The amp has no power. Is there an internal fuse for this unit?
Has anyone taken one apart?
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I have visually inspected the entire board multiple times and cannot see any evidence that would indicate shorted components, so I think I now have to start removing components to check for shorts.
Have you felt any of the components getting warm? A short will typically be very warm somewhere and that will likely be the culprit.
Small tip: If your components look good... put them back in. Its easy to lose the correct ones. If you want to leave off inductors and transformers, then thats fine.
Second small tip: Test what you can on-board/in-circuit. If it looks good, you can likely not worry about removing it. If it looks bad, then you can do a secondary test after removing it. That may prevent having to remove a lot.
So this is what I was hoping was not the culprit. But all is not lost if it is, I have replaced both of these on a repair once. I will tell you the easy way to get these off if need be. Found them on eBay from a stateside seller. Lots of the pins on the one side are supposed to be shorted together, but not all.. LOL
This I have found to be very very close to how Sonos has implemented the STA508.
http://www.st.com/resource/en/datasheet/sta508.pdf See Figure 7 on page 7.
m0untainman and I both have removed that same common mode choke, it separates the 36V power supply from the load.
So you can narrow down where your short is. We both had a rough time getting it back in. :-)
I would have given you the same advice that m0untainman did above, 'it probably aint the magnetics'!
Well guess what, I fixed one this weekend that had both of the windings of the common mode choke in the input filter (right after the diode bridge) blown open. Consequently the of the big storage caps threw up under it's top cap. Strangely there were no shorts and the fuse was not blown.
As for any other visible sign of a short, there does not seem to be anything. I have closely looked at all the caps, inductors and resistors and they look absolutely perfect. I am hoping that the STA508 is the root cause of the fail and replacing it will bring this baby to life!
All I do is solder all of the pins together on the side you want to remove. Then once there is a lot of solder across all of the pins keep moving your iron back and forth across all of the pins, the idea is to get all of the pins molten at the same time. Once you are liquid pretty much all the way across gently pry up the chip on the side with the solder. You will bend the leads on the side you have not touched. Then repeat on the other side.
FYI i lifted the pad from pin 18 on both the ones I replaced. But it is a no connect pin so no harm no foul.
After PMing gruv2ths, I am going to try putting the amp back together and powering it up with the STA508 removed. He said it should power on without it if there are no other issues with the amp. I will update this thread later today with my findings!
Wish me luck and fingers crossed!
For the first time, I now have 15.4 volts on the P-FET.
In addition all of the test points around the P-FET show their proper voltages
I still do not have voltage readings on the secondary output of the switching transformer that is controlled by the PWM
Not getting the flashing whit LED which indicates the amp is booting
The 36V and GND 36V test points only read 15VDC. This seems strange.
Could the PWM be causing the 0V readings across the secondary?
Dumb question but is the gray ribbon connected from the login board to the led/button assembly?
Also what happens if you plug in a active Ethernet cable to the back? Any network activity?
The RTN points on the secondary are shorted at 0 OHMS and I did have the ribbon cable plugged in when I powered the amp on.
I also plugged in a network cable to the port and there is NO activity.
Also just for giggles, I replaced the PWM again to see if that would help but it made no difference.
I have a bad logic board now that as soon as you push play it throws an error and you get no sound. And I have no idea what the problem is.
Did you put in a new STA508 when you put it all together? Or were you just testing the power supply? Also you can get it from Mouser... its a STA50813TR
Be careful not to short anything because that PWM will go kapow. Take it slow and methodical.