[SOLVED] Crazyradio PA death (D1)

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ccpost
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[SOLVED] Crazyradio PA death (D1)

Post by ccpost » Tue Apr 25, 2017 2:00 am

Hi all,

I've solved my own problem for the time being, but I wanted to post here in case anyone else found themselves in similar trouble, and with a couple of follow-up questions.

First off, thanks so much for publishing the schematics! This would have been *much* harder to diagnose without them. Open source hardware for the win.

I just had a Crazyradio PA (Rev C) die out of the blue. The red LED lights dimly (no green), and on macOS I see repeated kernel messages like

Code: Select all

default	16:20:26.844627 -0700	kernel	536414.581065 AppleUSB20HubPort@14144300: AppleUSBHostPort::disconnect: persistent enumeration failures
when connected. Connecting through a USB current meter, it draws only around 2mA when connected (as opposed to the 17mA a working one draws). Probing with a multimeter between pins 3 (3V3) and 9 (GND) on the header yields around 2.5V. Measuring pin 1 (IN) on the 3.3V regulator also yields around 2.5V. D1 is the culprit for the voltage drop between IN and USB VCC. Testing D1 with a multimeter yields around 1.8V forward drop (open circuit reverse) on the diode tester, compared to around 0.2V (what you'd expect for a Schottky diode) for D2.

To fix, I removed D1 and D2, then replaced D2 on D1's pad. (I figured I'm unlikely to to supply unregulated voltage from the header.) Good as new!

Now for a couple follow-up questions:

1) Any idea what the failure mode might have been?
(Static, heat, prolonged operation, etc...) If there's some way I can be more careful I'd like to do so. :-)

2) Are the Rev C schematics posted anywhere?
All I could find was Rev D (https://wiki.bitcraze.io/_media/project ... matics.pdf) and Rev B (https://wiki.bitcraze.io/_media/project ... _rev.b.pdf). For this Rev D was enough to hint me at the problem, but it'd be nice to have C as well.

3) Is R3 related at all?
I noticed in Rev D there's a series resistor in-line with the input that's not on my board. Is this a design change that was meant to address something related?

Thanks again for all your work on this product!
Last edited by ccpost on Tue Apr 25, 2017 6:13 pm, edited 1 time in total.



ccpost
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Re: Crazyradio PA death (D1)

Post by ccpost » Tue Apr 25, 2017 2:10 am

Also I guess:

4) Do you have the manufacturer + part number or specs for D1?
I imagine most anything slightly over-specced will do, but I'd like to just get some next time I'm on Digi-Key.

tobias
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Re: Crazyradio PA death (D1)

Post by tobias » Tue Apr 25, 2017 6:43 am

Great and detailed explanation and nice troubleshooting, thanks!

I'll do my best to answer you question.
1) One possible cause might be a short circuit of VCC which could blow the schottky as it is only specified for 300mA.
2) There is no functional change from Rev.B and Rev.C schematics so that is why it never has been updated. To avoid confusion I will add a ticket to update it anyway.
3) R3 (part of low pass filter) is not used in the PA version as that consumes to much power due to the power amplifier and thus not viable to have the resistor.
4) Nearly and schottky in SOD-323 package will do and we used BAT54JFILM

ccpost
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Re: Crazyradio PA death (D1)

Post by ccpost » Tue Apr 25, 2017 6:12 pm

Perfect, that answers all my questions. Thanks!

I'll look into printing something like https://www.youmagine.com/designs/crazyradio-housing or http://www.thingiverse.com/thing:130857 to protect against possible shorts from handling.

H0stname
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Joined: Fri Feb 17, 2017 5:44 am

Re: [SOLVED] Crazyradio PA death (D1)

Post by H0stname » Wed May 03, 2017 10:25 pm

I recommend this one:
http://www.thingiverse.com/thing:84295

I printed/verified it actually works, and it grasps the board the right way for when you're yanking it out of your USB ports without pulling the sensitive SMA connector.

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