68kMLA Classic Interface

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I did a bad bad thing!

Posted by: mattpnew on 2016-01-03 21:03:35 Hi Guys, Was busy cosmetically restoring a 128k Mac (US) and stupidly plugged it in, it went pop and tripped the home circuit breaker. Obviously the fuse will need replacing, what other damage have I done to this poor little guy! Thanks in advance, Matt

Posted by: Elfen on 2016-01-03 21:26:22 What was plugged in? The CRT? The Logic Board? Floppy Drive? Anything on the analog board popped/fried/smoked? Without details, it's hard to say. And by "Cosmetically Restoring", what were you doing? Send pictures...

Posted by: CC_333 on 2016-01-03 22:04:18 Well, if you're in Europe somewhere, then I would suppose you fried something on the analog board (because the US A/B is not designed for 50Hz 220V), which, if you're lucky, can be replaced fairly easily. c

Posted by: mattpnew on 2016-01-03 23:19:09 Just a good clean, then removing any yellowing.

Posted by: mattpnew on 2016-01-03 23:20:29 There was no smoke or smell, just a pop, the home safety switch kicked in pretty quick. I can see the fuse is stuffed but no other visible damage.

Posted by: uniserver on 2016-01-03 23:34:34 if you plugged in a 120v mac into 240,  the ab is toast.

Posted by: mattpnew on 2016-01-03 23:43:10 I have an ab board out of a mac plus (AU Model) floating around, is it as simple as swapping it over?

Posted by: uniserver on 2016-01-04 00:30:25 Yes you can swap that out,  The originality people might not like that if you go to sell it... but yes it will work.

Posted by: mattpnew on 2016-01-04 00:36:27 Will try and get it fixed / find a replacement if one becomes available.

Posted by: Paralel on 2016-01-04 02:40:30 Yeah, Uni is right, damage was likely contained to the analog board. You analog board committed honorable suicides in this case of catastrophic failure to spare the rest of your machine. Give it a warrior's burial.

Posted by: CelGen on 2016-01-04 03:59:00 You've blown the bridge rectifier or the initial components of the primary PSU stage which for the most part is repairable but you might of also just blown the primary transformer, in which case it's game over and you got yourself a nice paperweight until you find a replacement and suitable analog board.

Posted by: mattpnew on 2016-01-07 05:42:21 Thanks for all your advice, here are some pics... the only obvious damage seems to be between the R44 and R50. Is there a easy way to diagnose or who these days can do the repair if possible or simply give up and try to source a new board?

Posted by: Paralel on 2016-01-07 05:50:01 Talk to Uniserver, he has brought boards back from the dead that you wouldn't think possible. Also, I'd say, at a minimum, your R48 & R45 are blown to smithereens. Those two look like they took out R44, R47, & R49 in the process. Anything before R45 is probably gone, and anything in between R45 & R48 is probably also gone. Its hard to say how far beyond R48 the damage goes.

Posted by: Elfen on 2016-01-07 10:07:53 If the transformer is OK, then this should be easily fixable. But that's a big If. Best to get a back up board in the meantime. Tried ebay?

Posted by: techknight on 2016-01-09 15:30:59 Since I see transistors blown apart, the whole primary section has to be rebuilt. I used to service electronics for years with damage more extensive than this.  All transistors, including the burned resistors have to be replaced in the primary side. Other resistors and diodes have to be checked for opens and shorts, and replaced as well. the Opto-isolator will likely need replaced.

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