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help with low voltage on USB pins 2,3
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help with low voltage on USB pins 2,3

by paultravers on Sat Dec 07, 2013 1:45 pm

Hi,

I have the following problem with a mintyboost v3 that I soldered today -

checking the usb pins, I get 5V from GND to 5V (which is a relief!), but only 0.15V from GND to D- or D+. The values from 5V to D- or D+ are both 0.23V.

If I measure from GND to either end of R2 or R4 I get 5V at one end and 0.15V at the other; if I measure GND to either end of R1 or R3 I get 0 at one end and 0.15V at the other. This at least is consistent with the schematic - but not why I only get 0.15V in the first place.

The solder side of the MB is as below:
DSC_8217.jpg
DSC_8217.jpg (67.95 KiB) Viewed 1539 times


Can anyone suggest which joints might be faulty to give me the symptoms I see? I have reworked some of the joints that looked a bit dodgy but get the same result.

All help gratefully received.

Paul

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Sat Dec 07, 2013 2:02 pm

Strange that both resistor dividers are giving you exactly the same wrong voltage. Do the resistor color codes match the ones in the parts list? Post a photo of the front of the board also.

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Re: help with low voltage on USB pins 2,3

by paultravers on Sat Dec 07, 2013 7:34 pm

I thought it was strange too, given the simplicity of the circuit - i didn't think I'd have an identical soldering error on two different parts of the circuit; maybe on something in common between them?

Here is the front view:

DSC_8218.jpg
DSC_8218.jpg (59.47 KiB) Viewed 1521 times


Its not the greatest view, given the short focal length of a macro lens, but you can see the resistor colours.

Is this clear enough?

Paul

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Sat Dec 07, 2013 8:22 pm

I can see R4 and R2 pretty clearly and they do look correct. I can't really see R1 and R3.

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Re: help with low voltage on USB pins 2,3

by paultravers on Sun Dec 08, 2013 11:36 am

Here are better views of the resistors .. First R1 and R2

DSC_8226.jpg
DSC_8226.jpg (33.3 KiB) Viewed 1501 times


then R3 and R4

DSC_8225.jpg
DSC_8225.jpg (37.16 KiB) Viewed 1501 times

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Sun Dec 08, 2013 12:02 pm

The components all look right. Reading back over your original post, the voltages don't add up:

I get 5V from GND to 5V (which is a relief!)

That is as is should be.
but only 0.15V from GND to D- or D+. The values from 5V to D- or D+ are both 0.23V.

That only adds up to 0.38v. It should add up to 5v.

One possibility that doesn't violate any laws of physics is that there is no connection to D-/D+ - although your solder doesn't look bad and it would be odd that they both float to the same value. Try these measurements once again. Also measure the resistance between GND & D-/D+ and also from 5v to D-/D+.

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Re: help with low voltage on USB pins 2,3

by paultravers on Mon Dec 09, 2013 2:32 pm

ok .. rechecked the voltages - with a new batty in the multimeter (just in case).

GND to either D1 or D2 is 0.16V; 5V to D1 or D2 is 0.24V.

The resistances measured are:
GND-5V : 67 KOhms
GND-D2 : 41 KOhms
GND-D1 : 39.1 KOhms

5V-D2 : 50.3 KOhms
5V-D1 : 50.3 KOhms

Does this shed any light?

Paul

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Mon Dec 09, 2013 3:35 pm

Hmmmmm. Your Mintyboost is in violation of several laws here. A bad R2 & R4 might explain some of it. But the fact that your GND->D1/D2 plus your D1/D2->5v measurements don't add up is puzzling.

If you de-solder one end of R2 and R4, do your measurements change?

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Re: help with low voltage on USB pins 2,3

by paultravers on Tue Dec 10, 2013 6:38 am

yes, if i desolder one end of R4, no voltage on D- pin and GND to D- is 49.8 KOhms. I notice that the resistance to the other pins is slow to settle down, and takes a few minutes to reach a stable value, while this GND-D2 measurement was almost immediate.

I will try to desolder R2 as well and let you know the results

Paul

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Re: help with low voltage on USB pins 2,3

by paultravers on Tue Dec 10, 2013 7:10 am

OK, desoldered R2 and R4, GND to D+ or D- is 49.8 KOhms in both cases. Stable readings. 5V to GND, D+ or D- is not stable but seems to be levelling somewhere around the 550K Ohms mark

Paul

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Tue Dec 10, 2013 7:32 am

I notice that the resistance to the other pins is slow to settle down, and takes a few minutes to reach a stable value

There are capacitors in the circuit, so when you try to measure resistance it is charging up the caps.

Now that you have R2 and R4 effectively out of the circuit. What is the resistance of these two resistors (should be as-marked - but clearly something is wacky in this circuit).

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Re: help with low voltage on USB pins 2,3

by paultravers on Tue Dec 10, 2013 8:05 am

They are 75K and 74.7K Ohms

Paul

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Re: help with low voltage on USB pins 2,3

by adafruit_support_bill on Tue Dec 10, 2013 8:30 am

They are 75K and 74.7K Ohms

As they should be. The engineer in me wants to understand this mystery. But I suspect this investigation may be holding up a holiday gift. If you contact support@adafruit.com with a link to this thread we can send you a replacement MintyBoost kit.

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Re: help with low voltage on USB pins 2,3

by paultravers on Tue Dec 10, 2013 8:34 am

The scientist in me would love to understand it too ... it's very frustrating ... but in the meantime I will contact support as you suggest. Thanks for your time in trying to debug this.

Paul

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Please be positive and constructive with your questions and comments.