[HECnet] My VAX lost its mind!

On Wed, 5 Feb 2014, Dave McGuire wrote: On 02/05/2014 04:17 AM, Mark Wickens wrote: Fans would click for a second and then kick right back off. It stopped doing that until I removed all the drives. Plugged 'em back in after opening the PSU to look for obvious faults and found none. Everything is working fine now...Strange. I had a hard disk taken out by a power spike. I also had firmware corruption that required reflashing the EEPROM, but I don't remember if that was related to the PSU. They draw 30 watts when switched 'off' so it's definitely worth turning them off when not in use. Twitching fans might indicate over-current protection kicking in. If it's a repetitive twitching, it's probably the error amplifier or the voltage divider feeding it. (those will be difficult to test individually unless they're discretes, of course) It was a single twitch and it then kicked right off. Light never came on. One other thing I've seen recently with older switching power supplies is the output capacitors' ESR going up due to age, causing their time constant to exceed that of the regulation loop...creating, you guessed it, an oscillator. That would certainly explain it. It wouldn't explain why they went back to normal later...unless they're temperature sensitive. I know one thing however - switched mode PSU experts are few and far between! This is painfully true. I *design* the damn things and I shy away from working on them most of the time. Direct AC-driven ones are RIGHT OUT in my book. I prefer linear supplies with simple rectification. ;) I understand /those/! -Dave -- Cory Smelosky http://gewt.net Personal stuff http://gimme-sympathy.org Projects