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Another Mac SE/30 SCSI Problem
Posted by: Westinghouse on 2014-11-20 19:09:43 Hi there. This is my first post on this board, but I've already used the information in threads here to narrow down my problem. I recently picked up an SE/30 from a local shop, super cheap ($25). It boots from floppy just fine. It will boot from its hard disk into System 7.5.X and load all of the extensions, but immediately hangs at the desktop when loading the Finder, and the hard disk doesn't show up on the desktop. It will throw various errors when it hangs, sometimes a bus error, sometimes error 10. The hard drive also does not mount when booting from floppy. It won't show up for Apple HD SC, but it will show up for Disk First Aid's first menu... but no luck after that. Using a sketch from this forum, I checked the continuity between pins on the SCSI chip, and their corresponding pins on other chips and connectors. Everything came out OK except for the DRQ pin (third from the cut corner on the chip - see attached sketch, I indicated the pin in red). I get nothing between that pin and the corresponding pins on the Glue Logic Chip UI8 or on UK11. I started to run the traces backwards from the UI8 and UK11 pins. They both have a connection to a particular point on the board (see board image - point indicated in red). The image is not my logic board, but the layout is the same. I show no continuity between this point and the DRQ pin. I can't really follow the trace properly from this point back towards the SCSI chip, as it goes underneath the logic board power connector. I'm wondering if putting in a bridge from the DRQ pin to this connection point will get me SCSI back. I don't want to make a connection that will cause any further damage, though. Any advice?
Posted by: uniserver on 2014-11-20 19:23:54 gosh i hate to be the one to mention the elephant in the room, but... Umm... before you did all this. Did you change all the capacitors?
Posted by: uniserver on 2014-11-20 19:25:35 i think your bridge wire is always worth a shot.
Posted by: Westinghouse on 2014-11-20 19:35:57 Nope, haven't changed the caps yet. I know it's an issue because it doesn't bong on boot, and sound is really quiet from the speaker jack. I'm not really confident in my ability to do so... I'm somewhat inexperienced, especialy with regards to desoldering on circuit boards, and afraid of lifting pads. Does the DRQ line go through a capacitor? The lead seems to go very close to the board power connector, adjacent to a cluster of caps.
Posted by: uniserver on 2014-11-20 19:39:11 I think before you beat it up any more you need to do something about those caps. The are absolutely toasted. bad caps can give you all kinds of freeky stuff man. Bus errors, dead scsi, all that wild stuff.
Posted by: uniserver on 2014-11-20 20:20:40 pretty sure drq goes right to the GLUE
Posted by: uniserver on 2014-11-20 20:24:05 P51 Glue to P9 SCSI I/C
Posted by: uniserver on 2014-11-20 20:36:21 https://68kmla.org/forums/index.php?/topic/24102-se30-scsi-swim-glue-ic-pin-numbers/ /monthly_11_2014/post-1852-0-50179900-1416290893.png">View attachment 4744
Posted by: Westinghouse on 2014-11-21 17:16:45 Well, I ran a bridge over from the SCSI chip to the point I indicated on the board - success! It boots right up now. Thanks for the advice, and thanks to the forum - reading the threads on here about similar problems made it possible for me to do this repair myself. Next step is replacing caps!
Posted by: macalle69 on 2020-01-30 14:35:35 Hello Folks recently recapped a Macintosh SE30 , even if the computer booted ( with no sound due to bad capacitors) it did not recognize neither SCSI internal hard drive nor external scsi hd connected to the scsi port. After recapp at start up sounded strongly but the problem at SCSI still persist . I tested continuity from SCSI controller 53c80 to Glue and SCSI 50 pin connector and found no continuity : p6 scsi controller53c30 to p32 scsi connector p33 scsi controller 53c80 to p38 scsi connector I reconnected pins with wire .. and TA DAAA yep ! it's back to life again !
Posted by: trag on 2020-01-30 15:17:15 p6 scsi controller53c30 to p32 scsi connector p33 scsi controller 53c80 to p38 scsi connector I reconnected pins with wire .. and TA DAAA yep ! it's back to life again ! Excellent work. Way to track down the problem.
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