brayne
Well-known member
Hi all, this is a duplicate of a post I published on a Mac group on Facebook, so my apologies if you're reading this for the second time.
I was hoping to get some help from one of the tech gurus out there regarding a Mac Classic II analog board (820-0525-B 240V).
The board wasn't working, so I started by replacing all of the leaky caps (specifically CP2, CP6, CP7, CP8, CP9, CP10, CP12 & CP36) and giving the board a good clean. When I powered it up, it immediately blew the fuse, so I replaced the QP2 MOSFET and the IP1 voltage regulator which solved that problem.
Now it fires up fine, I'm getting a nice, steady 5v and the Mac boots and operates normally. The only problem is that it occasionally restarts all by itself. There doesn't seem to be any consistency to it. Sometimes it restarts after just a few seconds, and other times it will work perfectly for an hour before restarting. It's a known-good logic board, so the problem is definitely on the analog board somewhere.
Larry Pina's book on Classic & SE repair and upgrade secrets suggests that this symptom is being caused by a cracked solder joint on the high voltage transformer ZP1. So I removed ZP1, cleaned all the pins and soldered it back on, but it doesn't seem to have made a difference.
Has anyone else encountered this issue before? Or can someone offer any suggestions on what might be causing these intermittent restarts? Apart from this, everything else about it seems to work perfectly.
Thanks in advance.
I was hoping to get some help from one of the tech gurus out there regarding a Mac Classic II analog board (820-0525-B 240V).
The board wasn't working, so I started by replacing all of the leaky caps (specifically CP2, CP6, CP7, CP8, CP9, CP10, CP12 & CP36) and giving the board a good clean. When I powered it up, it immediately blew the fuse, so I replaced the QP2 MOSFET and the IP1 voltage regulator which solved that problem.
Now it fires up fine, I'm getting a nice, steady 5v and the Mac boots and operates normally. The only problem is that it occasionally restarts all by itself. There doesn't seem to be any consistency to it. Sometimes it restarts after just a few seconds, and other times it will work perfectly for an hour before restarting. It's a known-good logic board, so the problem is definitely on the analog board somewhere.
Larry Pina's book on Classic & SE repair and upgrade secrets suggests that this symptom is being caused by a cracked solder joint on the high voltage transformer ZP1. So I removed ZP1, cleaned all the pins and soldered it back on, but it doesn't seem to have made a difference.
Has anyone else encountered this issue before? Or can someone offer any suggestions on what might be causing these intermittent restarts? Apart from this, everything else about it seems to work perfectly.
Thanks in advance.
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