Threshold 500II

[Dpeters]

I have a problem with my amp. I have it hooked to a 7.1 surround pre out. I run the Thres. to my main speakers. When the surround amp switchs channels, it make a loud click from my right channel main speaker only. Someone has said it sounds like a capacitor discharging. I've switched the wires over from left to right on the main capcitors but the click still comes from the right side. What do you think?

[GRollins]

Check for DC offset at the input to that channel.

Grey

[Dpeters]

Thanks. I know how to check the D/C output at the speaker output, but not sure how to check it at the input. Could you please explain?

[eyoung]

Grey may be refering to dc offset at the pre-out...

Elwood

[Dpeters]

Are you referring to the pre out on the 7.1 amp? If so, I have reversed the L/H and R/H channels at the pre out and the click sound is still from the right channel. Therefore I have eliminated the pre out as the source.

If not, would you please explain.

[georgehifi]

These are usually bullet proof amps one of Nelsons favs,except for one problem component, for memory either C4 or C5 was a value .1uf tantalum cap and when they went leaky they gave problems like your experiencing, and when they failed, " BANG!!!!" everything goes from output back to input, change this cap for the same value plastic polyprop and hope this fixes your problem.

Below is the circuit for the S300 MkII optical I believe the S500 was the same but for more outputs tranies, higher rails, and a dual power supply instead for single.

And next post is the operating parametters measurments.

Cheers George

[georgehifi]

There ya go!

[Dpeters]

Thanks. It looks like there is only one tantalum cap on the small board. It's very small and yellow in color. The markings are STC u22 35v. Do you think this is the correct cap? I am going to try to post a pic but do not know if it will work.

[Dpeters]

Thanks. It looks like there is only one tantalum cap on the small board. It's very small and yellow in color. The markings are STC u22 35v. Do you think this is the correct cap? I am going to try to post a pic but do not know if it will work.

[georgehifi]

Yep, that looks familiar, that value is .22uf 35v, change it for a .22uf 100v plastic and hope it was the problem, it's good to chage it anyway as tantalums have a definite use by date and that one is a time bomb, for that amp.

Cheers George