ARM Technical Support Knowledge Articles

Versatile Baseboard USB Debug/Programming port does not work

Applies to: Versatile Baseboards

Answer

[New 4 Sep 2007]

Symptoms:

This problem has been seen on a few Versatile EB, AB926EJ-S and PB926EJ-S baseboards. When the 'USB Debug' port is first connected to a host PC after power up, the green 'USB Debug ON' LED will not light and progcards cannot find the USB hardware. (Note that on the AB926EJ-S board, the silk screen labels for 'USB Debug Busy' and 'USB Debug ON' are swapped).

Cause:

The USB chip on the development board does not start up correctly. The USB chipset is powered by a TPS78833 low drop-out voltage regulator, which has a selectable start-up time to limit in-rush current due to capacitive loads on USB. The value of the capacitor that sets the start-up time is such that the USB chip does not start up properly on some boards.

Workaround:

Plugging the USB cable in/out of the board or host PC will usually reset the USB chip and allow a connection to be made. If this does not work or is not a satisfactory solution, a permanent solution can be effected by changing a single surface-mount capacitor. This is detailed in the following paragraph:

Permanent Solution:

To permanently fix the USB power up issue, replace the 100nF '0603' capacitor (between TPS78833 pin 4 and GND) with a 1nF '0603' capacitor (AVX part number AVX 06035C102KAT).

 Board Type

 Component References

Location

 EB

U47, C143

Top side of board, ~30mm NE* of silver XC2V6000 FPGA

 AB926EJ-S

U51, C199

Bottom side of board, next to SW corner of black XC3256 FPGA

 PB926EJ-S

U67, C234

Top side of board, ~8mm E of black XC3256 FPGA

* Compass coordinates in the table are with reference to the writing on the FPGA package.

How do I arrange for this modification to be applied?

The quickest and recommended solution would be to have the modification performed locally by someone who has the necessary soldering skills and equipment - these capacitors are about 2mm long and 1mm wide. This modification should only be performed by someone experienced in working with small surface mount PCB technology. A very fine soldering iron tip and minimal contact time must be used to avoid damaging the PCB pads.

If it is not possible for the modification to be performed locally, the baseboard can be sent back to ARM in the UK to have the work done, free of charge for boards which a) are covered by a current support and maintenance contract, and b) exhibit the problem. This workaround is not required for baseboards that are not used with the USB Debug Port or do not demonstrate the symptoms listed above. Boards that are more than 1 year old and are not covered by an extended support and maintenance contract will be modified by ARM for a nominal fee.

To have ARM perform the modification, please use the existing returns process, which is described here. Please familiarize yourself with the procedure and submit an online fault report by following this link.

How much time is needed for this modification?

If the modification can be performed on-site, by a competent person, the modification should take substantially less than 1 hour. If the board is shipped to ARM (UK) to have the modification done, this may take several weeks including transit time.

Will I invalidate the warranty?

If the modification is performed by the end user or his representative and the board subsequently fails and must be sent to ARM for repair, we will honor any remaining warranty - provided the fault is not related to any user modification.

Article last edited on: 2009-01-20 11:08:01

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