Hello, this is my first post here after years of lurking around. I ended up registering because I’d need some help with my Macintosh SE. Sorry if this post doesn't belong here.
After not using it since January, I started playing around with it the other day, and suddenly, when using it, it made an ugly noise (that came from the speaker), and since then, there’s no audio coming out of it. Neither from the speaker nor the headphone jack on the back. Also, the computer now shows a checkerboard pattern for some 10 seconds (check image) before booting up normally. The computer is usable, but there is no sound whatsoever.
I looked around the web for some schematics and run into the Bomarc ones. I used this one to check the audio path, from the BBU to the sound chip, and to the speaker. The traces seem okay, there’s continuity where there should be.
Seeing the schematics, I see the sound chip is also responsible with the RESET signal to the CPU, and there are capacitors around (C37, C32, C36 and C34). I thought, maybe any of these could have gone bad and it’s causing some issue, so I replaced them all (and I took good care of using a 1uF cap for C36). No luck. I kept the old caps, just in case, though.
I don’t have (easy) access to an oscilloscope, so I started measuring with the multimeter, and this is what I found:
1) All voltages seem pretty spot on, so I don’t think there’s any power supply issue.
2) The RESET output (pin 5), takes like 10 seconds to go from 0 to 5 V. This may be the cause of the checkerboard pattern, I think?
3) The Audio input (pin 16, which is coming from the BBU chip) starts off at 5 V, and then goes to around 1.8 V
4) The Audio output (pin 10, which goes through what I presume is a filter – C34, R6, C2) starts at around 12 V (although I’ve measured 14 V sometimes, then goes down), and stays there. The “presumed filter” works, and 0 V get to the speaker. No short seems to exist between +12 V and this pin, neither between pin 11, 12 or 13 and this pin (pin 10).
Now, I don’t have any other working (or non-working haha) Mac SE logic board around to check what should be normal or not. I think both points 3 and 4 are a bit suspect, but I’d need someone to tell me what their SE reads at those points.
Specially, number 2 and number 4 makes me think the chip has gone bad, so should I try to find a replacement? Can I replace it with something else? I know it's a reset line monitor (I'll call it that way), and it also filters PWM audio (I think? Please, correct me if I'm wrong).
Thanks in advance.
I'll leave some images for reference:
This is what the computer shows now before starting up normally
Sound chip, BBU and replaced caps
Bomarc schematics
After not using it since January, I started playing around with it the other day, and suddenly, when using it, it made an ugly noise (that came from the speaker), and since then, there’s no audio coming out of it. Neither from the speaker nor the headphone jack on the back. Also, the computer now shows a checkerboard pattern for some 10 seconds (check image) before booting up normally. The computer is usable, but there is no sound whatsoever.
I looked around the web for some schematics and run into the Bomarc ones. I used this one to check the audio path, from the BBU to the sound chip, and to the speaker. The traces seem okay, there’s continuity where there should be.
Seeing the schematics, I see the sound chip is also responsible with the RESET signal to the CPU, and there are capacitors around (C37, C32, C36 and C34). I thought, maybe any of these could have gone bad and it’s causing some issue, so I replaced them all (and I took good care of using a 1uF cap for C36). No luck. I kept the old caps, just in case, though.
I don’t have (easy) access to an oscilloscope, so I started measuring with the multimeter, and this is what I found:
1) All voltages seem pretty spot on, so I don’t think there’s any power supply issue.
2) The RESET output (pin 5), takes like 10 seconds to go from 0 to 5 V. This may be the cause of the checkerboard pattern, I think?
3) The Audio input (pin 16, which is coming from the BBU chip) starts off at 5 V, and then goes to around 1.8 V
4) The Audio output (pin 10, which goes through what I presume is a filter – C34, R6, C2) starts at around 12 V (although I’ve measured 14 V sometimes, then goes down), and stays there. The “presumed filter” works, and 0 V get to the speaker. No short seems to exist between +12 V and this pin, neither between pin 11, 12 or 13 and this pin (pin 10).
Now, I don’t have any other working (or non-working haha) Mac SE logic board around to check what should be normal or not. I think both points 3 and 4 are a bit suspect, but I’d need someone to tell me what their SE reads at those points.
Specially, number 2 and number 4 makes me think the chip has gone bad, so should I try to find a replacement? Can I replace it with something else? I know it's a reset line monitor (I'll call it that way), and it also filters PWM audio (I think? Please, correct me if I'm wrong).
Thanks in advance.
I'll leave some images for reference:
This is what the computer shows now before starting up normally
Sound chip, BBU and replaced caps
Bomarc schematics
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