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| Macintosh Classic Analog Board Help |
Posted by: embBambooLounge on 2023-05-07 19:08:57
My Dad pulled our original Macintosh Classic out of a closet and gave it to me last week. We thought it was sold at a yard sale but it turns out we still had it. After giving it a once over the logic board had some capacitor leakage but no real damage. The analog board was a mess with capacitor leakage. I pulled the caps, cleaned the board with IPA and a lot of Q-Tips but didn't completely wash it with warm soapy water or anything. I pulled all the caps and replaced them all with a kit from Console5 on both the analog board and logic board. I plugged everything in and fired it up and it sounded like the power supply was struggling to start and high voltage didn't quite kick in. As I went to check the voltages on the floppy connector the capacitor in CP2 started to blow it's guts out the top and the C8 capacitor on the logic board started to brown (replaced logic board caps with tantalums). Yes, I know I shouldn't have had the logic board plugged in.. I was over confident. Anyway, I have read on here that some other common components that have issues are "TDA4605, CNY17G, IRFBC40, DP3 and DP4 (1N4148)." so I've ordered those. I am not finding nearly as much troubleshooting info on the Classic as I did for my SE and Macintosh Plus with Larry Pina's book so any leads to follow would be appreciated. |
Posted by: dochilli on 2023-05-08 00:56:58
Mac Classic & SE from Larry Pina could help you. Perhaps you send me a PM? |
Posted by: Phipli on 2023-05-08 01:13:34
My Dad pulled our original Macintosh Classic out of a closet and gave it to me last week. We thought it was sold at a yard sale but it turns out we still had it. After giving it a once over the logic board had some capacitor leakage but no real damage. The analog board was a mess with capacitor leakage. I pulled the caps, cleaned the board with IPA and a lot of Q-Tips but didn't completely wash it with warm soapy water or anything. I pulled all the caps and replaced them all with a kit from Console5 on both the analog board and logic board. I plugged everything in and fired it up and it sounded like the power supply was struggling to start and high voltage didn't quite kick in. As I went to check the voltages on the floppy connector the capacitor in CP2 started to blow it's guts out the top and the C8 capacitor on the logic board started to brown (replaced logic board caps with tantalums). Yes, I know I shouldn't have had the logic board plugged in.. I was over confident. Anyway, I have read on here that some other common components that have issues are "TDA4605, CNY17G, IRFBC40, DP3 and DP4 (1N4148)." so I've ordered those. I am not finding nearly as much troubleshooting info on the Classic as I did for my SE and Macintosh Plus with Larry Pina's book so any leads to follow would be appreciated. Do you have a photo of the boards? |
Posted by: embBambooLounge on 2023-05-08 05:07:35
Do you have a photo of the boards?
Absolutely! Thank you for looking! |
Posted by: imactheknife on 2023-05-08 05:14:09
i think caps are backwards on logic board.. red stripe faces positive.. |
Posted by: cheesestraws on 2023-05-08 05:19:26
i think caps are backwards on logic board.. red stripe faces positive..
Yeah, does look like that.
