Well, I know how you feel - I also own a LaserWriter 4/600PS. Some days I think the thing just has a grudge against me...
I have often considered getting the memory upgrade for the printer (it comes stock with 2MB, upgradeable with an Apple specific 4MB card to 6MB), but I recently bought a new network printer for all my machines and I think I'm going to sell the 4/600PS. I never print Chinese text, so I don't know if the printer just doesn’t like the language (!), but I do get postscript errors all the time when trying to print PDF documents. Annoying.
I bought a second hand LaserWriter Pro 810 printer to replace all my other LaserWriter’s (the 4/600 and a LaserWriter Select). I got the thing for a great price and it works very well with all my hardware (Ethernet, Serial @ RS-232 port for PC's). While your probably not going to be able to find of these printers easily, I mention my solution because it has worked very well for me - and the features are pretty standard on lots of other laser printers to date, including a few from Apple.
The LaserWriter Pro 810 and 630 are both come with Ethernet standard (some 810's don't include it, but very few I think). The Pro 630 is probably the cheapest if you can find one. Also, the LaserWriter 16/600PS and 12/640PS is a very nice printers that includes Ethernet. Shreve Systems, Macresq, and MacWorks (the latter usually being pretty expensive) all carry used Apple LaserWriter’s. Check and see if any of them have any of these printers for sale at good prices.
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Eliott Wolfe
Winnetka, Calif