MAC 4100 turnoff thump

[mrz80]

Was there a service bulletin issued against the MAC 4100 to deal with that irksome turn-off "thump"? I know that the problem of "thump" noises on turn-on and turn-off cropped up and got dealt with on several other Mc items.

When the 4100 is turned off, the output stops, then the output meter LEDs all light up, then comes the "thump" from the speakers. It can be mitigated by turning the volume all the way down before hitting the power switch.

 

[skippy_ps]

Sounds like the speaker relay is stuck closed. Omron LY2-DC48.

Murray

 

[woodlander]

If your speakers are connected via the standard connection on the back, your unit has a problem. My MAC4100 doesn't do that. I am afraid I don't know enough to recommend a fix, but several of the regular posters here probably can help.

 

[dewickt]

First question is does it go click about 2 seconds after turn on, this would indicate the speaker relay was getting it's proper turn on delay. If it makes no sound or goes closed immediately on turn on you have a hung relay (no click) or a bad relay driver (no delay).

 

[mrz80]

First question is does it go click about 2 seconds after turn on, this would indicate the speaker relay was getting it's proper turn on delay. If it makes no sound or goes closed immediately on turn on you have a hung relay (no click) or a bad relay driver (no delay).

I just checked on that. There's about one second of delay before the relay clicks on power on. And the last couple times I power cycled it, I didn't get a turnoff thump; I heard the speaker relay click and cut off the sound just before I saw the light show on the meter LEDs. I'm wondering if maybe the relay (or something in its driver circuit) is thermally tempermental, as I usually leave the unit on for hours at a time.

 

[dewickt]

Pull the pre to amp jumpers on the rear and see if it still goes thump, this will narrow it down to preamp or amplifier sections. Jumpers out and no thump says preamp problem, out and still a thump it is an amplifier problem, this cuts the trouble shooting in half.

 

[Scott Norton]

Pull the pre to amp jumpers on the rear and see if it still goes thump, this will narrow it down to preamp or amplifier sections. Jumpers out and no thump says preamp problem, out and still a thump it is an amplifier problem, this cuts the trouble shooting in half.

I am having an odd problem with the power-on/off delay on my 4100. The receiver has no delay when it is powered on and a few second delay when it is powered off. It is my understanding (from another poster on this site) that this is backward (the delay should be when the 4100 is powered on and no delay when powered off). Since I have no power on delay, I hear one loud pop every time I power on the receiver. The receiver also produces a lower volume pop when I power off the receiver. The popping volume on both power on and power off is unaffected by the volume control and occurs on all input selections.

I have verified that 48vdc is getting to the speaker protection relay coil immediately after the receiver is powered on. I have also verified the relay is operating correctly. Can you identify the components associated with the delay circuit or how I can get the correct power on and power off delay?