ground issues in my double side pcbs

[sp2012]

Hello to all,

I did a double side PCB for sim900d.In this i am facing the following issues.

1.If i keep the board in my hand its working but i kept in table or floor its not working?

2.one or two day continuously working without any issues and then its not working.After some days again its working.
without restart the power.

3.I am using LM2576 Adj power supply.If i remove power supply it takes 3 to 5 seconds to discharge the voltage.


These are the major issues i am facing.


Thanks In advance........

 

[d3javu]

Are you able to show your schematic/pcb? Not easy to guess the problem by just reading like this.

 

[jayakrishnanj]

Like d3javu said

we need schematic to know analyse your problem,

or

my assumption is your board may have poor soldering or Grounding issue

 

[sp2012]

Hi jayakrishnanj,

Thanks for your reply.

Please give your mail id i will share my schematics and pcb layout also.


Thanks.

 

[d3javu]

Hi, just glanced through the schematic... i didn't notice any issue except for one, why did you use adjustable power regulator for this type of circuit? how stable is it?

On the pcb side, have you checked all the compliance? The ground pours.. separation of analog/digital.. stitches..? Since it works on and off.. you really want to double check your pcb and all the traces for any anomalies or other issues.

 

[Mattylad]

Have you actually got a ground pour on the board?
Or is it just a copper pour that's not connected to ground?
A floating pour may well be the issue going off your description, while it's in your hand it's being grounded via you & when on the table it's not.

Or it could be because you have 3 ground nets Earth, GND and PGND and I cannot see any connection between them in the schematic and you have some parts referenced to Earth yet other parts of the same circuitry reference to PGND etc.

Take IC2 where the 3.3v is generated from the 4v (I assume) - it references to Earth.
The flash IC is powered by 3v3 yet it's return is via PGND, as is L8, looking atthe other IC's they doo are supplied by 3.3\4v but return via PGND.
C11/C12 - I assume decoupling caps for IC4 (main processor ?) are referenced to PGND yet IC4 has a GROUND return so they will be ineffective.

So it could be you have split grounds that are not connected anywhere and when your holding the board you connect them (possibly via capacitance) and then when on the desk they are separate again.
Can you go through the whole circuit and review the grounding & return paths?

By the way, there are plenty of free PDF generators you can get that do not slap big watermarks across the output, like PDF995 - I like this one as I can edit, join, split pdf's also.

 

[Surendhar M]

Connect a co-axial cable along with an antenna on the GSM module to increase the signal strength. The co-axial cable has to connect properly with ground. Pads for these will be provided on the backside of the module. I think thats the reason the board is not working when you keeping it on table or floor or even after 2 days. Hope it solves ur problem.