B&W A7 no power - PSU repair help please

[Kumra]

Hi,

I have a B&W A7 audio system that no longer powers on. I have pulled the unit apart and inspected for damage to the Power Supply and there are no visible burn marks or anything that I can see. SMPS70_v1.1 is the part number.
However I can see that these seem to fail semi regularly.

I have tested it a little bit using my multimeter and I can see a fluctuating 5v (jumps around like 3.9-4.9V) line going from the PSU to the main PCB. I have seen that if you jump this 5v to another pin of the connector on the PSU that it should turn on the amp, but this does nothing at all. i've tested around the board and can see no obvious shorts to caps etc. But im not 100% up with how to test everything.

Any help would be greatly appreciated in regards to trying to diagnose and repair the issue.

PS. i'm slightly new at this. I've only repaired a few Laptop mainboards are this point.

I gave up trying to upload photos here, but here's a google drive link to them:
https://drive.google.com/file/d/13oT_SbxopDm4xs96cCSdk8mCatPitNQ-/view?usp=sharing https://drive.google.com/file/d/1kgr4Geg2tBNkzbN14-mWqnkPGgrYG5lD/view?usp=sharing

 

[Kumra]

Sorry it wont let me upload photos at the moment. I'll keep trying

 

[Bluejets]

resize photos to an acceptable size.

 

[Kumra]

resize photos to an acceptable size.

Hi There, what are the restrictions for photos? I couldn't find them

 

[Martaine2005]

Frustratingly, the forum doesn’t indicate size limits, just an error!.
Guaranteed sizes seem to be approx 300KB.
It would be nice if the forum owners actually replaced the ‘error’ message with a reason. “File too large, resize to …”
But I guess that would be too easy?.

Martin

 

[Kumra]

There we go

 

[Erstwhile]

Hi,

I have a B&W A7 audio system that no longer powers on. I have pulled the unit apart and inspected for damage to the Power Supply and there are no visible burn marks or anything that I can see. SMPS70_v1.1 is the part number.
However I can see that these seem to fail semi regularly.

I have tested it a little bit using my multimeter and I can see a fluctuating 5v (jumps around like 3.9-4.9V) line going from the PSU to the main PCB. I have seen that if you jump this 5v to another pin of the connector on the PSU that it should turn on the amp, but this does nothing at all. i've tested around the board and can see no obvious shorts to caps etc. But im not 100% up with how to test everything.

Any help would be greatly appreciated in regards to trying to diagnose and repair the issue.

PS. i'm slightly new at this. I've only repaired a few Laptop mainboards are this point.

I gave up trying to upload photos here, but here's a google drive link to them:
https://drive.google.com/file/d/13oT_SbxopDm4xs96cCSdk8mCatPitNQ-/view?usp=sharing https://drive.google.com/file/d/1kgr4Geg2tBNkzbN14-mWqnkPGgrYG5lD/view?usp=sharing

Can you substitute the power supply with a bench supply to see if the system works that way?
Do you know what voltage the PSU is supposed to be putting out?
I'm not sure what you meant by "jump this 5v to another pin of the connector on the PSU that it should turn on the amp,"
I suspect that is a way to signaling "power good" to the PSU, but that is just a guess.

As for "there are no visible burn marks or anything that I can see" is not a rare occurrence with a SMPS, but they are hard on their electrolytics and switching transistor(s).

 

[Harald Kapp]

It would be nice if the forum owners actually replaced the ‘error’ message with a reason. “File too large, resize to …”

Totally agree. Hasn't happened for years despite repeated requests.
Also 300 kB is a bit anachronistic, isn't it?