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IceTube Clock display goes out after a minute
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Re: IceTube Clock display goes out after a minute

by adafruit on Thu Jul 08, 2010 7:24 pm

erikd wrote:No, not the boost MOSFET I'm talking about the VFDPWR transistor Q3. I am suggesting it is a design flaw. I just measured 70mA from the base of that transistor to pin 5 of ATMega168 chip. The datasheet for the ATMega168 list a max current for the I/O pins at 40mA.


can you verify for me the part number on the transistor?

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Re: IceTube Clock display goes out after a minute

by adafruit on Thu Jul 08, 2010 7:25 pm

stinkbutt wrote:Oh. Well, then perhaps you've accidentally bridged the pins on the Q3 (VFDPWR) transistor. Can you check those three pins from above? They look fine from below, but they might be bridged on the top side of the board. This behavior is consistent with all three pins being shorted, I would imagine...


hiya - thanks for trying to help out - please sit this one out for awhile we help erik though, thanks!

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Re: IceTube Clock display goes out after a minute

by erikd on Thu Jul 08, 2010 8:06 pm

Part verified PN2907. I lifted pin 5 on the ATMega168 and jumpered emitter to collector of Q3. The clock has been running for a while now, much longer then ever. The fuse is no longer warm and the ATMega168 is only warm now, not hot. You might want to rework this area of the design by incorporating the proper bias resister for the transistor. I haven't crunched the numbers but a JFET such as the 2N7000 in place of the transistor might work as a drop in replacement fix.
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Re: IceTube Clock display goes out after a minute

by adafruit on Thu Jul 08, 2010 9:33 pm

we havent had this problem before - the pins are current limited, but agree with your assessment and are looking for a pfet replacement. if you would like us to send you one, please email support@adafruit - it may take a week or two for the parts to get to us and then send to you. in the meantime you can remove the part and tie the collector to the emitter and remove the coin cell :)

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Re: IceTube Clock display goes out after a minute

by erikd on Fri Jul 09, 2010 8:57 am

From perusing the forums I did see another user with a problem with pin 5 of the ATMega only his pin was non-functional and stuck high.

viewtopic.php?f=41&t=14074

If a failure mode of this pin is to stay low no one would notice other then shortened battery life on battery backup. Mine happened to sink a bunch of current which is how I found the issue. Thanks, I would like the replacement part when you choose one. I would like another ATMega as well. It does still get warm which I wouldn't expect either. Getting that warm it wouldn't run very long on a 3v coin battery..
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Re: IceTube Clock display goes out after a minute

by erikd on Fri Jul 09, 2010 2:10 pm

BTW, What is the target high voltage for full brightness (90%) with tube installed?
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Re: IceTube Clock display goes out after a minute

by adafruit on Fri Jul 09, 2010 9:29 pm

it varies by tube, but as high as 60V, probably realistically between 40 and 50

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Re: IceTube Clock display goes out after a minute

by erikd on Fri Jul 09, 2010 11:03 pm

Ok, thanks. I only get 29volts. I'll have to look into this.
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Re: IceTube Clock display goes out after a minute

by pstemari on Sun Jul 11, 2010 11:02 pm

It's an interesting question because the base of Q3 is going to want to sit a diode drop below VCC, i.e. 4.4V. There's nothing special about Q3, just a 2N3406/2N2907 general purpose transistor. I don't think the ATMega has any current limiting built into the outputs.
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