68kMLA Classic Interface

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Another "Ticking" Macintosh Plus ED

Posted by: uniserver on 2015-08-29 13:51:33 yeah get on those caps, sometimes they look great and the lead on the inside is completely burnt up… i'v seen that bunches of times now. i think its a bad resistor. the same thing happens with the focus pot.   if the resistor is bad turning the pot does nothing.

Posted by: uniserver on 2015-08-29 13:52:03

Posted by: Ferrix97 on 2015-08-31 03:43:48 If I power the machine with a Variac, I can get it to provide the correct voltages without ticking or going into protection, the voltage control trimmer lets me adjust (not by much) the output voltage. But there is no chime, video or sound. The logic board is good as I've tested it in the other Plus ED, and I am measuring the voltages from the floppy port, so they are definitely getting there.

Posted by: Ferrix97 on 2015-08-31 07:45:21 Actually, the mac chimes and boots (using an external speaker and hard drive). So this board has no audio and no video + unregulated power supply.... Great! At this point, I think I'll take a look at the video section (the flyback is new). As for the sound, I don't think there is much on the AB, the only thing that could fail is the speaker (I can steal one from a dead Mac Classic or a dead SE/30) EDIT: actually, maybe "no video" is caused by the fact that there is not enough voltage for the oscillator to start, so no voltage coming from out of the flyback EDIT 2: Yup!, I should have +30V on C14, but I only have about +5V

Posted by: Ferrix97 on 2015-08-31 08:51:40 The speaker tested fine, so I swapped the main logic board cable and... It also brought sound back! Now I can power the machine without the Variac and it chimes perfectly! At this point, I need to find new contact clips for the cable and them it's ready to go! Oh, and also get rid of those scan lines (they only appear when the brightness is all the way up)

Posted by: Ferrix97 on 2015-08-31 09:46:25 I cleaned and bent back pins in the connector, adjusted the cut-off and... Done! Now I only need to find some ROMs for it Again, out of all of the ABs I've repaired, I've never found one that needed new capacitors (I haven't fully recapped this yet, just swapped two caps)

Posted by: uniserver on 2015-08-31 13:53:06 you mean out of the five analog boards you have repaired...    lol.. what a guy....

Posted by: Ferrix97 on 2015-08-31 14:16:46 Yes!, But I've also seen (here in Italy) lots of listings for fully working machines. My Macintosh 128K works perfectly and it has never been repaired (still has the original double-sided sticky tape holding the vinyl cover to the AB). Maybe the International version of the board is slightly more rugged than the US model. On the other hand, I've never seen a Mac LC or SE/30 with good capacitors on its logic board.

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