Ice Tube boost stopped working?

[Agent24]

What would cause an otherwise sane boost converter in an Ice Tube clock to stop boosting?

In the original test I got the single beep and proper 60 volts output, but after adding the rest of the parts the tube did not light (although it still beeps)

Upon powering off, the tube flashes once, dimly and briefly with all segments lit (residual current from inductor?) - but at least I assume this means the tube is OK.

Now the boost output is the same as the input (10 Volts), I guess the FET is not switching?


I'm getting 1.5v out of the BOOST pin from the ATmega168 (no oscilloscope so can't actually test properly) but the boost converter seems to be doing nothing.

Would I be correct in thinking that the FET (IRFD110) has somehow broken?

[adafruit]

could be, or the micro chip is broken

[Agent24]

Yeah I also thought that could be an issue, a few people on the forum seemed to have the same problem, with the result that the Atmega168 was stuffed - although it seems odd if there's an output of some kind from the boost pin (though who knows what a broken one might do?)

I've ordered a new one of each so will try both out, guess we'll see what happens

[adafruit]

without a scope or frequency meter it will be hard to tell

[Agent24]

Tried a new ATmega168, same problem, although strangely it didn't beep straight away after turning on like the old one does.

The new one however is the 20PU version, perhaps that's why?

I guess I will need to get my hands on a frequency meter and see what's coming out of the boost pin...

[adafruit_support_bill]

Check to see that the you have a good ground on the jfet http://forums.adafruit.com/viewtopic.php?f=41&t=19130&p=99558#p99558

[Agent24]

This is getting weird. The clock has sat to the side of my bench for a while now, so I figured I better start on it again.

Recently I purchased second hand, a basic oscilloscope, and so I measured from Pin 12 of the ATMega168. I saw a square wave.

Since said oscilloscope has unmarked controls (I said it was basic! ) I also borrowed a frequency meter, and measured the boost output at 32.4Khz (a bit high perhaps, seems close enough? - but the meter is old, and calibration might be off too)

I guess it would appear the boost signal is working OK, though.


I then pulled the 22uF capacitor and it seemed to test OK at 17.5uF on my meter.
I also pulled the inductor, and measured resistance at 4.4 ohms (don't have inductance meter) but I guess it's OK too.
I put the capacitor and inductor back in, and my next suspect was the IRFD110 FET.
I swapped this out with a new one, and tried again.

I saw '50' briefly flash on my meter before it came down to 11.5v and stayed there.

This is with no MAX6921 or Tube plugged in, so they can't be the problem now. Checked MOSFET ground as suggested before, all OK. Perhaps the Zener has gone funky? Can't see any issues with my soldering, and the thing did work fine the first time I tried it. Gah.....

[adafruit_support_bill]

Since you have a scope, check the pins on the tube. You should be seeing activity on the digit pins (VFD_1 - VFD_9) as well as the segment pins (VFD_A - VFD_H).
Make sure you have ~4.8v on the bias pin too.

[Agent24]

Since you have a scope, check the pins on the tube. You should be seeing activity on the digit pins (VFD_1 - VFD_9) as well as the segment pins (VFD_A - VFD_H).
Make sure you have ~4.8v on the bias pin too.

Thanks for the suggestion, but I am not sure how that can be used diagnose the boost converter?

[adafruit_support_bill]

Sorry, I should have read from the beginning.
Using your scope, what do you see between the inductor and the diode?

[Agent24]

At the anode of D3 I get another square wave. It appears to match the frequency of the signal from boost\pin 12 as I did not need to adjust the sweep for it to be viewable (10-100kHz range) The vertical gain had to be reduced to see it as the voltage was higher: The voltage measured at that point with my DMM is 8.5v

Next to the capacitors, the voltage on the cathode of D3 is 11.5v, and at the same frequency range as the other two voltages the waveform appears simply as a line.

However if I reduce the sweep frequency, down to the 10-100Hz range I see a waveform that seems indicative of the smoothing action of the capacitors.

So it appears the circuit is working to some degree, but the voltage is too low for some reason. Of course the voltage does jump higher than 11.5v at switch on and switch off.


I've attached photos of the waveforms.
1) Output from Boost\pin 12
2) Anode of D3 (same settings as (1) but with increased vertical gain attenuation)
4) Cathode of D3

[adafruit_support_bill]

I suspect the inductor. It looks like the JFET is just switching ~9v. You should be seeing a healthy spike from the inductor as the field collapses, not a square wave.

To get a better idea of the vertical scale, you should calibrate your scope against a known voltage source. Then label the controls for future reference.
Since you have a frequency counter, you can do the same with the horizontal scale too.

[Agent24]

That's the last part I would have expected, but what you said obviously makes sense. I wonder how the heck it could have failed though?

Anyway, we'll soon see what happens, I've ordered a new one, and some spare diodes also just in case.

And thanks for the tip about labeling the oscilloscope controls, sounds like a good idea

[adafruit_support_bill]

I wonder how the heck it could have failed though?

Good question. I think I've only ever seen one bad inductor (a poorly-trimmed lead connection had shorted into the coil). I would be more inclined to believe that it is a bad connection or short on the board.

I also pulled the inductor, and measured resistance at 4.4 ohms

I checked your measurement against one here and get about the same resistance (4.3ohms).

However, you said you're self-sourcing and DIYing your own kit - so at this point we're going to ask you keep the forum clear for our kit customers and allow us to support them!

Thank you!
Adafruit

[Agent24]

I am sorry for any misunderstanding about the clock. I thought you did know I was doing it DIY, but were being nice and helping anyway. In any case, I am very grateful of your help.

In the future I will be more clear if a build is DIY so as not to take up your support time unnecessarily.

I will keep this thread updated on any changes in case it helps someone else. Hopefully the problem will be resolved soon!

Thanks again