Shorted PCB pads (SW5) and Short to GND on the 3.3 rail

[michalism]

Hello
First of all, congratulations on your great product and thumbs up for the great forum!! really educational!!

I have found that 2 pins of the SW5 switch are shorted on the board (and shorted to ground) and also the 3.3V rail is shorted. SW4, SW6 and SW7 tested and they are OK. Is this possible? How can this happen? Do I have a faulty board? Can the 3.3V rail be shorted because of the SW5 pads being shorted?

Story and troubleshooting steps:
When I assembled the unit, I measured 3.3 V on TP22, and shorted JP4. After connecting the power supply, I only got a white screen and I also noticed that the LED is not blinking.
I removed the screen to take measurements from various points, but then I noticed that U5 gets extremely hot 3-4 seconds after I connect the power (9V) to the board.
I have disconnected JP4 and powering up the unit again, U5 stayed cool.

I measured a short between the 3.3 trail and the ground, but after the power supply circuit. Various voltages are wrong, but I guess this is normal since the 3.3 rail is not working properly. Q1 and Q2 are checked and they are OK, but I also used new ones just in case. the result is still the same.
I checked around the microprocessor and I found that pins 1, 8, 9, 23, 24, 27,28, 35, 36, 47 and 48, all seem to be connected to ground. I suppose this is not normal, and so I removed C16, C17 & C18 from the circuit but the short was still there. Also if I check the pads for C16, C17, C18, they are also shorted!

Any help would be much appreciated!

thank you
Michalis

[jye1]

Can you post photos of the board (both sides) ?

[michalism]

Hello

here are the pictures.

Thank you
Michalis

[michalism]

Hello.
Any ideas? Did you have a chance to check the photos?
Thank you
Michalis

[jye1]

On the PCB most the empty space where there are no traces is covered with copper and the copper is connected to GND. This means most pads are surrounded by GND with a very small gap. Normally the GND copper is isolated by paint at top. If somehow the paint around a pad is damaged bridge (short) is easy to form by solder. For your case +3.3V is shorted to GND. The bridge said above could be a cause. So it is suggested to clear eacj pad that is connected to +3.3V to make sure there are no bridges (To do this add a little flux at a pad and let iron stay on it for a little while).

Another cause for the issue is shorts inside the chip U1. To verify the chip needs to be removed. This is hard to do without proper tools and adequate skills.

It is also possible due to the PCB itself. But this possibility is very low since the board has gone through first the chip programming and then testing. Hard fault of PCB won't pass both.

[michalism]

Hello

I have managed to remove the chip and it is shorted. this is the root of the problem.
how can i get a new chip?

thank you

[jye1]

Please contact JYETech at jyetech@gmail.com with photos of your board and purchase proof.

[michalism]

Hello

I have contacted jyetech@gmail.com but I did not get a responce.
can you please help?

thank you