68kMLA Classic Interface

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My New Classic II

Posted by: jmasterfunk on 2021-07-23 14:46:50 After years of waiting, I finally came across Compact Mac that wouldn't break the bank for me. First one. Unfortunately, it isn't working. I get an extremely dim vertical line pattern. These lines are not visible with the naked eye with the light on. The exposure on this image is cranked right up. I have re-capped the logic board, and the same line pattern remains. I haven't been able to find any other postings with this exact fault. No sounds. I would assume this is an issue with the logic board not providing brightness, and of course providing a useless image. I'll start to slowly poke around for signals, however, any head start would be appreciated.

Posted by: mg.man on 2021-07-23 14:56:56 You should be able to crank up the brightness using the potentiometer on the analog / power board. I also suspect the "narrow" display can be 'widened' using another [horizontal width] potentiometer on the analog board. Re-capping the analog board should be on your list. Have you pulled the ROM chips and checked they are clean?

Posted by: LaPorta on 2021-07-23 14:57:41 With the screen not bright at all, and what appears to also be a compressed picture horizontally, I would think possibly low voltage issues with the analog board. Has it been recapped?

Posted by: jmasterfunk on 2021-07-23 15:00:44 Interesting. I'll try the width adjustment. Analog board not yet re-capped. Wanted to do the logic board first, and was hoping that I would get something different on the screen after the logic board re-capping.

Posted by: mg.man on 2021-07-23 15:05:17 Pull the ROMs and check the pins are clean. Also make sure they are in the correct sockets and that they are positioned correctly in the socket. Need to check, but some of the Classic 'boards have ROM sockets that have more pins than the actual ROM chips.

Posted by: mg.man on 2021-07-23 15:05:50 Post a picture of your logic board.

Posted by: joshc on 2021-07-23 15:18:39 These analog boards need recapping. Apple put a cluster of capacitors right next to a transformer, they get hot and dry out and leak heavily all over the board, often corroding the copper on the other side. You can measure the voltages you are getting using this trick with the rear floppy port: With your multimeter, use the pins above to check 12V and 5V. Please post photos of your logic board and analog board.

Posted by: jmasterfunk on 2021-07-23 15:34:57 Voltages are good. -12, +12, 5. However, seems there must be a bad solder joint on the logic board. Pulled it out of the chassis slightly, pulled out the SCSI and floppy cables. This flexed the board up. Attempted a power up, and it was successful. Inserted board fully into chassis. boot up okay again. Inserted SCSI, no boot. Flexed the board up, and we had boot yet again. Time for the toaster oven, I guess.

Posted by: jmasterfunk on 2021-07-23 15:35:50 Glamour shot of the logic board.

Posted by: 4seasonphoto on 2021-07-23 21:01:58 Power supply may still be weak despite seemingly okay voltage readings, and the fact that the screen is dim and that the system seems to work better when you unplug current-hungry devices like SCSI and floppy drives is "interesting".

Posted by: joshc on 2021-07-24 01:04:59 @jmasterfunk Have you got a high res version of that photo? It's really tiny (for me at least) so I can't see anything on it. I wouldn't expect the machine to work very well unless the analog board is recapped really - you mentioned stable voltages but they might not be stable under further load (i.e. when SCSI is in use, when the machine is actually trying to do anything). Has the board been cleaned?

Posted by: jmasterfunk on 2021-07-29 12:01:09 Sorry about that. Here's the better version. It's been cleaned with 99% isopropyl. Have not gotten around to attempting to reflow yet. Will make plans to recap the analog.

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