Yorkville YSM6

[bsco]

I have this near field powered monitor and when powered down makes a very loud pop in both the speaker and tweeter....The mute fet for the woofer is working fine...if you short the drain and source the woofer amp is muted...... There are mute pins of the LM3886....and when measured they are at -2.5vdc....the mute signal for the tweeter comes from the -20V supply, goes through a voltage dropping resistor and then to a 7.5V zener diode......the cathode of this diode then connects to pin8, the mute pin for the tweeter.....is there supposed to be -7.5v here?? and with the woofer mute circuit working, I am leaning towards something wrong in the power supply...but can't find anything out of the ordinary......Any suggestions??? Attached is a schematic....
Cheers

[g1]

The mute only works for turn on, so as you suggested, collapse of supplies at turn off could be a cause. Woofer and tweeter run on different supplies so I think you can rule them out as the problem is in both. That leaves the +/-15V supplies.
Try scoping + & - 15 rails at the same time and see what happens at power down. Also check to see if there is a spike at the input of the power amp chips when power is turned off.

[bsco]

Ok g-one...Thanks for the reply.....I did check the dc levels of the 15V supplies...but never scoped them...I will check that tomorrow and let you know what I find...
Cheers,
Bernie

[bsco]

Hi g-one..I have a question...If I turn this unit off with the power switch it will make this loud pop in both tweeter and woofer.....If I leave the power switch turned on and I pull the plug there is no sound.....the pop is gone....and I tried both ways a number of times to make sure.....maybe I have a problem with the switch??here is a suppressor cap connected across the ac input directly at the rear of the AC mains receptacle...but that is before the switch...I will have to strip this down so I can get at the switch....not much room in there....hopefully I am on the right track here....
cheers....

[Enzo]

Good, you anticipated the next question already.

The common reason for power switching pops is arcs in the switch contacts. Some switches arc more than others. The amp amplifies the sound of the spark as it discharges.

Yes, a snubber cap across the switch might solve the entire problem.

[bsco]

Thanks Enzo...I have a couple of caps here for that....(.22uf at 275Vac)I'll try that.....but was also thinking of replacing the switch as well........but all these units are cheaply made....maybe there was a bad batch of switches on a particular run....I'll check it out and see what I find....Thanks for the reply...
Cheers

[52 Bill]

Did you try cleaning the switch?

[bsco]

Actually, I did 52Bill.......It worked for a little while then started to happen again.....So I am going to connect a snubber cap across the switch terminals the switch is a new one and I am thinking that it is a manufacturing issue....(cheap parts made in China)........I did this already with a set of jumper leads and it worked out fine....I used a .22uf cap as that was what I had on hand just for a test...I was planning on installing a .1uf cap there......it's physical footprint is smaller.....thanks for your reply...It is much appreciated...
Cheers...

[bsco]

I installed that cap across the switch after and it worked out great....problem solved...A big thank you to everybody who helped me out.....
Cheers.....
P.S. Now...to get on to the the next item that is up for grabs...

[squirrlyj]

I am having the exact same problem, Would you be able to provide a link to the parts you used to replace the switch?

Im not really sure what I should be looking for, I was going to buy any old toggle switch and try to install it but then I saw this thread while searching