The "50 Service" Error on a Laserjet III

This is apparently a pretty common problem on these printers, and it means either the fuser or the AC power supply is bad. On mine, it turned out to be the power supply, and this is how to take care of it:

A prety good way to visually check is to open the rear cover of the printer and watch the light in the corner as the printer is turned on. On mine, with a bad power supply but a good fuser, the light came on for a few seconds and then shut off with a "click". After the new power supply was in, it just faded out silently. However, since you have to take the fuser out anyway, you might as well check it. If there is no light at all, it's probably a burned-out fuser. I don't know what they cost, but a refurbished power supply cost me $25.


1. Test the fuser. (You'll need a multimeter, a Phillips screwdriver, and probably a magnet.)

Remove the toner cartridge if you need some working room, and then remove the fuser (the thing with green felt on it that says "Hot!". Regard this warning, because it may be true). There are four screws that hold it, one at each corner. Two are fairly accessible, and two are semi-accessible. I found that my magnetized screw-picker-upper tool was indispensable for getting these last two screws in and out. Also, if you end up dropping a screw into the works, you'll have to fish it back out again.

Once the screws are out, take the fuser and lift it straight up. There is a connector on the left side that you need to be careful not to bend. The plug to the AC power supply is on the right side. Test this first. There should be very little resistance across these contacts (mine was around 3-4 ohms). If it's open, the fuser is bad.

If that checks out ok, remove the small black screw that holds the plastic cover on the left side of the fuser, and test the two contacts detailed in the picture below. There should be about 1meg ohms resistance at room temperature--if it's wildly off, the thermistor is bad, and as far as I know you'll have to get a new board, if one doesn't come with a new fuser.


If the fuser checks out OK, then most likely it's the AC power supply. This is what those two white contacts plug into, and it contains the main power switch and plug.


2. Replace the power supply.(As far as I know, there's no way to easily test it.)


Make sure the printer is UNPLUGGED! If it hasn't been all this time, you deserve the shocking you'll probably get. Also remove the paper tray.

Find all the screws that hold the printer case in place (two in brackets on the inside left back, two along the front top where the cover closes, one directly over and another on the inside back panel above the power supply, and one by the power cord plug.) Once all these are out (and try to remember which ones came from where), you should be able to jockey the case over the power supply and then tilt it up toward the front of the printer. Don't worry about the cables to the buttons and display, they're long enough to stay in place.Let the case sit on its face after you've tilted it far enough to get to the power supply.

Remove the two screws the hold the ozone filter and plenum to the fan. Then remove the screws that hold the power supply--I think there are four, but they're easy to find--they're all screwed to the floor of the printer, and one is in the back by the plug. Then lift the power supply straight up to avoid bending the plugs on the bottom. Remove the three screws that hold the fan and plenum in place, unplug the fan, and there is your power supply.

Get a new one, and, like the Chilton manuals say, installation is the reverse of removal. When you get to putting the case back on, make sure the pegs on the inside front bottom left and right go into the slots on the sides of the printer properly--the bottom of the case should be aligned with the bottom of the printer, the cover open button should be flush, and the two brass-lined bolt-holes on the top front should line up perfectly (as should all the rest). It takes a little effort to get the case back on - there's a way to remove the side panel, but it turns out that you can squeeze the back panel over the plug and get it back on without too much trouble. Just make sure the case is flush against the bottom of the printer. Then replace the fuser and toner, shut the lid, put the paper cartridge back in, and turn it on. You'll notice, if you open the rear cover while the printer is running its self test, that the light no longer cuts out with a "click", but fades quietly away.

If you hear a strange chattering when the printer powers up, there's a little black plastic piece directly in front of the fuser, on the side by the power supply. The little tab should be under the plastic, not over it. It's easy to dislodge when removing the fuser. Just pop it back in.

Links: (This is where I get power supplies.)


Note: A laserjet II uses the same internal SX engine as the Laserjet III. Therefore, these instructions may be used without modification, except for the removal of the extra screws that hold the case.

Don't break your printer doing this, because I am not liable. These instructions are based on my own experience, and are definitely not guaranteed to fix your problems. But I hope they help.


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