68kMLA Classic Interface
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| Macintosh Plus issues with analogue board | |
| Posted by: Maccollector on 2025-12-13 02:42:26 I have recently obtained Macintosh plus in a poor state . After cleaning corrosion from the analogue board , board ran fine but now it seems to be power cycling when it get hot, Some diodes are getting very hot and resistors. Are these meant to get hot or not. I have some thermal images and normal images . Here are the pictures of components getting hot. Also there is a video of what mac is doing I read somewhere this issue with the voltages but unsure as to how to fix them | |
| Posted by: Maccollector on 2025-12-13 02:47:08 Also I am trying to upload a 7 sec vid will this link work | |
| Posted by: bibilit on 2025-12-13 03:05:20 I will check voltages, you are getting a clear chime, so not bad, most AB are dead and not delivering any. Can be a bad solder joint, don’t see any hot spot either. But those two RIFA caps should go. | |
Posted by: Maccollector on 2025-12-13 03:07:38I will check voltages, you are getting a clear chime, so not bad, most AB are dead and not delivering any.So those thermal images do not seem out of ordinary .. Only asking as I don't know what is getting hot. If a leave it off for a while it will boot and stay at floppy drive with question mark logo for few minutes before starts power cycling Where and how to check voltage if you can tell me please | |
| Posted by: Maccollector on 2025-12-13 04:35:33 And for the record, 5v rail at floppy connector sits @ 4.5 but does not fluctuate during power cycle. 12v rail sits @12.01 at wholes 7 & 8 | |
| Posted by: bibilit on 2025-12-13 06:21:29 5 volt rail is a bit low…try to crank it up to 4,8 There is a potentiometer on the side of the AB. Try reflowing the solder joints at the usual places. | |
Posted by: Maccollector on 2025-12-13 20:34:245 volt rail is a bit low…try to crank it up to 4,8I did adjust it and it seems stable I did it without proper tools.. and it goes like this. Turn the screw, start the mac, check voltage . One thing is that my 12v rails now sits at 12,7. Does this point out to capacitor issue? | |
| Posted by: Byrd on 2025-12-13 21:38:19 Give the analogue board a tap at startup, I think you've some good old dry solder joints here too. Yes, replacing the capacitors will help you here - notably the low voltage big ones (eg. the 1 x 16V 4700uF and 4 x 16V 2200uF I think it is). | |
Posted by: Maccollector on 2025-12-14 00:16:35Give the analogue board a tap at startup, I think you've some good old dry solder joints here too. Yes, replacing the capacitors will help you here - notably the low voltage big ones (eg. the 1 x 16V 4700uF and 4 x 16V 2200uF I think it is).I am ordering all electrolytic capacitors, but was curios ( i did not check) what are riffa capacitors values; This is 240v board | |
| Posted by: Byrd on 2025-12-14 00:38:49 Earlier boards have a huge sized 0.47uF X2 RIFA capacitor, later boards have 2 x 4700pF X2 capacitor (much smaller), both rated 250V or higher. I'm restoring several Mac Pluses at the moment and yet to find a dud 200V 100uF capacitor (the four big ones usually purple colour. There is also a large 35V 3.9uF yet to touch (and hard to source much near the same uF). | |
Posted by: Maccollector on 2025-12-14 13:54:26Earlier boards have a huge sized 0.47uF X2 RIFA capacitor, later boards have 2 x 4700pF X2 capacitor (much smaller), both rated 250V or higher. I'm restoring several Mac Pluses at the moment and yet to find a dud 200V 100uF capacitor (the four big ones usually purple colour. There is also a large 35V 3.9uF yet to touch (and hard to source much near the same uF).I have some Y2 riffa caps. Will they be sufficient enough considering this machine will be turned on periodically | |
| Posted by: luRaichu on 2025-12-14 14:06:45 Blackened leg on diode looks bad. See "Dead Mac Scrolls" about replacing it | |
Posted by: Maccollector on 2025-12-14 18:33:47Blackened leg on diode looks bad. See "Dead Mac Scrolls" about replacing itAre you talking about CR1 diode above flyback converter? | |
Posted by: luRaichu on 2025-12-14 19:25:11Are you talking about CR1 diode above flyback converter?Yes. Actually the diodes aren't mentioned in "The Dead Mac Scrolls" but rather the earlier "Macintosh Repair & Upgrade Secrets" 
Macintosh Repair & Upgrade Secrets 1990 : Free Download, Borrow, and Streaming : Internet ArchiveMacintosh Repair & Upgrade Secrets 1990
archive.org
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Posted by: Maccollector on 2025-12-14 19:53:21Yes. Actually the diodes aren't mentioned in "The Dead Mac Scrolls" but rather the earlier "Macintosh Repair & Upgrade Secrets"Research suggests it is a 100v 1A diode but my board is 240v does that matter? | |
| Posted by: luRaichu on 2025-12-14 20:11:16 CR1 is in the flyback circuit, so mains voltage doesn't matter. The book says 3A diodes were originally used, they should be replaced with at least 5A rated diodes. | |
Posted by: Maccollector on 2025-12-14 20:31:51CR1 is in the flyback circuit, so mains voltage doesn't matter.Voltage? | |
| Posted by: Maccollector on 2025-12-14 20:37:17 will this one do the job | |
Posted by: luRaichu on 2025-12-15 06:45:40Voltage?Book says replace with at least 35V rating. The ones you picked will do the job | |
Posted by: s_pupp on 2025-12-15 07:11:04I have some Y2 riffa caps. Will they be sufficient enough considering this machine will be turned on periodicallyX2 and Y2 caps are not interchangeable. | |
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