68kMLA Classic Interface

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LC475 6R8 resistor blew

Posted by: vilasaliv on 2016-11-26 14:19:26 As soon as I got my lc 475 running (It was 6y in a closet) I smelled burned fuse, heard some white noise for 5 sec and after that no sound from the speaker. The mac started up well besides that. Later I checked the sound was ok on the audio out but the speaker was silent all the time. The speaker works with a spare main board. I looked to the board and it has a resistor broke. A 6R8 resistor near the year of the board and the audio out (see picture). Is that resister the responsible for the non audio on internal speaker? Do you think a new one won't blow again? should I check something before I replace it? Do you know some similar experience and how was it solved? Thanks, SV, Portugal.

Posted by: just.in.time on 2016-11-29 20:29:03 I haven't had an LC 475 before, but my guess would be probably. If I were in your shoes I'd try picking up a few of those resisters online. If the board hasn't been recapped yet, now would be a good time to remove the caps, wash the board, and put new caps on. Put a new R68 resister in place. This will probably solve your problem (assuming no traces are eaten through) If the board is already recapped, then just remove the old resister and put the new resister on. In either case, hopefully it works after that. If it doesn't, you will need the diagram to figure out where that R68 is in line and begin hunting.

Posted by: techknight on 2016-12-15 14:09:07 Was it working on BOTH channels on the audio-out jack? If so, that would indicate U32 is likely bad which blew the resistor. The other possibility is C161 developed a short, it is a tantalum capacitor and they are known for that when they age.  Oh, and dont forget to recap that board. likely leaky and shot.

Posted by: vilasaliv on 2019-03-17 04:55:38 I'm listing this board with the 68040 motorola processor on ebay. http://ebay.us/fclLTc?cmpnId=5338273189

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