"50 Service" on an HP printer means that the fuser is not working (not reaching an acceptably high temperature within an acceptable time period, or, rarely, it's stuck on and overheating). In these particular models, the fuser is a heated roller system, there is a pressure roller (silicone rubber with a special "oil" on it to prevent sticking) and a heating roller, a hollow aluminum tube (also with a special silicon coating) with a heating element inside it. The heating element is a very high power cylindrical quartz lamp running the length of the center of the aluminum tube. The most likely cause of your problem is that the lamp has burned out, although there are other possibilities (rare, however). These can be replaced, but it may not be economical to do so. Also, examine the roller carefully, if any of the coating on the hollow aluminum tube has worn off, the tube should be replaced also (at some point, bare aluminum will literally leave brown scorch marks on the paper). These parts are available, but expect to pay $30 to $50 each for a new lamp and tube. The job is not that difficult if you know what you are doing, but substantially more difficult if you don't (big surprise, right?). You may be able to buy an entire working fuser assembly for less, but the lamp may have thousands of hours on it and the roller may be well worn. If you plan to keep the printers, a "true fix" with new parts really is the best way to go. Be careful working in this area, the lamp is AC line operated, and the roller is heated to nearly 400 degrees F. There are both shock and burn hazards. I have an actual factory service manual for the Laserjet II, I may scan it and make it into a PDF for the classic computer documentation effort. However, unlike Imsai, Altair, etc., HP is very much still in business and may take legal action if their copyrighted manuals are put on the web or otherwise distributed. I have found Laserjet IV service manuals on the web, and I have them downloaded. Just a note on economic viability, you can buy entire working HP 4 printers -- HP 4 Plus, the 12ppm version -- for well under $50, so putting in a $60 repair on a vastly inferior Laserjet II is of questionable economic viability.