Help no power to subwoofer

L8on

Novice Member
Hello yesterday I bought a monitor audio gsw12. Last night it worked great and this morning it wont turn on. No power led on the back and no top screen. Fuse in the plug and in the subwoofer are both fine. Checked with a mulit meter and I'm getting 240 on the mainboard.switch works fine tested.... Took the back plate with mainboard to a locat audio specialist and the said they cant get hold of a new board and cost of fault finding would be great as there are no obvious faults I.e blown capacitor,scorch Mark's. Anybody in the know that could help me out any help would be much appreciated:) I have attached a picture with voltage readings
 

Attachments

dobrykamil

Active Member
Remove power supply board, and find 8 pin IC underneath. Measure and let me know, what voltage do you get between pin 5 (GND) and 7 (VCC).
 

L8on

Novice Member
Remove power supply board, and find 8 pin IC underneath. Measure and let me know, what voltage do you get between pin 5 (GND) and 7 (VCC).
Hello thanks for your reply. I cant see an 8 pin connector under the board, everything is a soldered joint. Please see this attached photo of my board :)
 

Attachments

dobrykamil

Active Member
Please remove psu board (red), keep two wires connected (yellow) and disconnect wires (green) for now.
Underneath power supply board, find 8 pin chip. Then apply mains AC and measure V between pin 5 and 7.
 

Attachments

L8on

Novice Member
Please remove psu board (red), keep two wires connected (yellow) and disconnect wires (green) for now.
Underneath power supply board, find 8 pin chip. Then apply mains AC and measure V between pin 5 and 7.
Hello I'm getting 0v across ins 5 and 7 ...that's the top left (5) then miss 1 (7)
20200804_180857.jpg
 

dobrykamil

Active Member
Just to be clear, 0v between pins 5 and 7?
20200804_180857.jpg
 

dobrykamil

Active Member
1V is way too low. That IC needs at least 16V to start oscillating. Now, let me know value of the R27. I believe it's located between those two large capacitors.
20200804_164352.jpg
 

L8on

Novice Member
1V is way too low. That IC needs at least 16V to start oscillating. Now, let me know value of the R27. I believe it's located between those two large capacitors.View attachment 1345252
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R27 is reading 327v is that right? After double checking you diagram pin 7 watch 6.3 v not 1v. Sorry to be a pain just trying to keep my head above water ... this isn't my speciality 😁
 

L8on

Novice Member
R27 is reading 327v is that right? After double checking your diagram pin 7 was 6.3 v not 1v. Sorry to be a pain just trying to keep my head above water ... this isn't my speciality 😁
 

dobrykamil

Active Member
Sorry, I meant resistance of R27. Power everything off, set multimeter to Ohm and let me know its value.
 

L8on

Novice Member
It's very strange as it keeps changing it's now showing 6.8 and the value is coming down slowly... is that normal :)
 

dobrykamil

Active Member
Ok, here is a very important question, 0.585 of.. kOhm, mOhm? Can you post a photo of your multimeter's display during measurment? I believe it shows 0.585 mohm=585 kOhm which is 300 kOhm more than original value. That R27 resistor should be 300 kOhm 1W. Something like this one. If I'm right, then you'll need to replace it.
 

L8on

Novice Member
Ok, here is a very important question, 0.585 of.. kOhm, mOhm? Can you post a photo of your multimeter's display during measurment? I believe it shows 0.585 mohm=585 kOhm which is 300 kOhm more than original value. That R27 resistor should be 300 kOhm 1W. Something like this one. If I'm right, then you'll need to replace it.
I beleave its mhoms here is a screen shot
20200804_211402.jpg
 

dobrykamil

Active Member
Ok, I was right. Almost 600 kOhm. Thats your culprit. Order one from my previous message.
 

dobrykamil

Active Member
Hello pal my resistors come today and I swapped out r27 .... everything is now working. I cant thank you enough for your help 😃
Happy days. I’m glad I could help.
 

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