My VAX4000-500 will no longer power up, with the PSU starting up and then immediately shutting down. I suspect a possible short somewhere. I have measured the resistance of the load presented to the PSU by connecting probes to the backplane sockets used to power the machine. The odd one is the 5V load. With all the boards in and drives inserted I measure a resistance of about 4R. As I pulled out boards, drives and fans, it gradually crept up to 6R. So with nothing connected to the backplane I get a 6R load across the 5V supply.
To my inexperienced mind, that seems a bit low. Should I expect such a value, or should I be dismantling the box to investigate possible shorts or failed components on the backplane? Additionally, the 12V side seems to be charging a capacitor as the resistance slowly climbs to about 130K. Is that reasonable? Again, nothing but the backplane. The 3.3 and -12V show very high resistance at all times. Thanks Rob