@embBambooLounge - the stripe on tantalum capacitors, confusingly, denotes the other end than it does on aluminium can capacitors. Yes, this is silly and inconsistent, but it's ... what is. I think you might have lined the stripes up, so all your tantalums are on backwards, which will make them extremely unhappy in a potentially firey way. |
Posted by: Phipli on 2023-05-08 05:47:15
Yup, looks like the caps are backwards, although the picture is very low resolution - for checking board faults you need high resolution, well lit photos without bright reflections, so that it is possible to see the details. |
Posted by: joshc on 2023-05-08 05:48:39
Yup, your tantalums are on backwards so that would've been causing the problems you were seeing. I can see the one that went brown, it was obviously overheating and would've probably expldoed had you left the machine switched on for any longer. |
Posted by: embBambooLounge on 2023-05-08 07:29:42
Wow, this is incredibly embarrassing .. I am beside myself. I have never swapped out for tantalum caps before and boy oh boy am I embarrassed. Would this reverberate back into the analog board and cause C2 on the analog board to go sideways as well? Thank you for your help - I actually have a bunch of surface mount caps that I could have used for this board but bought the tantalums on a whim. Yikes. I will replace them tonight and report back. I've included better pictures - my last export was on medium settings by accident. If you see anything else horribly wrong please let me know. Thank you all again .. live and learn! |
Posted by: cheesestraws on 2023-05-08 07:41:04
Wow, this is incredibly embarrassing .. I am beside myself. I have never swapped out for tantalum caps before and boy oh boy am I embarrassed
I expect everyone in this thread has put at least one tantalum in backwards at some point or other. I have. It's easy to do, and it's just one of those things that happens unless one is one of nature's obssessives. No need to be embarrassed, you're in good and large company...
Would this reverberate back into the analog board and cause C2 on the analog board to go sideways as well?
CP2? The P I think means 'power' and is part of the power supply: given that you just gave the PSU an impromptu stress test, it might have, but it probably shouldn't have.
I'd suggest checking that all your other capacitors are in the right way around too, just for your peace of mind if nothing else. |
Posted by: imactheknife on 2023-05-08 19:49:57
Wow, this is incredibly embarrassing .. I am beside myself. I have never swapped out for tantalum caps before and boy oh boy am I embarrassed. Would this reverberate back into the analog board and cause C2 on the analog board to go sideways as well? Thank you for your help - I actually have a bunch of surface mount caps that I could have used for this board but bought the tantalums on a whim. Yikes. I will replace them tonight and report back. I've included better pictures - my last export was on medium settings by accident. If you see anything else horribly wrong please let me know. Thank you all again .. live and learn! Yup, very easy to do! I check and recheck but can still make that little mistake.. no harm done thankfully!! Keep up posted🙂 |
Posted by: embBambooLounge on 2023-05-09 11:44:01
Last night I went over the analog board looking for reversed capacitors and I found another one in the crowded area of the board where the + marking wasn't as straight forward so I fixed that and replaced the one that went bad. Now when I power up the analog board (without the logic board) I'm not getting the "flupping" of a board in distress and the voltages are stable. They're a little on the low side at the moment but I didn't want to adjust it until the logic board was drawing power. I didn't have the exact right cap to replace the burned one like I thought I did so I ordered replacements and they should be here today. Thank you everyone for your help! I will keep you all updated! |
Posted by: imactheknife on 2023-05-09 17:24:15
Last night I went over the analog board looking for reversed capacitors and I found another one in the crowded area of the board where the + marking wasn't as straight forward so I fixed that and replaced the one that went bad. Now when I power up the analog board (without the logic board) I'm not getting the "flupping" of a board in distress and the voltages are stable. They're a little on the low side at the moment but I didn't want to adjust it until the logic board was drawing power. I didn't have the exact right cap to replace the burned one like I thought I did so I ordered replacements and they should be here today. Thank you everyone for your help! I will keep you all updated! I think you have to have hard drive plugged in and logic plugged in when you power on to get stable voltage. Dont think it’s a good idea to power on with no draw on power etc, but could be wrong on that. Cheers, mark |
Posted by: embBambooLounge on 2023-05-12 08:35:43
Thank you to everyone that helped me out with this project. I got the capacitors and replaced on the logic board AND with the correct polarity and it booted up! I can't believe it! Even the old hard drive spun up and it loaded system 6! I am so excited! The RAM expansion board worked as well and it has 4MB as well. What's the max this can handle? Anyway, now back to trying to figure out what the heck is wrong with the Mac Plus I picked up! 😊🤔 |
Posted by: cheesestraws on 2023-05-12 10:10:30
Well done! Good stuff. Nice to see it working 🙂
4MB is the most you'll get in a Classic, it's very similar to an SE. |
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