Preset buttons do not activate security code?

I have a Phillips SC201 cassette/radio that is currently locked out due to a battery change.
I have obtained the missing security code from a reputable supplier.
Upon following the instructions in the Vauxhall manual by switching on the ignition, holding in the AS button and turning the radio on I get a 6 ---- in the display.
I assume 4 attemps have previously tried and 6 more attempts are left.
My problem is there is no audible beep as described and the pre set buttons are having no effect.

Steve
September 2008