[AllanG]

I have quite a lot of experience constructing circuit boards which contain sensitive (usually ic) devices that require careful handling and use. Having been involved with the WeatherDuino project since 2014, I have read carefully the notes, guidance and instructions that Werk_AG has posted as I've been building the several boards that I have so far.

Even so, I've recently made a very stupid, basic mistake that we have been warned about, and which has destroyed my PLUS rx board.

The warning, which has been very clear for a long time is basically that you must NEVER risk having power applied to the PLUS rx board via the USB connector only. 

I chose to try achieving that by remembering to connect my board to the computer only after switching on the external 9v supply and also disconnecting from the computer before switching off the 9v supply. Although I tried, unfortunately I didn't succeed and the result was strange intermittent behaviour and the eventual complete failure of the board. As I had been using this board for testing, it was not running continually so was regularly powered on and off as well as connected and disconnected from the computer. Although I tried my best to remember the sequence, I've obviously got it wrong at least once - which maybe all it takes to cause damage.

The thought has occurred to me that there are also other ways in which this situation might arise. The most obvious is a scenario where the PLUS rx is properly connected to external 9v power via the mains supply while the attached computer has battery power available or is fed by an Uninterruptable Power Supply of some kind. In the event of a mains power failure - or failure of the 9v supply, the USB connector will be supplying power to the board while there is NO external power available - the board-killer situation!!

The only solution which is guaranteed to prevent the risk of damage, either accidentally as above or through a moment's carelessness as in my case, is to REMOVE THE DIODE on the Meduino as strongly recommended by Werk_AG in post 3 here:

http://www.meteocercal.info/forum/Thread...uick-Guide  

I'm off to do that myself right now while I wait for a replacement board to arrive...

Apologies for "shouting" in places but I'm so annoyed with myself!! I'm sure you will be equally annoyed if you too make such a silly mistake so please, do that modification now!!

Allan.

[Palmyweather]

Hi Allan

Sorry to hear that you have lost your Pro2 Plus board.

What do you think failed on the board that caused its death? Do you think that the component/s that failed are replaceable? Are they only components on the Pro2 Plus board that failed, or are the extra components that need to be purchased also potentially damaged (EG: LCD screen, temperature/pressure sensor, RTC, receiver/transmitter modules... etc)?

Regards,
PalmyWeather

[AllanG]

Hi PalmyWeather.

I sent my dead board to Werk_AG for an Autopsy and I'm sure he'll give the full details. But as I understand it....

In my case the 74AHC244 device had failed, almost certainly because voltage had been applied to an input while the chip itself was not powered - the result of "stray" power from the USB connection. Apparently similar damage can also be caused to the flash memory chip and WiFi module although in the case of my board, that wasn't the case fortunately. 

I think it's unlikely any of the peripheral components are damaged although I can't be sure until I've tested them on a replacement board. They *should* be ok, the PLUS board itself wasn't killed instantly, it died a slow death...   It seems the first symptoms appeared here:

http://www.meteocercal.info/forum/Thread...on-PLUS-rx

In my last post I thought my "intermittent problem" had been solved or gone away, as intermittents sometimes do, but a few days after that last post the symptoms reappeared and in another day or so the board had died completely.

I hope that helps but I'm sure the Coroner, Werk_AG , will be along to fill in any bits I've missed and to repeat the importance of making sure there's absolutely no chance of unwanted power from the USB!!

Regards,

Allan.

[werk_ag]

... Werk_AG , will be along to fill in any bits I've missed and to repeat the importance of making sure there's absolutely no chance of unwanted power from the USB!!

Hi AllanG,

I think you haven't missed any bits. The only and effective solution which covers all possible situations, is removing the diode referred here. Doing it totally prevents the board from being powered through the USB port.

[clubjoker]

Thanks for the warning and explanation of what to do.

It sounds like removing the diode from the Meduino is essential, otherwise it's just a matter of time before it's fried.

[qldbureau]

Thanks everyone for the heads up. Modification performed today.

[f4aii]

i made the same mistake....
now i must change the IC on the board for revival the board.

[Barrow4491]

Hi
Thanks for the warning, I have removed the diode as suggested even though my system is powered by a 12 v SLA Battery kept charged from the mains which supplies a pair of 5 volt (to power the raspberry Pi) and 9 volt (RX pro plus board) DC /DC converters.
Regards
Jim
PS Since I have resolved my transmitter RF issues the system has been extremely reliable with the only down time being for software updates