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mobo for mac IIci
- Thread starter madmann
- Start date
tomlee59
Well-known member
Why not try fixing it? It could very well be something extremely simple. Here are some possibilities:
1) Bad jack: It's supposed to cut out the internal speaker(s) automatically when a plug is inserted. If the contacts get flaky, one or more channels might disappear on occasion.
2) Bad capacitor(s): As you noted, this could be a problem. Caps are cheap, so there's no harm in simply replacing 'em. Certainly replace any that are leaking/have leaked, and any that exhibit noticeable bulging at the top. The audio capacitors will generally be located near the speaker connector (although I don't know about the IIci for certain), and have relatively high capacitance values (e.g., 100uF or more).
3) Control panel setting: If the balance slider is set to one extreme, you'll only hear one channel.
This is hardly an exhaustive list, but it covers several common sources of the problem you're seeing. You can tell that the fixes are easy and inexpensive, so you may want to consider trying those first.
Others will shortly contribute their suggestions as well, I'm sure.
Good luck!
1) Bad jack: It's supposed to cut out the internal speaker(s) automatically when a plug is inserted. If the contacts get flaky, one or more channels might disappear on occasion.
2) Bad capacitor(s): As you noted, this could be a problem. Caps are cheap, so there's no harm in simply replacing 'em. Certainly replace any that are leaking/have leaked, and any that exhibit noticeable bulging at the top. The audio capacitors will generally be located near the speaker connector (although I don't know about the IIci for certain), and have relatively high capacitance values (e.g., 100uF or more).
3) Control panel setting: If the balance slider is set to one extreme, you'll only hear one channel.
This is hardly an exhaustive list, but it covers several common sources of the problem you're seeing. You can tell that the fixes are easy and inexpensive, so you may want to consider trying those first.
Others will shortly contribute their suggestions as well, I'm sure.
Good luck!
i pulled the mobo and inspected it. non of the caps look like they are leaking.
their is 0ne large blue electrolytic cap but it looks fine. the mobo has left speaker and right speaker printed on the board so i know there to look. there is one square film type cap and 4 small can type caps. it is these 4 caps that would concern me. they have the following printed on top of them
2s
47
16v
i am not sure what size they are
their is 0ne large blue electrolytic cap but it looks fine. the mobo has left speaker and right speaker printed on the board so i know there to look. there is one square film type cap and 4 small can type caps. it is these 4 caps that would concern me. they have the following printed on top of them
2s
47
16v
i am not sure what size they are
wally
Well-known member
As a guess based on only a few topside measurements on a scrap mobo, the sound comes out of UB2 and UB3 pin 11, goes to the + side of C2 and C3 which are 47 uF 16V aluminum SMT caps (could easily be faulty open or short), then proceeds out the - ends thru 180 ohms and possibly some underside EMI filtering to the switching stereo output jack, which as tomlee59 indicated could easily have an open contact.
So if you have an ohmmeter and a stereo patch cable, with power off see if you get 180 ohms from each external channel to the - side of C2 and C3 for the left and right channel outputs, and see if the + sides of C2 and C3 do connect to pin 11 of the two sound chips. With proper ohmmeter polarity directly across each electrolytic, both C2 and C3 should charge up to an open circuit (anything measuring greater than 10Kohms is fine).
If you have proper continuity, then you can try a power up test by carefully temporarily bridging C2 then C3 with an external blocking capacitor of similar value (and polarity!) in case one of these is open.
Alternatively you can patch headphones (or powered speakers) direct from ground to the - side of C2 and C3, and next if necessary use an external temporary headphone blocking capacitor of similar value and polarity connected direct to pin 11 to see if each sound chip is outputting appropriate sound voltages.
So if you have an ohmmeter and a stereo patch cable, with power off see if you get 180 ohms from each external channel to the - side of C2 and C3 for the left and right channel outputs, and see if the + sides of C2 and C3 do connect to pin 11 of the two sound chips. With proper ohmmeter polarity directly across each electrolytic, both C2 and C3 should charge up to an open circuit (anything measuring greater than 10Kohms is fine).
If you have proper continuity, then you can try a power up test by carefully temporarily bridging C2 then C3 with an external blocking capacitor of similar value (and polarity!) in case one of these is open.
Alternatively you can patch headphones (or powered speakers) direct from ground to the - side of C2 and C3, and next if necessary use an external temporary headphone blocking capacitor of similar value and polarity connected direct to pin 11 to see if each sound chip is outputting appropriate sound voltages.
