My experience with VDD shorted to GND on the main board is that it¡¯s usually but not always in the MPU chip. ?You can determine that with a milliohm meter. ?Find where on the board the lowest resistance is from VDD to GND. ?Sometimes it¡¯s a single pin on the MPU or sometimes it¡¯s the supply lines to the MPU. ?The over voltage that causes this is often a mistake in building or a solder bridge or a probe slipping when measuring. ?If 5V or 12V gets put onto any of those MPU lines, it¡¯s all finished. ?The MPU can be replaced. ?I¡¯ve done it a couple of times. ?But other chips could be damaged as well. ?Also replacement MPUs are expensive and to date not available from Hans by themselves. ?I¡¯ve always salvaged them from known working boards.
Jeff
W1NC
