hans@umd5.umd.edu (Hans Breitenlohner) (07/24/87)
I helped a friend with a power supply problem on his 130XE this weekend, and thought I would pass on what we found in case anybody had similar problems. He had expanded a 130XE to 320K, and everything seemed fine. Then he expanded it to 576K, and everything still seemed fine. But after a while the following problem occurred: After the machine had been on for an extended period (many hours to a day), and then was turned off, it would not power up correctly. The screen would turn black, and nothing else would happen. Turning it off for a while seemed to fix the problem. With the help of a scope we found that the power supply, when hot, would not supply 5 volts on powerup. It would oscillate at 105 kHz around 3 volts. The unit pulled only 900 mA, and the supply is rated at 1.5A, so overload was not a problem. It turned out that any disturbance, such a inserting a VOM in the supply line, would make the problem disappear (which made chasing it down real fun!). The final solution was to put a small choke (about 10 micro-Henry, but I don't think the value is very important) into one of the power supply output leads, and the problem has not been seen since. I don't know if this is typical behavior or if the power supply was defective. Does anybody know what kind of regulator is in the supply? It was great fun, I hope somebody can use this info.