Pro mini died after mod

Projects General Guidance
1

Hi looking for ideas on how to fix my pro mini's I have killed 2 of them by failed mods.
Both are low cost clones 5 volt versions

Unit 1 (I have most hope for fixing this one)
Tried to remove Pwr led, first by scratching the a trace which did not work, so I decided to desolder it.
Blink program was still running prior to desolder attempt.

Now that i removed the LED the blink program does not run, I tried to upload a program via USB programmer and the unit continuously blinks rapidly the same LED that blinks during a reset. The area to desolder is quite tight thus I am must have but messed up some nearby component. Perhaps I should add I 10K resistor between vcc and reset? NO LED blinking occurs if I just power the unit via VCC, The rapid blinking occurs when I connect it to the serial programmer.

Unit 2. Tried same mod, but hand was not steady and I managed to desolder the part next to the PWR LED also. it had part labeled 182 next to it that I slipped and desoldered.
This unit seems dead dead.

If you ask why, I am feeding 3-4.5 volts direct into the VCC pin via battery and trying to remove LED power drain to extend battery life, Trying to get approximately a year out of set of 3 AA's

Thanks in advance on any ideas to try and fix.

Also anybody out there sell low cost Pro Mini's with out a power LED. Removing it seems to be a common effort. I am 1 for 3 on the mods, Which is a bit embarrassing as it should be such a easy mod.

Highflier

2

You will get better at it! Just make sure that you use a small tip on the solder pencil.

At less than $2, I buy 5 at a time. I throw one away now and then, because of similar mistakes.

3

I did buy 5..... that only leaves me 3 LOL.

Highflier

4

highflier:
Also anybody out there sell low cost Pro Mini's with out a power LED. Removing it seems to be a common effort. I am 1 for 3 on the mods, Which is a bit embarrassing as it should be such a easy mod.

Removing the LED is not easy.

Remove the series resistor for the LED instead much easier.

5

I just rest the soldering iron, with a fair amount of solder on it, ontop of the LED. This melts the plastic away, enough so the glob of solder touches both sides of the LED at once. Same technique I use for resistors.

Another approach is to just take a knife or other scratchy thing to the LED itself - snapping off the plastic part will typically cause it to fail to open circuit.

6

Maybe try a breadboard with jumpers and a standalone micro. :slight_smile:

7

I prefer to remove the resistor instead of the LED. It is much easier to heat the whole thing and shunt it aside.

8

I like the idea of trying the resistor, Did anybody look at the link, cause i did not see where the resistor was.

I thought about the bare board idea, but that actually costs more, I think. Must be the cost delta between a dip part and a surface mount.

Highflier

9

Feeding 3-4.5V to a 5V board?
Why not get a 3.3V board?

10

I successfully disabled the LED on my pro-mini by inserting the blade of a small screwdriver under it and twisting until it broke (didnt take too much force)

3-4.5V along with disabling the LED sounds like a battery powered device that needs to last a long time.

11

highflier:
Did anybody look at the link, cause i did not see where the resistor was.

Do you really need a link to tell you where the resistor is ?

Use a multimeter to check, I did.

12

Nice idea for the power saving. If you are using an official arduino pro mini, you can find the resistor with label R6 on the board as the link:

However if it's a clone board, the resistor could be labelled differently. So the best way is checking by hand with a multimeter.

13

Just an update, I started comparing the basic pins VCC and ground on a good board to ones of the failing boards. On the pro mini there is 2 ground pins, (3 if you count the programmer connector). Well the 2 gnd pins on the board had N/C to each other. A small jumper wire later and poof. that board was fixed.

SO I checked the other board that I botched. It had the same issue, Plus the other part that I goofed on when my hand was not quite steady enough, After volt metering it I determined it was the power LED resistor (10k). Thus I left that spot alone, as there was no need for it with LED removed. I added the ground to ground wire and poof that one is up and running again.

Now while these units are slightly suspect, I have found no issues with them in my current circuit. plus since they both have had LED removed, I can use them in the ultra low power project that I am working on.

:slight_smile:

So other than the fact there is a jumper wire on the top of the board, all is great :slight_smile:

bwxd, R6 is the pin 13 LED which I could turn off via software, The LED that I was removing is LED1 and R11

Highflier