Ack! Connected my flasher board backwards! chips got toasty!

Matt1982 · Post by **Matt1982** » Sat Apr 21, 2012 8:54 am

Terrible. I connected my custom made flasher board with a reverse polarity of 6v supplied via 4 AA.

The chips got warm. I thought it was all over, but when I connected it via the correct polarity, it now works.

Is this board ready and waiting to fail now? Thoughts? This board is to be permanently placed in a 1:350 model.

Mr. Engineer · Post by **Mr. Engineer** » Mon Apr 23, 2012 7:21 pm

Well, is there a circuit diagram or any (clear, enlarged) pictures you can show us? I am curious how it can survive a reverse polarity.

Matt1982 · Post by **Matt1982** » Tue Apr 24, 2012 2:51 pm

It is three 555 timers and one 4017 decade counter. The outputs are notated through darlington pairs.

Mr. Engineer · Post by **Mr. Engineer** » Thu Apr 26, 2012 3:25 am

Sorry for the delay.

555 and 4017, eh?

Anyway, I know that the 555 has a reverse polarity of about 5 volts but I am not sure about the 4017. I am not so sure about your shops over there, but since (I have to assume) these chips would be using their respective IC sockets, just to be on the safe side, go out, buy the three replacement 555 and 4017 (be careful about static for this little CMOS) and plonk them on to the board.

I would go this way rather than have doubts when the model is sealed. But then, that's just me since these chips are very cheap from where I live.

But I cannot say the same for the Darlington pairs. you might want to look it up their respective datasheets.

Matt1982 · Post by **Matt1982** » Thu Apr 26, 2012 4:43 pm

I replaced the chips, The circuit has run for 16 hours without any problems. Can I assume it's safe?

Mr. Engineer · Post by **Mr. Engineer** » Thu Apr 26, 2012 6:51 pm

The burn-in test proves that the circuit, esp the Darlignton pair is OK which means, it should be alright to out into the model.

But just be careful with it, OK? Check and re-check every step to make sure the circuit is A-OK.

Its PITA but its the surest way to defeat Murphy's Law which is the most powerful just after the last drop of glue dries...