Ice Tube Clock Q3 FET install and some assembly Tips

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filter4ever
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by filter4ever »

I am having the same problem. My clock works fine, but it does not keep time when the power is off. I checked the "batt sense" voltage divider - OK, the schottkey diode D4 (backwards - OK) 2.94 on VCC (Power Off). Diode OK. Killed my last battery in 2 days. When I power it back on, the display flashes, but it is the same time the power went off (the time doesn't keep running). I don't understand, on the last same exact kit I built 4 year ago it worked like a charm. I will check the FET on the other one I gave as a gift, my guess is it's different. This one has got the dot going to the rounded silkscreen, and the text towards the 22 ohm resistor. I measure .5v on the pin closest to the edge with the power off. I was thinking of trying to find the original FET from my first kit and replacing it. Any ideas?

filter4ever
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by filter4ever »

Sweet, I fixed it! You were right, the FET was backwards. In the instructions, it says to face the text towards R3 if it's on the curved side. This seemed a bit funny why a manufacture would change the Source, Drain, and Gate pins, the entire 'mold' for the silicon, just to change the print. When I removed the FET, I measured a 1V drop (1.5v) across the battery, even with the power connected. I thought they had burned me by giving me a dead battery, but it was new in the pack, so I bought 2 more. I left one in for 4 hr, it's down to 2.6V now. Just put a fresh one after changing the FET, only a 100mv or so drop with the power disconnected, and it keeps time, however it would be cool if the battery was a bit larger and it could ring the alarm when the power was disconnected, since that's usually the problem. The power goes out you wake up for school or work late. I wish it showed the S, G, D, on the schematic. Perhaps an update to the schematic, or printing "S-G-D" on the silkscreen, will help others on the future? The datasheet is easy to find for this FET, but including it in the files would help beginners. Thanks for all your help! 8)

filter4ever
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by filter4ever »

Sorry, I meant I measured a 1.5v drop across the battery when the FET was in BACKWARDS. I think 2.9 something on the VCC with it removed, rather than .5v. Obviously something was shorted out with this FET in with the curved side facing the resistor. Killed the battery fast.

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phild13
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by phild13 »

Glad you got it working properly.

If the FET is installed backwards, it will still conduct current when it is not supposed to and the battery will try to power not only the processor chip (IC1), but also try to power the filament of the tube and power the VFD (IC2) chip. In other words, the two things Q3 was designed to disconnect. Since the battery cannot supply much current for very long it is drained. I agree that unless there are some counterfeit FET's in the supply chain, then it makes no sense for a manufacture to swap the source and drain just to print text on a different side. I would think the writing on the curved side is more of a assembly line decision.

The original schematic for the clock had a PNP transistor as Q3 without a base resistor. This PNP transistor was later changed to a FET for various reasons. Your kit 4 years ago may have had a regular PNP transistor (2N2907 which is now obsolete), or the FET's may not have had the writing on the curved side, or the assembly instructions may not have directed one to turn the FET around.

Of the FET datasheets I have looked at for Q3, they indicate that a p-channel TO92 packaged FET would be installed in an orientation matching the silkscreen. The main boards silkscreen for Q3 is then actually correct in orientation in relation to the schematic for both a PNP transistor and a P-channel FET, it is just (in my opinion) the added assembly instructions to turn the FET around backwards if the text is on the curved side, are incorrect.

Some may be thinking to just replace the FET with a PNP transistor. That is also a solution, but be aware that you cannot directly replace the FET with a PNP transistor. You would have to add a Base resistor like Russell 27 explains here:
http://forums.adafruit.com/viewtopic.php?f=41&t=43908 I think you can get suitable parts from Radio Shack.
...however it would be cool if the battery was a bit larger and it could ring the alarm when the power was disconnected, since that's usually the problem. The power goes out you wake up for school or work late.
An alternative icetube clock firmware, the xmas-icetube by jarchie, will ring the alarm even if the power is out and the clock is on battery so you never have to worry about the clock not waking you due to a power outage. The xmas-icetube firmware does require a larger processor chip (Atmega 328). I don't know if the alarm during power outage functionality could be worked into the existing ATmega 168 (the default icetube clock firmware) code as I don't know how much space is left for additional code. I do think that would be an incredibly handy feature to have in the base code.

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jarchie
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by jarchie »

I don't know if the alarm during power outage functionality could be worked into the existing ATmega 168 (the default icetube clock firmware) code as I don't know how much space is left for additional code.
There's enough room, although the programming aspect is a bit tricky. Older versions of xmas-icetube fit on the ATmega168v, and the sleep code worked reliably at that point.

adafruit
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by adafruit »

The silkscreen, as far as we know, is correct. Tutorial section has been updated - every few months someone adamantly complains that the instructions are wrong and that D and S are swapped on their P-FET and they're a 30-year EE and know what they're doing and has some tests to prove it. So we update the instructions. We've done this a few times now! :) We checked against the datasheet and the PCB and Drain is near the edge of the PCB, Source is closer to the middle.
It could be that we got a batch of swapped-package transistors a while ago, its hard to know for sure since they filter in and out of the forums every once in a while and some people can't tell if its fixed or not.

