Charles, which of the two printers do you have? The weak point on 804 is the heating unit, no idea where to get spares for that. The weak point for 605 is it's power supply, probably dryed capacitors. Additionally 605 has a countdown module, which you have to replace with the drum kit. Sometimes I have seen 1305 compatible drum kits on ebay without that module. New drum kit with old module won't print, and nothing found on how to reset that modue. You first should test, both printers would start with empty toner. At least for 804 you also could buy a cheap plastic bottle of Xerox "universal toner" which can be used to refill 804's toner box, Xerox also offers "developer", that is fine iron pulver which has to be added to the toner from time to time (Atari sold "initial toner" for that purpose, what is a mixture of toner and iron powder). But all of that does not make sense if the drum is too weak, you won't see well what has been printed.
Power without the Price. It's not a bug. It's a feature. _/|\_ATARI
1040STFM in PC-Tower (PAK68/2, OvrScn, 4 MB, 1GB SCSI, CD-ROM...) * 2x Falcon 030 32GB/14MB+ScrnBlstrIII * 2x TT030 73GB/20MB+Nova * 520/1040STFM * 520/1040STE * 260/520ST/+ * some Mega ST * 2x Mega STE 500MB/4MB+M.CoCo * Stacy * STBook * SLM605 * SLM804 * SLM605 * SMM804 * SH 204/205 * Megafile 30/44/60 * SF314 * SF354 * 5x Pofo * PC3