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12 years ago.
heat and voltage problem with display board
Hi I have the 1768 + rs display bord + 12v/1.2A + USB connected , all is new i trie to use the program of the cookbook without sucess Hello world Works well..
In fact , the Mbed card is very hot after just 5'( 50degC ?) and i havn't any voltage on all the 3.3 V pin The 5v on the display board is ok
The display bord keep black
Thank in advance for your help for this first trial
Eric, France
3 Answers
12 years ago.
the four vdd was cut and the GND and 3.3V are always shortcut.. no over common point, connectors are clean, over idea ?? i lift the 4 capa of the CPA-VDD-GND and no progress
two extreme way ;
burn the short circuit whith hight voltage..=no
repowered the PCA by and over way ...and disconnected the Mbed 3.3v of the display bord =yes i cut the 4 strips beetwin 3.3V bus and the capa and VDD-CPA replug the 4 capa euh 2 only in fact... replug a new line bus to the 3.3V-Mbed and the 4 VDD-CPA Cut the 3.3V-mbed pin to the DBoard..
Result, 10 led ok , no heat i have to reload the program test now
Just an over point to reconnect ; the two points marked with a "+" are to be polarised with the 3.3V (this two points aren't in short cut with the ground ! )
NOW ALL WORKS !!! incredible !!! Good day today !
Just somme fright to reconnect one of the PCA witch i had broken the vdd pin a zero .. but now , it seem ok ..
THANK YOU FOR YOUR HELP and your encouragement to go on head in this adventure !
I save my precious DB (Digital Board ) See you in my next adventure ...( my globale project is to connect the Mbed at some infra red barriere and to an Xbee to calcule/Display and save some chronometer times of a parralele slalom..)
posted by 16 Dec 2012
12 years ago.
if you remove the MBED, and just power it from usb, does it get hot ??
as mentiond above, if the board gets hot there could be a power rail short,
also if you power the DB, with no MBED, does it get hot ??
and most importantly where is the heat comming from.
bit difficult to tell withought thermal immaging camara,
or cryo spray.
Ceri
Hi, after control..there is a short circuit behing gnd and 3.3v pin on the display board DB with 12v = ok no heat Mbed with USB = ok , no heat The mbed supply the 3.3v at the DB in short circuit and the mbed heating...
Nothing appends wrongh on the db , certenly in the multi layer printed board...
So, i think my new db is goood for the bin...
bad day today..
posted by 11 Dec 2012
12 years ago.
I could not find a schematic of the board. What is the 3V3 used for, do you have a schematic? I assume it powers the i2c displaydriver. Perhaps that device is fried, but you may be able to replace it and repair the board.
Hi , I'have find that http://mbed.org/cookbook/PCA9635-I2C-IO-Expander insue of http://docs-europe.electrocomponents.com/webdocs/10fc/0900766b810fce00.pdf Look at http://mbed.org/media/uploads/d_worrall/_scaled_pca9635_pinout.jpg Where is the Ground ? That is Vss and VDD ,is one off it is the 3.3V ?, which ?
The difficulty to repair is that i can't check the 3.3V because GND is every where ! i can't unplugged all the CMS !! And the PCb is multi layer ....
Eric
posted by 12 Dec 2012Vss is gnd, Vdd is connected to 3V3. I expect that the board has multiple PCA9635 devices, probably 3, one per 2 displays. Depending on the boardtracks layout, you could try cut the Vdd wire to the PC9635s one by one and measure for shorts. There may also be other components on Vdd that cause the short (a protection diode or capacitor).
posted by 12 Dec 2012Thanks, Stupid question in fact for VSS-VDD, this is on my own schema to the Mbed-PCA .. there are 4 PCA , 1 dedicate for the 10 extra led Ok i'll try to unsold the 4 VDD, 1 by 1 but not tomorrow See you later Eric
posted by 12 Dec 2012now done , the four vdd was cut and the GND and 3.3V are always shortcut.. no over common point, connectors are clean, over idea ??
two extreme way ;
- burn the short circuit whith hight voltage..
- repowered the PCA by and over way ...and disconnected the Mbed 3.3v of the display bord
Please explain in more detail how the boards and powersupply are wired up.
When the mbed gets hot and the 3V3 output (pin 40) does not have any voltage then it is likely shorted to gnd or worse to 5V or 12V and the 3V3 onboard regulator might be fried.
Note that you should not connect the 12V to mbed Vin (pin 2). That voltage will generally cause too much dissipation in the mbed onboard regulators.
posted by Wim Huiskamp 10 Dec 2012Hi Wim and thanks( sorry for yesterday , i have see 0 respons and i haven't the habit of this type of "forum" )
You can see the type of mount here https://mbed.org/cookbook/RS-Display-Board the display board contain a 7805 to convert the 12VCC main power to powered the 1768 The Mbed is plugged on to the display board in the right direction ( usb and led easy to align to the DisplayBord DB) I had only measured the voltage on the DB ..( because i'm beginner with Mbed..) Note ; the led of Mbed light-on when it's unplugged of DB ( just plugged at USB ) and it's light-off when it's plugged at DB, and..It's light on when the DB is powered by 12v .
posted by k eric 11 Dec 2012