LaserWriter 8500 Scanner motor

[beachycove]

I have a LW8500 here that of late has been giving me persistent "ROS motor" errors. There is a documented fix "out there," but which in my case hasn't fixed anything (involving placing a shim underneath the cartridge sensor), so I am going to dig into the guts of the thing and see if I can document another fix for it if I can.

So far I have established that in all B&W lasers, the scanner motor does not spin up until a print job is sent. This would explain why the printer starts up normally. The machine's normal POST tests (normal startup diagnostics done on booting) show that everything is so far good. It does not report any error until a print job is sent (an error which is now reported most but not all of the time).

I just did an ePOST startup test (i.e., an extended POST or diagnostic test, which is done by shorting pins 1+2 and 3+5 of the localtalk port). The machine reported an optical scanner error.

I have developed a theory:

It is hard to find information about the LW8500, as it was a rare an somewhat eccentric beast of a thing, but apparently certain much more common HP printers from the same time as the LW8500 had a similar affliction, giving a scanner motor error — the fix being that the scanner motor (which spins at something like 15000-20000 rpms) needs bearing lubrication. My hunch is that Fuji-Xerox most likely used the same motor. How many manufacturers of little high rpm, mirror-spinning motors for laser printers could there have been around 1997? Alternatively, the Fuji-Xerox engine exhibits the same symptoms, even if the motor is different.

Good hunch? And has anyone attempted this fix on an older laser printer?

 

[beachycove]

Took it apart this evening. That part of the operation takes about an hour, as the whole top and side of the printer basically comes off to get at the scanner assembly. The encouraging thing, however, is that when I got to my goal, the description of the Laserjet motors that I mentioned in the previous post turned out to fit the LW8500 like a glove: e.g., http://www.fixyourownprinter.com/forums/laser/42093 .

I can feel a little roughness in turning the mechanism with my fingers, which would presumably be A BAD THING at very high rpms, more or less like an ageing water pump in a car that feels just a little rough to the hand nevertheless makes its presence known by grinding loudly when you drive down the road.

In the scanner motor, there is a ball bearing assembly around the driveshaft that I will lubricate. The good thing is that nothing is yet stiff, so no real damage has yet been done — the printer has, after all, been lightly used. But I will need to get some better machine oil than I presently have to use on it, before reassembly and testing. Will post the results in the next day or two.

It will be interesting to see not only if it works, but whether the scanner motor whines less on reassembly.

Fingers crossed!

 

[beachycove]

I went at this again in the morning — me being anxious to see whether or not I would succeed — and we have a positive result. The machine is behaving normally.

Since this is not found anywhere on the web, I will spell it out here:

The "ROS motor error" that is characteristic of the LaserWriter 8500 can be caused by a "Raster Optical Scanner" motor that is in need of lubrication. Without it, the motor does not get up to speed in the first seconds after a print job begins, printing is aborted, and an error is reported. Or, to put it another way, the symptoms are that you send a print job, you can hear the scanner motor's high pitched whine as it tries to spin up, and then it stops/ spins down without doing anything, followed by the top two lights on the panel flashing amber. A restart of the printer is then required. Sometimes the printer will print, but it is erratic.

EPOST testing in my case, as I explained last night, showed that the scanner was faulty. The service manual's fix for this is to replace the whole scanner assembly, which these days is pointless as there are almost no parts available, and any parts available would likely have the same problems anyway after all those years. The lifespan of lubricating oil is finite.

The fix in my case was first to check the cartridge sensor assembly, which is a known solution in some cases, and not that hard to do. Mine was fine. (I found, by the way, that Apple supplied the LW8500 with two versions of this sensor; the revised version came with shimming ridges underneath the assembly, intended to ensure contact and solve the problem — and mine had these ridges.) So I decided to dig into the machine. This involved partial dis-assembly of the printer to extract the scanner assembly (a service manual is needed), removal of the scanner assembly cover (four screws and some tape), removal of the motor (three screws), removal of the (white in my case) plastic cap on the end of the motor bearing, inspection of the bearing, and a couple of small drops of light synthetic machine oil applied to the bearing (not too much or there is a danger of it betting flicked onto the lens etc.). These steps are not in the service manual, so that is why I am spelling it out. Reassemble in reverse order. The fix is probably 3-4 hrs work, depending on ability.

I should also add that after lubrication, the scanner motor is now scarcely audible, and that I was able to wash the machine's plastics (as the panels had to be more or less all removed from the machine for dis-assembly per the service manual). I also cleaned the scanner lens and mirrors with compressed air (don't touch!) before final reassembly, since it had to be opened up, and since it is not meant to be open to a world full of dust.

So my LW8500 is spic and span as well as working again.

 

[olePigeon]

I had hoped to get one of those at some point, but they're hard to find and/or expensive. They look awesome next to an 8600/9600 or Beige G3.

 

[beachycove]

Yes, I was the same and looked for ages for one that was affordable/ had a low page count. Mine has printed only a little over 14,000 pages — one toner cartridge. I think it may be because it developed the ROS motor error in its past life.

The downside is that a) the machine is enormous and B) has a couple of characteristic defects (honestly not that hard to fix, though). However, the biggest problem these days is c) finding affordable toner. I am currently sourcing enough parts to rebuild five or six cartridges myself (which will theoretically give me something like 90,000 pages), as I discover that this will take a good bit of the financial sting out of the business.

There's a supplier in Italy that is the best of the lot, in terms of both prices and supplies, but it won't ship to me (domestic shipping only). Another is in Poland, and they will ship, but they are not cheap. Strangely, I can find very few cartridge parts in North America for the thing: most links are dead, etc. I have just tracked down a couple of wiper blades and drums in Toronto, but such supplies as do exist are few and far between.

 

[beachycove]

These, I discovered at a local company in my own corner of the world, of all things, and they tell me that they are newly manufactured rather than remanufactured or remaindered old stock. I have ordered one, as the price is 1/3 of what some of the remaindered stock sells for, and is competitive with the price of remanufactured cartridges. They come with a standard two year guarantee, as well.

 

[beachycove]

And I was misinformed. Cartridge is discontinued, and my money has been refunded. Back to the parts search....