I think I’ve created a short to a ground plane... Help!

Thread Starter

number49

Joined Dec 5, 2018
12
Hi all,

Please forgive me my ignorance of this is ridiculously silly but I’m learning by doing and just need a little guidance with the following from people with more experience...

Trying to repair an amp from my car and think I have hit a snag. I had a damaged trace and pad so I followed guides on how to scrape off a little solder mask to expose copper and then remake a trace.

The problem is that when I was checking the resistance of my repair to an input trace for a voltage regulator I noticed it now gives continuity to ground pads in the same area of the pcb.

I assume this is a short and that in error I have exposed a copper ground trace or plane on a lower layer in the board and now connected the input trace directly to ground. Does this seem likely???

This image from underneath the pcb shows a large square which in hindsight looks to me like a ground plane (from what I can find by google) I’m hoping I’m wrong but could do with some help to confirm.

48E79922-5996-478C-B51C-EF0E0C7990E3.jpeg

If so, I assume I need to remove my repair, repair the solder mask I scraped off then use a different method to repair the input trace instead?

Any help greatly appreciated.

Thanks

Mike
 

danadak

Joined Mar 10, 2018
4,057
Is the regulator blown ? Can you lift the input leg on the package to
see if its the issue ?

What caused the initial damage ?

Regards, Dana.
 

Thread Starter

number49

Joined Dec 5, 2018
12
Hi Dana,

The regulator was faulty as the output voltages were fluctuating instead of being stable. Apparently it is common on this specific amp and others of similar spec. It is a DFN8. When I removed it a pad and small amount of the input trace came off with it as I don’t think I’d used enough heat to free it up properly.

I scraped a little solder mask off to copper where the trace was and have remade the 5v input trace but now it gives continuity to ground which is why I’m wondering if the copper is actually a ground plane or something as there’s no visible link to ground with the voltage regulator removed...
 

Thread Starter

number49

Joined Dec 5, 2018
12
This may be a silly question, but how do you know that the trace you repaired didn’t already have a connection to ground?
I thought that if there was a direct connection between 5v input and ground then that would be a short and would stop the circuit working, blow a fuse, damage components etc? Is this not the case?

Here is the circuit schematic for the regulator:

ED28410F-58D1-4DF2-B10E-E4F3D6852692.jpeg


I have circled the 5v input trace I repaired (note the capacitor that normally goes between the input and ground is removed while I repaired the trace so my understanding was that there’s no physical link to ground at this point). This is all new to me so I’m keen to learn if this isn’t the case.

Mike
 

Thread Starter

number49

Joined Dec 5, 2018
12
I thought that if there was a direct connection between 5v input and ground then that would be a short and would stop the circuit working, blow a fuse, damage components etc? Is this not the case?

Here is the circuit schematic for the regulator:

View attachment 168396


I have circled the 5v input trace I repaired (note the capacitor that normally goes between the input and ground is removed while I repaired the trace so my understanding was that there’s no physical link to ground at this point). This is all new to me so I’m keen to learn if this isn’t the case.

Mike


Here’s a photo as it is with the input capacitor and voltage regulator temporarily off:

View attachment 168398
 

Thread Starter

number49

Joined Dec 5, 2018
12
View attachment 168399

What I have marked as Gnd has continuity with what I have marked as 5v and also with the square pad which goes under the centre of the voltage regulator which I understand to be Gnd and also for dissipating heat.

Like I said above this is all new to me so please let me know if I am missing something or have an error in my understanding.

Thanks again for taking time to look.

Mike
 

Thread Starter

number49

Joined Dec 5, 2018
12
Just wondering if anyone can help with my original query about whether the copper I exposed is likely to be a ground plane/trace based on the fact my repair to the 5v input trace now has continuity with ground?

Am I missing something obvious or am I right that I have accidentally created a short to ground so need to remove my repair, reinsulate the exposed copper and remake the trace another way???

Any help appreciated as I really don’t want to make things worse :(
 
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