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motocoder
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by motocoder »

adafruit wrote:The silkscreen, as far as we know, is correct. Tutorial section has been updated - every few months someone adamantly complains that the instructions are wrong and that D and S are swapped on their P-FET and they're a 30-year EE and know what they're doing and has some tests to prove it. So we update the instructions. We've done this a few times now! :) We checked against the datasheet and the PCB and Drain is near the edge of the PCB, Source is closer to the middle.
It could be that we got a batch of swapped-package transistors a while ago, its hard to know for sure since they filter in and out of the forums every once in a while and some people can't tell if its fixed or not.
Yes, I'm the customer that complained (via your support form) yesterday, and I see that you updated the instructions page already. However, no one has replied to me about sending me a replacement for the ruined FET. When will that happen? My son and I spent most of the day yesterday assembling the clock (his first time soldering, so it went slow), and he's really eager to have his Christmas present up and fully operational.

BTW - maybe you should source an alternate part given these problems - or break out the transistor tester and go through your inventory...

Thanks

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jarchie
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by jarchie »

motocoder wrote:BTW - maybe you should source an alternate part given these problems - or break out the transistor tester and go through your inventory...
Whenever I see people building an Ice Tube Clock, I suggest or give them a ZVP2110A to use for Q3, so that might be one possibility.

Switching to a better FET would solve two other issues as well. First, the FET included in the kit does not turn on fully, which on some tubes causes the final and (less commonly) initial digit to appear dimmer than the others. It also seems to accelerate cathode poisoning on the 3rd and 6th digits which are unused when displaying time. Second, although I have not observed this behavior in-person, others have reported time not being kept during sleep due to the kit-included FET failing to turn off fully (and I believe those reports).

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motocoder
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by motocoder »

Whenever I see people building an Ice Tube Clock, I suggest or give them a ZVP2110A to use for Q3, so that might be one possibility.
John - thanks for the advice. I think I'll just order a few ZVP2110A from DigiKey and use one of those for a replacement. It seems like Adafruit isn't responding to my customer service request for a replacement. I'll give them the benefit of the doubt and assume, like most retailers, they're swamped with post-holiday customer service requests. And in any case, it's always nice to have a few small p-channel enhancement mode FETs on hand - unlike the larger power mosfets, they seem to be hard to find locally.

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adafruit_support_bill
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by adafruit_support_bill »

Yes, I'm the customer that complained (via your support form) yesterday
It seems like Adafruit isn't responding to my customer service request for a replacement.
@motocoder - This is your third post with this user name. I do not see where we established that you had a defective MOSFET. If you posted this issue under a different name, please post a link to the relevant thread.

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phild13
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by phild13 »

Simply installing the FET backwards on the clock board will not ruin it. Excessive heat from soldering/desoldering it, and static will, so use good practices there. I agree with Jarchie that the FET specified does not seem (as reported in the forum) to necessarily work well with all kits and a better choice of FET would be the ZVP2110A FET.
As an alternative to a FET you can use parts from Radio Shack as Russel 27 explained how to do if you have a store nearby to replace the FET with a transistor/resistor combo
http://forums.adafruit.com/viewtopic.ph ... or#p219063

Good update on the kit instructions Bill, so pass thanks along to whoever is responsible.

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motocoder
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by motocoder »

adafruit_support_bill wrote:
Yes, I'm the customer that complained (via your support form) yesterday
It seems like Adafruit isn't responding to my customer service request for a replacement.
@motocoder - This is your third post with this user name. I do not see where we established that you had a defective MOSFET. If you posted this issue under a different name, please post a link to the relevant thread.
I didn't post that here, but rather with the support form on the "Contact Us" page. This is the method I used previously when you sent me an unprogrammed "Arduino bootloader-programmed chip", and before that when you sent me a Raspberry Pi camera mount that was broken. It worked both times before, so I followed that same approach this time. It is order # 382950 in case that helps.

I had some difficulty desoldering the MOSFET, and ended up clipping the leads, which I then realized were too short to re-insert in the board. Realizing I was probably screwed at this point, I nevertheless went ahead and soldered some extension leads on the MOSFET. This is what is in the board now, and although the display lights up fine, he MOSFET is not switching off at all - it's basically a resistor at this point. I assume it got cooked with the repeated soldering and desoldering. The back-up battery is drained within seconds as before (which reminds me, that needs to be replaced as well).

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adafruit_support_bill
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by adafruit_support_bill »

I didn't post that here, but rather with the support form on the "Contact Us" page.
All technical support questions should be posted here in the forums. If our support engineers determine that a replacement was warranted we will refer you to customer support.

If yours was installed backward due to an error in the instructions, please contact [email protected] with a link to this thread for a replacement.

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motocoder
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by motocoder »

If yours was installed backward due to an error in the instructions, please contact [email protected] with a link to this thread for a replacement.
Ok, thank you for clarifying that. Indeed, mine was installed backwards only because of the error in the instructions. However, at this point I've already placed an order with Digikey for a replacement MOSFET, so I don't see any benefit in asking Adafruit to incur the expense of sending me one. I'll pick up a replacement battery at the local drugstore.

Thanks

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motocoder
 
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Re: Ice Tube Clock Q3 FET install and some assembly Tips

Post by motocoder »

Whenever I see people building an Ice Tube Clock, I suggest or give them a ZVP2110A to use for Q3, so that might be one possibility.
John - thanks again for your help. The ZVP2110A came in from Digikey today, and after double-checking the pinout, my son installed the MOSFET, consistent with the part outline on the silk screen. The voltage on the MOSFET drain when running on battery was 0.02V, and the battery backup feature is working great.

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