modern switching power supply faults

Hi I to have a problem with one. It is similar to your first one. Basically, the first problem is that something is failing to start the switcher feedback. What happens on powerup is that it is given one kick. This gets the 12v going to the regulator circuit. It is then suppose to send pulses through the pulse transformer to fire the switching transistors. It could be most anything in the regulation loop. I fixed one in the past when I found an open wire in the pulse transformer. Still, it could have been anything in the feedback path, including regulator ICs, filter caps, diodes, resistors, etc. Mine is failing on a load related problem. As I connect more load, it fails to powerup. It is funny that it seem to be more sensitive to the loads that use the 12V. It seems to run the 5V loads fine. Your second one has most likely had a failed switching transformer and switching transistor. There could also be a load issue, such as shorted rectifier diodes on the secondary but that is unlikely. This would tend to keep the 12V from coming up and you'd get no pulses to fire the switching transistors. They're unlikely to fail if not turned on. Dwight _________________________________________________________________ More immediate than e-mail? Get instant access with Windows Live Messenger. http://www.windowslive.com/messenger/overview.html?ocid=TXT_TAGLM_WL_Refres…