As Harrison said, with a multimeter you can check if the wires goes to the right places.
You can pick a multimeter in any "loja do chinês" (Portuguese) it should be no more then 8 euros...
You can also look for the RGB output on the A500 to see if all pins are there, not the first time someone has 1 or 2 pins broken...
Can you test any other device in the SCART of your TV? Like a VCR, camera? Just to check if the scart on TV is ok.