Ice Tube boost converter only supplying 9.5V

[crazybutable]

Got to the part where I test the boost converter and I'm only measuring approximately 9.5V at the output. Input transformer is the one with the kit, I measured it's output at 10V.

I saw the previous thread, with someone with a similar problem, and he had a bad solder joint on the boost chip. I double checked my solder joint on the boost pin and it looks good. Then I double checked the rest of them.

Here's a top and bottom view:

top view

IMG_2320.JPG (951.42 KiB) Viewed 2403 times

bottom view

IMG_2321.jpg (656.82 KiB) Viewed 2403 times

It beeps when I plug it in. When I attached my USB oscilloscope to the boost pin, this is what I got:

Oscilloscope screenshot

oscope.png (111.98 KiB) Viewed 2403 times

Am I reading that wrong or is it saying it's getting a 20V peak to peak signal? If so I bet those clipped tops are from the scope's input protection circuits (it says 20V ptp max on the parallax USB scope itself). At this point I'm over my head.

I've plugged it in a few times now and it beeped every time, although I haven't done anything with it since I took this scope screenshot.

[adafruit]

clock seems to be good, are you sure you're measuring right? reading 10V at the input is a little high, maybe replace the meter battery

[crazybutable]

That's a good idea, my meter has been acting funny lately. But even after the new battery I'm still only measuring 8.8 volts on the output of the boost converter. Measured from the ground tab of the regulator and the tail end of D3.

[adafruit]

use your scope to look at the voltage on the 10K resistor R5

[crazybutable]

That oscilloscope image in my first post. I was measuring off the boost pin (pin 12) for that image, but when I measure off the 10K resistor, I get the same thing.

It's not a constant voltage, it's that goofy square wave.

[crazybutable]

It looked bizzare but it was repeatable. I tried the second channel on my scope and got the same thing. Then suddenly the display glitched, and I got something else entirely.

It's a series of 5v pulses at 31khz. I'm guessing the USB scope -> computer connection had a gremlin because that seems more likely.

[adafruit]

your ground isnt a good ground, get a good ground connection, post up the image from the 10k resistor

[crazybutable]

Looks like this:

oscope2.png (110.96 KiB) Viewed 2365 times

[adafruit]

the microcontroller is OK, so we suggest resoldering, checking parts around the boost that you did in the last step, is the inductor, FET, diode all soldered in right?

[crazybutable]

I've resoldered everything from the capacitor over and still no worky.

One thing that's a bit weird: I'm reading literally no forward voltage drop on diode D3. Both sides of the diode read 8.8v.

[stinkbutt]

D3's a Schottky. You'd expect the forward drop to be very very small, ~0.15 - 0.45v; You might be missing it on your meter.

[adafruit]

it sounds like your inductor is bad, try removing it and measuring the resistance or inductance if you have a meter

[crazybutable]

I removed the inductor from the circuit and it measures 0.01 ohms. I do not have an inductance meter.

[adafruit]

check the 60V zener, is the part number right?

[crazybutable]

Yep, it's a 1N5264B.

Also, since I had the inductor out anyway, I checked the pads of the inductor to make sure they had a good connection to each adjoining part of the circuit and they did.