Ice tube clock - Getting started with the parts

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pesco
 
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Re: Ice tube clock - Getting started with the parts

Post by pesco »

Hi, I am experiencing the same problem with the battery. The clock works (and is wonderful!) but does not keep running when disconnected from main power. It's obviously not a big problem, but I want to fix it!

I measured 2.84V on the lithium cell that was shipped with the kit and figure that should be enough...

At first, I got only 2.5V between ground and the battery holder, so I checked the connections. It seems that flow from the solder had covered the blob that forms the ground terminal below the holder. I scratched it free with a small screwdriver and cleaned it with some alcohol on a cloth.

Now I measure the full 2.84V between ground (backplate of the regulator) and the top of the battery holder. However, the problem persists.

I double-checked the look of my solder joints, cap orientations, diode orientations, and that I had placed the resistors for the divider correctly. It all looks good but apparently I am still missing something.

Do you have any tips where else to look?

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adafruit_support_bill
 
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Re: Ice tube clock - Getting started with the parts

Post by adafruit_support_bill »

@pesco. Post some photos of the front and back of the boards & we'll check your assembly.

pesco
 
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Re: Ice tube clock - Getting started with the parts

Post by pesco »

Here are the pictures. I apologize for the suboptimal quality, I hope it is good enough to see what's important.

I measured the pins of the Atmega with the battery connected; no 9V, no VFD. Here are the non-zero values:

1 (RST): 2.47V
3 (?): 2.63V
5 (VFDPWR): 2.63V
7 (VCC): 2.64V
9 (XTAL1): 0.55V
10 (XTAL2): 0.38V
13 (BATTSNS): 0.7V
20 (AVCC): 2.64V
21 (AREF): 2.64V
27 (?): 2.64V

I also measured the pins of Q3 and strangely, they all show positive voltage. Isn't it supposed to shut off when VFDPWR is high?

TOP (near edge of board): 2.1V; also behind R3 and on the corresponding pin of the MAX
MIDDLE: 2.64V
BOTTOM: 2.64V

Because of this I made a close-up of Q3 to show that there are no shorts. One joint on the back looks pretty close to another one but I verified with the multimeter that they are not connected.
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phild13
 
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Re: Ice tube clock - Getting started with the parts

Post by phild13 »

Given the voltages you measured on Q3 while on battery, I think that Q3 is in backwards. See the link below for more info.

With no 9 volts there should not be any voltage on the pin closest to the edge of the board. Since there is voltage on this pin (2.1 is same as what I measured), that means the body diode of the fet is conducting feeding voltage all the time to the vfd chip and the tube bias pin. The difference between voltages on the top pin and the bottom pin is probably because of the forward voltage drop of the body diode. Being in backwards won't hurt it but it can't do the job it was designed to do which is to remove battery power from the vfd (Max) chip and the tube bias pin (R3) when the clock looses normal power.

Even though it is installed according to instructions, try taking it out, and turn it around so the curved side matches the silk screened outline for Q3 and give that a try. Be careful not to overheat Q3 if you decide to desolder it and not clip the leds and clean the holes.

The bottom pin should have battery voltage on it.
The top pin closest to the board edge should not have voltage on it.


See for more info: http://www.adafruit.com/forums/viewtopi ... 41&t=43209

pesco
 
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Re: Ice tube clock - Getting started with the parts

Post by pesco »

Indeed! The thought of looking up the transistor's datasheet had crossed my mind, but I somehow couldn't imagine that part being wrong.

Unsoldered and flipped it, now it's working as it should. Thanks a lot!

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phild13
 
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Re: Ice tube clock - Getting started with the parts

Post by phild13 »

Your welcome!

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jarchie
 
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Re: Ice tube clock - Getting started with the parts

Post by jarchie »

jarchie wrote:On another note, if Adafruit does not want the possibly defective boards returned, Alex is willing to send me his board, as I'm really curious what the underlying issue is. If things work out and I get Alex's board, I will post whatever I discover.
I just wanted to write that I have not been able to get my hands on one of these possibly defective boards. Perhaps Alex has been too busy to assemble his new kit...

Anyhow, I just wanted to post that if I knew anything that might help, I would have shared that information here.

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