-Digital-Multimeter-XL830L-Volt-Meter-Ammeter-Ohmmeter-Tester-Yellow-JNEG-/311199283023?hash=item4874ec374f:g:xxYAAOSw7hRWOwiT
 
here is a fellow Australian doing some multimeter reviews

 

[fyndr]

Thanks for the information, although I'm not Australian and not sure how that came about 

I checked my multimeter and it turned out I had it set to measure AC instead of DC. When I double-checked everything and looked at voltage on the rails, the readings were far more sane. +5V read a solid 5.07V, the +12V between 11.96V and 11.97V, and the -5V at -5.07V. I measured this with the PSU feeding power into the motherboard and checked at various times as the speaker popped, but didn't see any corresponding differences in the readings which might otherwise indicate this being the issue.

Before I bake the motherboard in the oven, I want to confirm the specific steps so I can make absolutely certain that I won't damage the board. From what you describe it'd be something like this:

1. Remove PRAM battery/clip and RAM stick from motherboard (as far as I know these are the only things that can be removed from the LC III motherboard apart from sundry plugs/cables connecting to other parts)

2. Spray motherboard with silicone oil (basically WD-40 from what I understand - if I don't have any on hand is it still OK to bake?)

3. Place motherboard in oven (on a cookie sheet or aluminum foil I assume)

4. Set oven to 105 degrees Celsius (~220 Fahrenheit)

5. After 15 minutes, turn off oven and open door. Allow 15 minutes to cool.

6. Put board back into LC III and boot it up

Is that about right, or am I missing any important details?

 

[uniserver]

not sure what the formula of wd40 is... but if you are in the US, PLEDGE, you can use. 

Pretty much correct, when you go to turn the oven off, don't touch or bump the pcb, until after it cools.

Electric ovens are ideal as they have the preheat cycle, That i'm pretty convinced gives the best results

btw where are you?

 

[Elfen]

DO NOT BAKE WITH WD40!

WD40 contains petroleum distillates (ie: Mineral Spirits) which will cause fire and corrosion to the board when heated.

You want Silicone oil.

Personally I never heard of it until I had Uniserver repair a Mac IIci board of mine and he sprayed it with Silicone oil. From the looks of it, it looks promising in that it is protecting the board... NYC air can be caustic to electronics since we got the pollution and the humid sea air at the same time all year long.

 

[fyndr]

Uniserver: I live in the US so I guess Pledge it is. I don't have any right now and I assume something like Lysol wipes wouldn't work quite the same way, so I'll pick up a can when I next have the chance.

Elfen: Yeah thinking about it putting WD-40 in the oven couldn't possibly end well. I have a can of silicone lubricant but it's basically the same thing and is extremely flammable.