Relays, Capacitors, and Blown Speakers


OK, so I just picked up a used NAD 2400PE, a 100W circa 1990, because I love the sound of my old 7225PE receiver from the same era. After doing a bit of research on this particular amp, I see that it and its 2000-series brethren were prone to speaker relays going bad. In addition, the amp and its original caps are 20 years old. My question is, when a speaker relay, output, or large cap malfunctions, is the speaker automatically in mortal danger from DC or something else? This particular model has 40,000uF in its supply, BTW. Any input would be much appreciated and help allay my fear of using the amp w/good speakers.
bojack
I think what Magfan maybe referring to, besides a fused-closed set of relay contacts, is the circuit that controls the protection relay's coil can fault during initial system power-up (or is permanently damaged), which is usually delayed until after full system stabalization (several seconds), thus the "click" sound one hears. Same goes for power-down where the relay drops out first to protect speakers while the amp's voltage drains off slowly.

This is a typical relay controling method in all kinds of equipment, usually triggered by IC's which do fail "open" or "latched".

FWIW,
Frank
Right you are, Metro.
Their is also a class of part called 'time delay relay' which is internally controlled to enable the circuit a given amount of time after receiving the 'on' command.
These also fail and will sometimes latch in either open or closed conditions.

years ago I had a special set of files used for dressing relay contacts which had stuck or 'fused', as Metro ref's.
Wait, I know this one! "Alex, what are burnishing files?"

...And right you are regarding TDR's.