It may be one of the very very first A1200s produced, these had a problem with the modulator. I had one of these very first ones and used it with an RGB monitor. When the modulator news broke and I checked mine, sure enough - terrible 8-O
These were the days of "put in your own HD and you void the warranty". I had and did, so I had to haggle to get the motherboard replaced rather under a third party warranty.