Consequences of C8, C9 mis-orientation

[kevinsworld]

OK.. like an idiot I mis-oriented the C8, C9 20pf Capacitors by 90 degrees. Does this mean they are blown if so? I was debugging my clock and the tube was only lighting up partial letters. I started checking voltages and ~most checked out as follows but then I discovered I messed up on these capacitors... not sure I will be able to pull them without destroying them and even then will they still be good? I'm hoping this was the problem but I won't know until they are fixed.

So my voltages checked out as follows in this mis-orientation.

7805 - without tube
Pin 1 - 8.71
Pin 3 - 4.99

Boost Converter Test test to diode D3 (striped end), with VFD chip in.

47.5 volts (this is with VFD chip installed, so is this a problem since it says it should read 14-16V with the VFD installed, maybe a consequence of the C8, C9 mess-up)

5V power test:

Pin 3 - 4.55V on IC3 assuming Pin 3 is 3pins in from the left side when oriented with the power supply plugged into the upper left. It would be good to add a picture of exactly where pin 3 is in the chip.

Bias Voltage

4.71V at resistor end closest to Q3

Kevin

[kevinsworld]

Just quick follow-on - I got the mis-oriented capacitors out with the help of a solder sucker and a bit of brute force but I pretty much destroyed them so I'll look to order a few more as replacements just to be safe.

[kevinsworld]

Does anyone from Adafruit know if these 20pF capacitors are 50v or 100v. Better yet does somebody have the exact part number from an external source?

[phild13]

I doubt you hurt anything by installing wrong.
Use 10PF 50V RADIAL as replacements for C8 and C9. The clock will keep better time. Here are the ones I have used in several clocks with the number.
Digikey# 445-4759-ND
Will Cost you about 30 cents each plus postage from digikey.com

[adafruit_support_bill]

What we ship with the kit are generic 20pF 50V parts - similar to this: http://www.mouser.com/catalog/specsheets/XC-600144.pdf

PhilD13 is quite familiar with these clocks and I'm sure that the parts he suggested work well also.

[phild13]

If anyone wants to read more about the capacitors, a number of us have found that the clocks keep better time if the value of C8, C9 is reduced to around 10pf. Here are a couple discussions about this that cover pretty well the capacitance of C8,C9 and the effect of various values for each.
viewtopic.php?f=41&t=49274&hilit=10pf
viewtopic.php?f=41&t=53793&hilit=10pf

[kevinsworld]

Excellent... thanks guys! Great to see active people helping out on these projects. I'll order those up and see where stand after replacement. It did not sound like it was going to fix my issue.

[kevinsworld]

Following up. Got the 10pF capacitors and re-installed those, correctly this time! The clock came up now with a time mode, which relates to what was stated in the FAQ. There were still missing segments in the digits so I went for the Q3 jumper and Voila! = all the digit segments worked. So my conclusion is I have a blown P-channel MOSFET (Q3). I thought I was pretty careful with this during assembly with an anti-static pad but it appears to be bad. A couple of photos to show the jumper and the working clock.

Can I email support to arrange getting another one?

Thanks,
Kevin

[kevinsworld]

Following up. Got the 10pF capacitors and re-installed those. The clock came up now with a time mode, which relates to what was stated in the FAQ. There were still missing segments in the digits so I went for the Q3 jumper and Voila! = all the digit segments worked. So my conclusion is I have a blown P-channel MOSFET (Q3). I thought I was pretty careful with this during assembly with an anti-static pad but it appears to be bad. A couple of photos to show the jumper and the working clock.

Can I email support to arrange getting another one?

Thanks,
Kevin

[phild13]

Glad to see you have it mostly working. While Adafruit will quite likely respond to your request there are other options for Q3 that you may also want to consider.

Here is an excellent post about Q3 where we discuss replacing Q3 with other options that are available.
viewtopic.php?f=41&t=51283 Russell did an excellent job explaining things.

The short version of the discussion is to replace the stock ZVP3306A (Q3) with a ZVP2110A FET or a PN2907A transistor. The ZVP2110A FET does not need a base resistor and is a direct replacement for the supplied ZVP3306A FET The PN2907A transistor requires adding either a 1k or 470 ohm base resistor (both work well and any value in between those two values will also work well) soldered to the middle leg of the transistor. This post describes how to solder the resistor to the transistor so it looks good.. http://forums.adafruit.com/viewtopic.php?f=41&t=43908.

I have used both ways of replacing the stock Q3 and both ways work equally well. Advantage of the transistor is it is not static sensitive like a FET is so the transistor is much harder to damage.

[kevinsworld]

Wow.. it appears you and several others have been deep into this thing for a long time as it was good reading with your links. Thanks a bunch for your reply and sharing of knowledge. It sounds like the 2907 is the way to go based on removing the issues related to static while solving the core issue. It looks like my local Radio Shack has the 2907... Is this the one that would work, if all 2907's are similar?

http://www.radioshack.com/pnp-bipolar-s ... Kbt5ca4l0s

I ask about this since Digikey shipping was a a bit much and a big giant box for my last two capacitors. I'm glad they were safely shipped. but a 10x10x2 box seems overkill.

If that's the one from Radio Shack I can solder up that configuration with the 1/8 watt 1K resistor from what I have read.

Thanks,
Kevin

[phild13]

Yes you can use the Radio Shack one and whatever resistor they have in stock that is within the 470 - 1K range.

Interesting about DigiKey. Are you selecting the postal service or another method when selecting a shipping method? Usually costs me a 1.50 or so for DigiKey to mail the electronic component parts I order for various projects and they usually come in a bubble mailer.

[adafruit_support_bill]

Kevin, if you contact [email protected] with a link to this thread we can send you a replacement. But many have had good luck with the other alternatives suggested also.

[kevinsworld]

Thanks adafruit Support (or can I call you Bill?).

I went the route of going to Radio Shack and got the 2907 and the 1/8W 1K resistor per the guidance of Phil and the greta links he provided and all is up and running great so I can conclude this thread I think. Good to know Radio Shack still has a few parts left to sell. Rumor seems to be they won't survive past this next year.

Phil - Once again thanks for your help and great participation here on the forums. I happened to have the Digi-Key shipping rates window open and the cheapest was...

U.S. Postal Service First Class Mail* (Ships next business day) $3.22

It just seemed overkill for .30 capacitors but I won't go broke ordering them in the end. :-)

PS - Adafruit - love the captcha resistor check for anti-Spam.... BRILLIANT!
Kevin