Different lot number part numbers reference the same part: CQ890-67023 CQ890-60251 CQ890-67097
I've had service calls on several T520 with similar error codes. The last one was BA7E70E6. The 'B' codes harkens back to the day when I routinely saw this type of error on the old 1050c\ 1055cm models. I used to tell customers you have the 'error code of death'. In more technical terms, the Main PCA Board has a defective chip or routine call somewhere on it and needs to be replaced. Replacing the (CQ890-67023 CQ890-60251 CQ890-67097) has resolved the error for me.