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VX 520 Troubleshooting 1. POS/Internet Help Desk: 1-800-541-5555. VX 520 Troubleshooting POS. March 2012. This section addresses problems that may arise while using the VX 520 Point of Service (POS) device. In. all cases, if the prescribed procedures do not correct the problem, call the POS/Internet Help Desk at. 1-800-541-5555 for assistance.