TheBackShed.com

Forum Index : Microcontroller and PC projects : I seem to have killed an F4

Author

Message

lizby
Guru

Joined: 17/05/2016
Location: United States
Posts: 3378

Posted: 01:45pm 31 May 2021

Copy link to clipboard

Print this post

I was running it with a hat PCB which enabled an SPI ILI9341 (this had worked before). After OPTION LCDPANEL DISABLE, the LCD was lit, but OPTION LCDPANEL ILI9341, L, 87, 97, 33 didn't work as it had before (disco4now has explained that OPTION RESET is now required after OPTION LCDPANEL DISABLE).

While I was fiddling around trying to seek a solution, maybe after 5 minutes, the LCD panel went black, and I've been unable since then to get a com port or to reflash. When I plug in a usb volt & milliamp display, when I plug in the F4 USB cable, it shuts off.

Voltage measure on a 5V pin is less than 10 millivolts (so looks like a short). When I plug 5V & 0V (from and 18650 module) into the F4 com port (nothing attached), there is also 10mV on the other 5V pins. I've inspected the bare board with a magnifying glass, and there are no visible shorts and no visible sign of thermal distress.

I removed the battery and it read 2.99V.

Any ideas about what may have happened or what I might look for?

PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed

Volhout
Guru

Joined: 05/03/2018
Location: Netherlands
Posts: 5089

Posted: 01:53pm 31 May 2021

Copy link to clipboard

Print this post

Hi Lizby,

Most likely it is one of the ceramic capacitors that is connected directly between 5V (USB) and ground. I would remove them one by one, check, and place it back when no change.

If you have a very good multimeter, you can also connect the board to a 5V source that can deliver 1A, and then measure the voltage accross these capacitors (some 10mV or so). The one with the lowest voltage has the short.

PicomiteVGA PETSCII ROBOTS

bigmik

Guru

Joined: 20/06/2011
Location: Australia
Posts: 2950

Posted: 01:08am 01 Jun 2021

Copy link to clipboard

Print this post

Hi Lizby,

The first thing to determine is that the Short is actually on the 5V line.

Use your meter in ohms (or continuity) mode and check between the 5V and GND pins..

If it IS short there is not much that can cause it.

As far as I can see on the schematic of the F4 there are only 3 devices connected to 5V and GND..

C3, C5 and the AMS1117-3.3 VReg

C3 and C5 are located immediately to the right of the AMS1117-3.3

Remove one part at a time and check that the short is gone and replace the part with a new one if the short does disappear..

NOTE the schematic shows C5 as a polarised part but the one on my F4 is actually a ceramic non-polarised part.

MLCC capacitors due to their design often fail short and usually caused due to mechanical stress or damage.

If there is no short on the 5V line then check for a short on the 3v3 line but I suspect you would find there would be more than 10mV on the 5V line and the AMS1117-3.3 would be getting warm

Kind Regards.

Mick
Edited 2021-06-01 11:13 by bigmik

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

lizby
Guru

Joined: 17/05/2016
Location: United States
Posts: 3378

Posted: 02:12am 01 Jun 2021

Copy link to clipboard

Print this post

Thank you Volhout and Mick. Yes, there is a dead short between 5V and 0V.

I removed C5 and the short is gone. Now I have to see if I have a 106 10uF capacitor of that size in my limited surface mount collection.

Thank you very much. What a fine thing it is for this software person to be able to ask a question and get an answer from people who really know what they are talking about, with specific directions about how to check it out.

Is this a great forum or what?

~
Edited 2021-06-01 12:15 by lizby

PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed

disco4now

Guru

Joined: 18/12/2014
Location: Australia
Posts: 1003

Posted: 03:28am 01 Jun 2021

Copy link to clipboard

Print this post

lizby said (disco4now has explained that OPTION RESET is now required after OPTION LCDPANEL DISABLE)

Only before beta9 of the armmiteF4 firmware, fixed in beta9 and later.

Latest F4 Latest H7 FotS

lizby
Guru

Joined: 17/05/2016
Location: United States
Posts: 3378

Posted: 07:35pm 01 Jun 2021

Copy link to clipboard

Print this post

She lives!

Despite my pathetic surface mount soldering skills with tiny pieces, I managed to solder on a 10uF replacement for C5. And she boots to the MMBasic prompt.

Thanks again to Volhout and Mick--without your leading me by the hand I might have just shelved this F4 (I have 8 others).

Electronics repair--who knew it could still be done in this age of throwaway.

Lance

PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed

Mixtel90