powered sub wont come out of standby

[moss99]

Hi all , I have a monitor audio powered sub AW-12 which has an issue , the issue im having is it won't come out of standby , the led started flickering between green (active) and red (standby) now just stays red , I've ruled out the input end ..
it is made up of 3 boards see photos . ive tested the transistors (arrowed green) and they are ok . The way the boards are held together with aluminium panels which double up as heatsinks for the transistors so when its assembled i cant get to the boards to check voltages ,

[CapLeaker]

Re: powered sub wont come out of standby

Put that thing together, heat the PSU up with a hair dryer to like 40C and see if it fires up again.

[tibimakai]

Re: powered sub wont come out of standby

I have a very similar issue with an Onkyo SKW-540. It comes out(led is green), but no sound. Sometimes there is sound, but most of the time, there is none.
I will be following this thread.

[madan1]

Re: powered sub wont come out of standby

I also put my money on the psu board.

This... "thing"* ( I'm trying to be politically correct here ) can be assembled and turned on without the radiator attached... of course only for testing purposes without any significant load.


*I'm not familiar with that trademark, but from the pics looks like a total piece of.... and I guess it doesn't sound better ( class D... )

[petehall347]

Re: powered sub wont come out of standby

clip the heat-sinks on if worried about it ..
then check regulators in supply

[budm]

Re: powered sub wont come out of standby

See that relay on the board? When the unit senses the audio input the unit will come out off the standby and that relay will be on, when the audio stops coming in, then about 10~15 minutes later the unit will go into standby. That is typical setup for most sub woofer.
So check and see if the power supply is stable or not, if it is, the do you hear the relay even comes on or not.
We need t o see the bottom side of the board to verify the relay function since it is single pole then it may be just the speaker protection relay.

[jazzie366]

Re: powered sub wont come out of standby

Hi all , I have a monitor audio powered sub AW-12 which has an issue , the issue im having is it won't come out of standby , the led started flickering between green (active) and red (standby) now just stays red , I've ruled out the input end ..
it is made up of 3 boards see photos . ive tested the transistors (arrowed green) and they are ok . The way the boards are held together with aluminium panels which double up as heatsinks for the transistors so when its assembled i cant get to the boards to check voltages ,

Do this to start:

Get a 9v battery and some probes, find the two control pins on that relay, and bridge the 9v across them. If you hear a click, take the battery away. Do not hold the battery to the leads for more than a couple of seconds to prevent damage.

If the relay clicks, it's probably fine but could have burned contacts internally, but we'll assume they're okay for now.

Get a multi meter and check for continuity across the fets or transistors on the board. The ones in the TO-220 package are the ones I'm referring to (metal tabs on top and back). If none have shorts, then we'll have to go to the smaller components on the board.

I'm betting a small bit on those International Rectifier fets. I found the datasheet, they're HEXFETS made for SMPS. I've had those in Alpine amplifiers and I've found that under high heat applications like in car amplifiers, they blow pretty easy.

[budm]

Re: powered sub wont come out of standby

"Get a 9v battery and some probes, find the two control pins on that relay, and bridge the 9v across them. If you hear a click, take the battery away. Do not hold the battery to the leads for more than a couple of seconds to prevent damage."

OP must verify the polarity of the snubber diode connected in parallel with the DC Coil of the relay first, if you hook up the battery wrong you will damage the diode.
Better way is to find out if you do have DCV on the relay coil or not.
BTW, relay is 12VDC.

[jazzie366]

Re: powered sub wont come out of standby

"Get a 9v battery and some probes, find the two control pins on that relay, and bridge the 9v across them. If you hear a click, take the battery away. Do not hold the battery to the leads for more than a couple of seconds to prevent damage."

OP must verify the polarity of the snubber diode connected in parallel with the DC Coil of the relay first, if you hook up the battery wrong you will damage the diode.
Better way is to find out if you do have DCV on the relay coil or not.
BTW, relay is 12VDC.

I've done it this way for years, never had a problem. Are you sure such a low voltage will really damage a diode?

[moss99]

Re: powered sub wont come out of standby

Thanks for all the replies , i will have a look at it after work , Monitor audi surprisingly sent me the schematics !

[moss99]

Re: powered sub wont come out of standby

Im getting 100v Ac on all pins of the 11 power transistors in the 2 boards .
I have a bench power supply for testing if needed

[moss99]

Re: powered sub wont come out of standby

Im getting 100v Ac on all pins of the 11 power transistors in the 2 boards .
I have a bench power supply for testing if needed

[madan1]

Re: powered sub wont come out of standby

ac?
are you sure?
On all schematics there is a rectifier bridge right after the power input.

[moss99]

Re: powered sub wont come out of standby

Ah , no sorry my bad , i had my negative tester lead on the AC ground , the voltages at J5 , J6 and J7 are all correct at the output board . also i can hear the relay click when i shut off the power .

[budm]

Re: powered sub wont come out of standby

I've done it this way for years, never had a problem. Are you sure such a low voltage will really damage a diode?

Do the experiment using 9V connect to the diode in the forward mode ad see how much current it will draw.
The relay will not come on either if the diode is bias on.
And how about 24V or 48Vdc relay, you may not be so lucky the next time.

[budm]

Re: powered sub wont come out of standby

Thanks for all the replies , i will have a look at it after work , Monitor audi surprisingly sent me the schematics !

Too bad they did not send you the pre-amp/ power amp sections too.

[moss99]

Re: powered sub wont come out of standby

Too bad they did not send you the pre-amp/ power amp sections too.

I thought something was missing , I have emailed asking for the missing one ,
here is a photo of the back of the board , the relay is in the circled section .

[madan1]

Re: powered sub wont come out of standby

Q9-Q11 (above d11-d14 on the last photo ) is this the original soldering?


by the way ( for the ppl doing this for longer time ), is it normal practice to cover the whole pcb with this black goo?

[moss99]

Re: powered sub wont come out of standby

No I took these out to test them

[madan1]

Re: powered sub wont come out of standby

I do not know why everyone focused on the relay... in the first post it is said that "the led started flickering between green (active) and red (standby) now just stays red" we should get the green led again and then if the issue persists check the relay.

So do the heating test first, then change all caps... or just skip the test and change the caps. At least this is what I would do if had to work blind ( without checking the V lines )