68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.

Early 128k 512k analog board(s) repair

Posted by: avadondragon on 2015-10-27 21:26:17 I recently came into possession of a 512k Mac. I was really excited because it has the RAM upgrade and a SCSI controller card soldered straight to the CPU!  But it also has a very fried analog board.  Specifically the transistor Q3 is burned to a crisp, CR1 and R14 got hot enough to discolor the PCB.  I'm attaching pictures.  This doesn't sound like any type of failure I've read about so I was wondering if anyone had any advice to give. I also have an even earlier analog board that I think came out of a 128k or very early 512k Mac.  It looks like it has a burned up flyback transformer.  I know those are becoming very rare these days.  Maybe I could pull the flyback off the other board and see if it works? I would like to repair one or both of these boards but I wanted to see if anyone had any input before I ordered the parts sitting in my DigiKey shopping cart.

Posted by: avadondragon on 2015-10-27 21:30:07 Pics of the older analog board:

Posted by: Macdrone on 2015-10-27 22:04:48 At this point trade all the good parts to the board with the least damage.  Its a great start.

Posted by: trag on 2015-10-28 02:17:13 Dalbani on EBay or from their store, still has stock of the 157-0026 fly back, but their price is around $25 - $30 now. Still, if it's the only way to get a 'new' one... I think Artmix sells flashbacks as well. It looks like he paid to have a new production run made. I don't remember his pricing on them.

Posted by: Apache Thunder on 2015-10-28 09:15:40 I'm seeing the entire analog board on eBay for slightly more then that. Better to just pick that up instead. There's only one listing for it though, so you better hurry. 😛 The rest are way overpriced and you can find entire units for the prices they have for them. 😛

Posted by: avadondragon on 2015-10-28 12:33:12 I looked on eBay too and concluded that I could buy another analog board or even pick up an entire Mac Plus nearly as cheaply as I could repair these.   The problem with that is ALL of these analog boards are almost 30 years old and starting to fail.  Even if I buy another it may fail in the next year or two.  I just feel like it is better to repair than replace if I can manage it. I found a source for the 157-0042B at $25 The flyback from an SE is compatible right?

Posted by: CC_333 on 2015-10-30 15:35:50 All flybacks from the 128k throught the SE/30 are interchangeable. I'm not sure about the Classic/Classic II (I think so). Later ones (like from an SE or SE/30) are better, because they are heavier duty than the early ones, and thus less prone to failure due to overheating. c

Posted by: unity on 2015-10-30 17:26:30 Maybe I need to pull and stockpile these. I have 3 SE/40 boards for parts and many, many other Plus/SE boards. But I agree, new would be best.

Posted by: avadondragon on 2015-12-19 20:00:00 The reworks were a success!  My 512k is now fully operational!  I misplaced my 2nd flyback though so I only managed to finish one of the two analog boards.  Also managed to repair an old 1xx series PowerBook power brick at the same time.  Feeling super accomplished.  Next up: Centris 610 recap.

Posted by: uniserver on 2015-12-19 23:40:22 nice bright crt picture   good job!

Posted by: bibilit on 2015-12-20 02:52:23 Nice job, picture is a bit slanted, don't remember but think rotating the little magnets can solve this issue.

1