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Old 12-09-2016, 12:14 PM   #1
Morsus
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Default Watson AS4541 no power

Hello,
I'm not much into audio equipment but I have to be atm.
This woofer started working every other day until it finally died.
Even led indicator wont power up at all. I opened it up, everything looks fine but I replaced 3 caps at the power supply board with the same ones. Tried it again, no luck. Fuse is fine, transformer is fine (giving 119V on output).
While its disassembled like this I started it few times and I noticed the 'click' sound somewhere on the boards each time I plug the woofer into the wall. This sound stopped when I disconnected all the cables (to make sure its not on power board).

Can you point me out at what should I check next. Thank you.
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File Type: jpg IMG_20161209_183659.jpg (537.0 KB, 15 views)
File Type: jpg IMG_20161209_183905.jpg (358.0 KB, 8 views)
File Type: jpg IMG_20161209_191625.jpg (506.1 KB, 16 views)

Last edited by Morsus; 12-09-2016 at 12:19 PM..
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Old 12-09-2016, 12:38 PM   #2
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Default Re: Watson AS4541 no power

Does it has bypass switch to turn on the unit without requiring the present of the audio signal for it to come on?
What DCV do you have between the two legs of each one of those two large filter caps for the +/- power supplies?
The clicking is probably comes from that blue relay on the power amp board.
Pictures of the panel showing the input jacks, switch, etc.?
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Last edited by budm; 12-09-2016 at 12:39 PM..
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Old 12-09-2016, 01:37 PM   #3
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Default Re: Watson AS4541 no power

I don't understand about bypass switch. I am guessing no, at least the led should work even without any audio input/output.
If you are talking about the biggest caps, the voltages are 0.26V and 0.3V as shown on the picture. I hope I measured correctly.
Here is the picture of both front and back panels.
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Old 12-09-2016, 01:46 PM   #4
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Default Re: Watson AS4541 no power

OK so what kind of ACV do you have between Black wire and the two Yellow wires on that secondary side of the power transformer?
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Old 12-09-2016, 02:36 PM   #5
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Default Re: Watson AS4541 no power

Both yellow - black are 12V AC. (11.8-11.9 to be exact)
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Old 12-09-2016, 02:55 PM   #6
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Default Re: Watson AS4541 no power

OK, looking at the bottom side of the board:
http://www.badcaps.net/forum/attachm...0&d=1481312033
I can see that those two filter caps will not have any DCV (it should have about 16VDC) on them until that blue relay is turned on, so there must be another power supply section on that board that always has the power all the time to run the circuit that will drive the relay coil.
I see another filter cap (C506?) right next to the power transformer connector, check and see what DCV you have between the two legs of that cap:
http://www.badcaps.net/forum/attachm...9&d=1481307564
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Old 12-09-2016, 03:45 PM   #7
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Default Re: Watson AS4541 no power

Just to mention I disconnected all the cables from boards while doing measurements.
I have just measured the C506 cap and I do get 15V DC. I will connect all cables back and do the same measurements.
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Old 12-09-2016, 04:18 PM   #8
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Default Re: Watson AS4541 no power

Quote:
Originally Posted by Morsus View Post
Just to mention I disconnected all the cables from boards while doing measurements.
I have just measured the C506 cap and I do get 15V DC. I will connect all cables back and do the same measurements.
Well, that is very important to have the power transformer connected to the board otherwise you will not have any Voltages to run the board.
Recheck the Voltages on the two large filter caps again.

Last edited by budm; 12-09-2016 at 04:20 PM..
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Old 12-09-2016, 04:24 PM   #9
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Default Re: Watson AS4541 no power

When I said I disconnected everything I meant everything BUT transformer, my bad :S

Connected everything back and I got next readings on caps. I measured DC only.
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Old 12-09-2016, 07:39 PM   #10
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Default Re: Watson AS4541 no power

So now you do have the relay on and the two big filter caps for the +/- supplies have DCV on them for running the amplifier ICs (the ICs (6 of them) mounted on the heat sink).
So now you need to check the Voltages on the other 2 boards to see what Voltages you have feeding them from the power amp/power supply board. it is not going to be easy since you do not have the schematic but you can at least get the spec sheet of the ICs to get the pin out of the IC to find out which pin are for the VCC pins.
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Old 12-10-2016, 02:47 AM   #11
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Default Re: Watson AS4541 no power

put plastic sheets between the amps tda's and heatsink only one of them has that sheet that protects them from shorting togheter
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Old 12-10-2016, 05:51 AM   #12
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Default Re: Watson AS4541 no power

Can you tell me what IC stands for?
You can see the markings on these, I am guessing that this is the datasheet.
Couldnt I just measure the voltages on the cables that connects to these boards?
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Old 12-10-2016, 09:50 AM   #13
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Default Re: Watson AS4541 no power

Those marked with "2030" are cheap chinese clones of ST TDA2030.

Tab is connected to negative voltage. As dragos says, it’s recommended to insulate each IC from heatsink with a mica or plastic foil (not *any* plastic, use one scrapped from any PSU). Anyway, if nothing else touches (electrically) the heatsink, this cannot be the cause of failure. It’s something to check.

Last edited by Chungalin; 12-10-2016 at 09:56 AM..
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Old 12-10-2016, 10:35 AM   #14
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Default Re: Watson AS4541 no power

But if I screw that in it would still be connected to the heatsink..
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Old 12-10-2016, 11:06 AM   #15
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Default Re: Watson AS4541 no power

I feel stupid for doubting this. I had some of the thermal pads laying around so I used those. Here is how those look like now. And how the woofer looks like. ^_^ I hope this is not a short term solution. Thank you everyone!
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Old 12-10-2016, 02:03 PM   #16
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Default Re: Watson AS4541 no power

Blah, it stopped working.... -.-
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Old 12-10-2016, 02:09 PM   #17
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Default Re: Watson AS4541 no power

http://www.badcaps.net/forum/attachm...0&d=1481389518
Something is not making sense as you can see that the mounting screw fro the top IC has white plastic washer to isolate the mounting screw from the heatsink so the tab of that IC will not have electrical contact with the heatsink, the other 5 ICs that you add the thermal pad to them do not have the washers to isolate the mounting screws from the the tab, so basically if you check the resistance between the heatsink on those 5 IC tabs, it will show electrical connection.
I doubt that was the cause of the problem due to missing thermal pads, also the DCV reading would have come out wrong on those two filter caps.

Last edited by budm; 12-10-2016 at 02:12 PM..
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Old 12-10-2016, 02:36 PM   #18
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Default Re: Watson AS4541 no power

Maybe a bad/cracked solder joint or bad connection on that board and whilst its been out flexing etc made it work tempory.
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Old 12-10-2016, 03:24 PM   #19
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Default Re: Watson AS4541 no power

I just checked the connection between each of the ICs and heatsink. Turns out ALL IC (including the left one that has plastic washer and plastic isolator) ARE connected to the heatsink. So the thermal pad/plastic AND plastic washer for screw are totally useless.
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Old 12-10-2016, 03:38 PM   #20
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Default Re: Watson AS4541 no power

Uhm I have just checked the connection between all of the ICs and heatsink and they are all connected. Even the one on the far left that has the plastic washer on the screw and a plastic isolator. After unscrewing the same from the heatsink and moving it away from heatsink so it has no possible contact it still has a connection between the IC housing and the heatsink.
You can see on this picture that the heatsink and middle pins of these ICs are actually connected and it is ment to be that way. Still makes not sense on putting a plastic protector and a plastic washer on that screw when it is already connected by pins.
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