Pulsating sound when I turn on my SCA rack.

[Nu-tra]

Any Ideas? Sometimes it's fine when I turn the rack on and sometimes the light will flash and sound will pulse. All N72's and a PS03 I think.

[tpryan]

Does the pulsing eventually stop? What happens if you disconnect some or all of the modules?

[Nu-tra]

Sometimes its stops quick and sometimes it goes a for a while. I just opened the unit to test.

[Nu-tra]

It seems to happen more often when the phantom power is on about 5 channels. I bought this chassis used he said it was a little over a year old so i dont know what power supply version it is. When the power does pulse the center led is the one that flashes while the other two are waiting to light up.

[Nu-tra]

When I disconnect the second module from the power supply the center led does not light up. Strange

[tpryan]

What version of N72s? Do any/all have the large 3K9 resistor (R41) close to the power connector? If not, you may want to tack that on to see if it makes a difference. See the current schematic for details.

[Nu-tra]

Copy that. I will check

[Nu-tra]

What version of N72s? Do any/all have the large 3K9 resistor (R41) close to the power connector? If not, you may want to tack that on to see if it makes a difference. See the current schematic for details.

Only 2 of the 8 N72's have the R41 Resistor.

R40 looks like a different value as well as the R41 on my older N72s is a smaller (in size) resistor. R41 is near the large heatcsink on my older ones.

[Nu-tra]

I also noticed my input transformers on 6 older units have no visible insulation under the input transformers.