Original stereo in audi 1991 90

I have the original book it says anytime the battery is disconnected it will do the lock up and read SAF on the display when this happens you cant use it again untill you unlock it... to unlock it turn the radio on the word safe will be displayed first press the am/fm button and then press the scan button and hold them down simultaneously until "1000" appears in the frequuency display release the buttons DO NOT UNDER ANY CIRCUMSTANCE CONTINUE HOLDINT THE BUTTONS DOWN OR PRESS THEM ONCE AGAIN THIS WILL CAUSE THE RADIO TO TAKE THE NUMBER "1000" AS THE CODE NUMBER. using the first four radio station buttons enter the code number found on your radio card (the codes you have) use button 1 to set the first digit of the code button 2 to set the second digit etc. the first digit of a four digit code must be "1" if your code number has three digits the first digit on the display must be set blank. Once the code is shown on the display press and hold the am/fm button and scan button simultaneously until the work safe appears in the frequency display release the buttons a radio station frequency will automatically be displayed ... MAKE SURE YOU PUT IN THE RIGHT NUMBER OR YOU WILL LOCK UP THE RADIO AGAIN AFTER 2 TRYS AND WILL HAVE TO WAIT AN HOUR BEFORE YOU CAN RETRY IT. IF YOU LOOSE THE CARD WITH THE NUMBER SEE YOUR AUDI DEALER