tom@mhuxd.UUCP (GLINOS) (10/22/85)
About a month ago I completed the DDJ upgrade. Everything went well. A few days ago my mac quit. On power up the machine buzzes and displays 4 sad macs. The macs are located in the centre middle centre bottom. The two other macs are split at the edges of the screen and wrap around. The numbers under the sad mac vary but are either 04FFF8 or 020000 (or some variation). Anybody have any ideas?
callen@ada-uts.UUCP (10/28/85)
> About a month ago I completed the DDJ upgrade. Everything went well. > A few days ago my mac quit. On power up the machine buzzes and > displays 4 sad macs. The macs are located in the centre middle > centre bottom. The two other macs are split at the edges of the > screen and wrap around. The numbers under the sad mac vary but > are either 04FFF8 or 020000 (or some variation). > Anybody have any ideas? I've done a half dozen DDJ upgrades and never seen THAT specific problem, but I've had to shoot OTHER problems. They have (so far) ALL been caused shorts between pins in the memory array (no comments about sloppy soldering, please). Run the continuity tests listed in the DDJ article, and check for shorts. Unfortunately, if you find a short and it involves only the "common" lines in the array (which is nearly all of them), you may have to pull ALL of those nice new sockets to find it (someone PLEASE tell me that there is a better way...). Pull the sockets one at time and re-test. So far I've been lucky - one short involved pin 14 (which nailed it to a single chip), and the other was the second socket I pulled off the board. The DDJ upgrade is nice and cheap, but it's not for the fearful or the novice soldering hacker... Jerry Callen ...ihnp4!inmet!ada-uts!callen
srb@ccvaxa.UUCP (11/08/85)
------------ ------------ Someone who had done a DDJ conversion was asking about how to fix shorts under a socket without removing the whole row. One aid is to use a high-precision ohmmeter (Fluke 4 1/2 digit multifunction meter works), i.e., one which will discern a milliohm or so. You can locate a short to within an inch or so on 10 mil traces like the Mac's. We used to do it all the time on some boards we made. The easiest way to fix open/short problems under a socket is to use sockets with "open entry" pins. After being soldered into the board, the plastic shells of such sockets can simply be pulled off the pins (gently!) with a pair of pliers, leaving all 16 pins sitting firmly soldered into the board. Then put the shell back on (gently!) after the problem is fixed. You can generally spot such sockets by simply turning them over and looking at their undersides. (To be really sure, grab a pin with a pair of pliers and try to pull it out. It should come out and go back in relatively easily.) It is non-trivial to solder a replacement pin into the PC board straight enough to align correctly with the shell, without the shell in place. Don't try. Just put the pin into the shell, re-insert the shell/pin, and resolder. I did the Levco upgrade, and when finished with both the removal and the socket-soldering steps, spent a half hour with a 8x (slide loupe) magnifier examining holes, traces, etc. Time well spent. Found a couple of potential bridges. The upgraded Mac worked first time. Steve Bunch. ..!uiucdcs!ccvaxa!srb ------------