API trouble

[solderjockey]

Hi DIYers - I received a lot of great info on this site to build a c12 { and then 251 } so Thanks . Hope i can get some help with an API 3124 - A few years ago it had an intermittent phase switch. I called the company and was told what to do and was sent a switch free of charge . Recently I called with a one or two second later power surge on shut down . this would thump the system. I believe API changed ownership recently, well the technician told me it shouldn't do that with no advice or a schematic. Maybe some one here has a similar issue. Thank You kindly

 

[pucho812]

Thump is usually dc.
Check capacitors and replace as needed.

 

[solderjockey]

thanks pucho812 - a visual detected no bad caps - would have to remove to test. Would the big P.S. caps be #1 suspects? - Also to remove the power supply board there is the long power switch located above that and it looks like some kind of glue on the switch and switch. extender. anyone know if that comes apart at the switch? Thanks for any and all help.

 

[sodderboy]

Usually, an intermittent switch is improved with local contact cleaning/conditioning. Perhaps the description to the API tech indicated a different direction? Switch replacement is usually for a mechanically defective switch, or where there is no hope for cleaning decades-old dirty contacts.
Standard operation is not to listen to stuff when you power up/down where a speaker could be damaged. TECH 101, day 1. Like you deadpatch amp inputs at a patchbay (or turn THEM off) when turning a console off/on rather than listen to it pop a speaker. Console channels or monitor outs are muted when stuff is powered down at end of day, if its even turned off at all.
If you have it in some 24-7 system where it has to be borrowed while everything else is still working, then disconnecting the cables before power transition is an option.

I wouldn't muck about inside any equipment looking for a reason why it makes a noise when powered on or off. If it is quiet and operating properly when it's on, use it without worry. As the fortune cookie says, "Never trouble trouble, till trouble troubles you".
Mike