Relays, Capacitors, and Blown Speakers

I've seen many cases over the years where the speaker relays internal contacts get dirty/oxidized etc. with the effect being low level noise/hash. cranking the volume up loud or power cycling will sometimes improve the connection for a short time. I've had this with several amps including an old KSA-150. As Magfan states, the relay(s) could also hard fail totally and not engage, or even "stick on". I've never seen these failure modes, but definitely not impossible... with the "stuck on" being the only obvious relay failure mode that could conceivable cause speaker damage.

I've also owned and re-built probably a dozen or so old Marantz 22XX and Heathkit AR-15XX series.

In my case I've never done any "cap-jobs" and have never had any failures. Some people swear by replacing all or as many as possible caps. Obviously if there were reports of a specific component failing, then no doubt.

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.