In Sonys of that vintage they has alot of problems wit the CRTs. Usually the green for some reason. The gun gets weak and then shorts sometimes.

The AKB keeps the greyscale right until the green gun is too weak to do so. Then it is overdriven. This happens sometimes without notice.

The codes are not all that good. IF the main power supply is blown and it sees no voltage at the supply to the audio IC and thinks it is shorted. Like some cars, you read the codes ad they do not tell the whole story. You have to look over all the codes it actually has. In the US they standardised it, but not on TVs. But before that you had to interpret them by the model. And ironically if you got a code (even today) that says too lean alot of people think fuel filter or dirty injectors, but it really needs an O2 (lambda) sensor and is actually running too rich.

You actually could have a bad audio IC, you said it made a noise. But with the green on the screen with the (retrace) lines I suspect the CRT very greatly. The audio IC has nothing to do with the color.

If you really like CRT TVs, find a Toshiba somewhere. If the CRT is good after all these years it will probably be good for quite some time. Actually if you find a Sony from the 1980s that still looks good it might last a while.