It is either going to be 11.2896 MHz or 16.9344 MHz. Philips-based units are the first, J. A. Pan, Inc. versions use the latter. There is an outside chance some units run at twice the normal frequency. My guess is it is Philips based. The logos on the chips should give you a clue.
Besides, you should be able to see the crystal, and see the frequency on it. There will be other crystals for the micro, so that may confuse some.
Pat