Chattering Relay in Krell KSA-250

[K-amps]

So I take the plunge and buy a Krell KSA-250 from ebay. Powered it up and find one channel's relays are chattering. Bzzz Bzzz Bzzz

(applying finger pressure to the cap of the relay mutes the sound but I can still "feel" the buzzing)

I have not checked DC offset or DC at the outputs and am "hoping" that this is only a symptom of a dried out smoothing cap on the relay's coils.

Any experiences are welcome:

Additional note: It is the speaker engaging relay; not the power up relay. This is the one that engages after 2 sec delay.

thanks!!

PS: Written to the seller.... no reply yet... why am I not surprised?

[johnnyx]

Does it buzz after a 2sec delay or does it buzz immediately?
If it's 50 or 100Hz buzz, then it could very well be a dried up cap.
If it's on a seperate "protection" pcb then it will make checking the components easier.
It could also check for a dc offset at the output though, so it's a good idea to measure that, but I don't think that would give a buzz. It's probably not a big problem to fix.
Good luck

[K-amps]

As I said, the buzz is not immediete but after the protection circuit engages the speaker relays after 2 seconds or so.

Thanks for your comments.

[destroyer X]

Put a diode in relay coil, also invert it fast to see if it works without noise.... no result?.... put small condenser and will increasing it till 22 uF... no result.

DAMAGE!, real problem, DC off set...over current, over voltage, Lower voltage, transistor that controls the relay, or need a finger on it (ha ha ha, smile, please).... sometimes a rubber can be good to avoid vibrations.... because to much search, sometimes we make a short with the multimeter points and...bummmmm!

Carlos

[K-amps]

Carlos,

I am sure Krell would have put a diode on the relay coils... the condensor/ capacitor is what I hope is the issue.

No DC offset at all, the amp plays good.

K-

[destroyer X]

So, go on doing this good job.

Thank"s to inform me that he already knows.

Carlos

[K-amps]

Carlos,

You look much more distinguished with a greying beard/Gotee ... the older photo does not have much character.

Off to the nearest Churrascaria!!!

[EchoWars]

If the relay circuit uses a transistor to engage (and it likely does), then I'd suspect it's either got too much C-E voltage on it (won't saturate because of age), or just plain leaky from C-E. Pretty common.

[K-amps]

Echo,

It does engage the relays, now as I keep it on for a while, the sound of buzzing is low... the amp plays ok...

Wouldnt you say that the chances of a aged cap is higher?

K-

[EchoWars]

From my own experiance...no. I mean, both are certainly possible, but for relays, the engaging transistor operates continually in a saturated state. C-E voltage rising or leakage from aging is pretty common...and on units I restore, the driving transistor gets replaced as a matter of course.

Chattering is not good for the thin plating on the relay contacts ..it will pit and wear them quickly.