WIRING HARNESS SOLUTION by John Alwood, RKUG, July 1987 (A look at a wiring harness problem in early Kaypros) THE PROBLEM: You are sitting at your computer and you notice that any of the following events happen at irregular intervals: (1) one disk drive starts up under its own initiative -- without the benefit of control from the program you may be using at the time; (2) both disk drives light up, but they may not actually begin moving (ie, rotating and moving the read heads) and they may actually "lock up" and force you to re-boot before you can save anything; and/or (3) your entire system locks up and you must reboot to regain control. In the later stages of the problem, even a "reboot" won't solve the problem. Sometimes, powering the computer off and on will work. Eventually, the machine will not work at all. The problem may seem heat-related because it usually only happens after the computer has been running for awhile. THE DIAGNOSIS: The problem is heat-related. It is also "vibration" related. And, most of all, it is "solder" related. One of the solder joints on the power supply board connecting the wiring harness to the board has"expanded" and has caused the pin to lose contact with the power supply board (there are about 9 or 10 pins in this wiring harness). As a result, your computer loses its power source -- either the A/C voltage from the power line is not making it into the power supply circuits, or the DC voltage from the power supply board is not making it over to the main CPU board and disk drives. Due to the "heat" expansion at the location of the defective solder joint, your computer effectively loses power and "locks up". Vibrations (such as banging on the top of your computer) may either cause the joint to regain contact -- or it might cause a functioning joint to lose contact. Installing a fan inside the computer will (to a limited extent) solve the heat problem. But it will do nothing to prevent "vibrations from causing the joint at the defective solder joint to break the electrical connection. THE SOLUTION: Remove the power supply board and resolder the wiring-harness pins to the power supply board. The problem was caused by sub-standard manufacturing processes by whomever produced the Kaypro CP/M power supply boards. Most of the other components on the power supply board received ample solder, sufficient enough to ensure a permanent bond. However, since the pins in the wiring-harness that distribute electrical power to the rest of the computer are "thicker" than other component connections, they require more solder to hold them to the board. In order to make up for this deficiency, you merely need to add more solder to that already present at these joints. Anyone who has any experience with a soldering iron can do this -- no computer chips are involved, no "small" or "sensitive" components are involved, and it would be difficult (but not impossible) for you to damage the power supply board when you are adding solder to the wiring-harness joints. It took me only 60 seconds to complete the soldering. The problem has completely disappeared! As a result, I don't need to spend between $2,000 and $4,000 for a new computer (at least not right now, anyway!). If I need MS- DOS for anything, I will use my "work" computer. My CP/M Kaypro will continue to be my primary "home" computer. And for a few weeks, I was actually beginning to believe that CP/M was dead! I was getting ready to bury it when I figured out how to bring it back to life. For additional information concerning this CP/M Kaypro power supply problem, see the May 1987 PROFILES, page 69 and the Nov- Dec 1986 (Vol 4 No 6) Kugram, pages 6-7. I would strongly recommend that anyone who is having "strange" problems with their CP/M Kaypro should go ahead and resolder the power supply wiring-harness joints before they start looking for the problem elsewhere.