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Background: We are in the process of developing a sensing application. We are currently using an Evaluation board from a vendor for initial development work that has a MSP430 microcontroller.

The first version (000) of the board had 240 ABMM I3C Ceramic surface mount microprocessor crystal from Abracon on the board. This evaluation board with custom software works fine.

The second version (001) of the board has a 240 ABMM F4C crystal. The second board with the custom software doesn’t work at all. Although the crystal is from the same vendor the crystals appear to be slightly different.

Picture of Crystal from the working EVM board

Crystal I3C
Click on image for a larger version of the image.

Picture of Crystal from the defective EVM board

Crystal F4C
Click on image for a larger version of the image.

Below is the schematic for the crystal

Schematic

Question: What is the difference between the two crystals? (I3C vs F4C)

Note: I'm wondering if one of the components is not a genuine part and is a knockoff.

References:

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  • $\begingroup$ Can you post the schematic for the crystal and micro-controller? $\endgroup$
    – user1586
    Nov 16, 2015 at 23:13

2 Answers 2

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Are you sure those are really genuine Abracon crystals? The markings and packaging look Abracon-like, but the details don't match the datasheet you linked to. Abracon may use that case in different series, so possibly there is a different datasheet that actually applies.

Without the datasheet you don't know if it's a date code, tolerance indicator, tells you the required load capacitance, or something else. The "240" probably indicates 24 MHz, but that's just a guess, and is contrary to what the datasheet says. Send the picture to Abracon tech support. They can either tell you what the markings mean, or who the counterfeiter is.

As for the second not working, you've only said the whole thing doesn't work. There is a lot more to a micro running than the crystal. Check with a scope to see if the crystal is oscillating. Make sure to use the highest impedance probe setting, and probe the output of the micro (into the crystal). I have seen even 10x scope probes kill the oscillation if placed on the output of the crystal.

Even if the crystal is not oscillating, that doesn't mean the crystal is broken. Something else, like a bad solder joint, may be keeping the micro from turning on the crystal driver.

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  • 240 ABMM I3C is 2013/September date code
  • 240 ABMM F4C is 2014/June date code

Abracon ABMM date code

More details can be found at Beckwith Electronics/Abracon Corporation.

Also try re-flowing the solder around the crystal. Also based on the image it appears that the crystal is some distance away from the micro-controller. It is best to place the crystal and the capacitors as close to the micro-controller.

Also look like the load and shunt capacitance are don't match the crystal specification too.

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