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NeXT 400dpi laser printer restoration

Yup, definitely a problem with the fuser circuit. Doesn't get hot and this stays around 4.5-5 Volts:
1683839538014.png

GiGaBiTe said:
Going too high of a voltage can be a problem, because high voltage capacitors have a different internal plate layout that changes their characteristics.

From 35 to 50v generally isn't an issue, but to 63v is when the internal plate layout starts to change. This usually results in substantially different ESR.

If the circuit works, I'd monitor it for awhile to see if anything is getting excessively hot. If you start having weird phantom problems, remember that capacitor, as it may be the culprit.
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I'll try procuring the correct capacitor, as it plays a role in the protection circuit:
1683839618898.png

@Paolo B, do you mind measuring the heater lamp resistance if it's not too much of a hassle? I'm going to get it out after replacing the cap if there's still no heat from the lamp

 
News from the its-never-easy-department: I've changed the suspected cap with a correctly rated 22uf / 35V part and it didn't change anything.

Now i took apart the fixing unit and got the lamp out, Ushio VA3 1100W 240V, approx. 30.5cm in length including the holder. It measures 4 Ohms and doesn't look damaged.

next-printer-11.jpg

Is there any way to test it? Hook it up to a wall socket?

If the lamp is good, what could be the issue...
 
This fixing unit is endless frustration... I took it further apart and the drum is caked with gunk or toner... it can't clean it off with IPA and q-tips.

next-printer-12.jpg

I tried checking the sensors and the thermistor goes down in resistance (from 1.3 MOhm to few dozen KOhms), but the thermoswitch I can't get reaction out of it. It says "Elmwood 2450RC", and it's just open no matter if I torch it or not.

The datasheet and service manual suggests it should be closed:

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Guess I'll start with replacing TP1.

Furthermore, there's a gear that seized and has become cheesy / ground down on one side. It drives the rollers that pull out the paper

next-printer-13.jpg

Now where the heck am I going to get a replacement for this... I managed to somewhat unstick it but this also begs the question, what can I use to grease the gears again? I would like to avoid breaking more of them....
 

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An open thermal switch isn't an uncommon problem with laser printers from this era. Replacing it should fix the problem. The fuser is usually turned on and off with a triac controlled by the engine controller. If this is shorted, the fuser might have overheated, and caused the thermal switch to open.

The fuser roller will probably be easier to clean when it's hot. Unless it leaves marks on the page, it may not matter. It's teflon coated, and should clean itself when the printer is used. If not, a stronger solvent like acetone should work (test it on a small area at the edge first).

For lubrication, use something that can take high temperatures. Possibly grease intended for car brake calipers would work.
 
andy said:
An open thermal switch isn't an uncommon problem with laser printers from this era. Replacing it should fix the problem. The fuser is usually turned on and off with a triac controlled by the engine controller. If this is shorted, the fuser might have overheated, and caused the thermal switch to open.

The fuser roller will probably be easier to clean when it's hot. Unless it leaves marks on the page, it may not matter. It's teflon coated, and should clean itself when the printer is used. If not, a stronger solvent like acetone should work (test it on a small area at the edge first).

For lubrication, use something that can take high temperatures. Possibly grease intended for car brake calipers would work.
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Thanks, I found CRC silicone lube (the one with gears on the bottle), which is rated for up to 200 °C. I would have tried to bridge the switch to see if anything works but if there's a risk of overheating I won't... at least not before checking the triac. The switch is self resetting but it seems they like to break from time to time.

Paolo B said:
Here you may find the right replacement

Laserjet Ii | Partsmart | Toner Cartridge, Ink Cartridge, Laser Printer Parts, Fuser Assembly, and Plotter Parts | Offical Site

www.partsmart-corp.com www.partsmart-corp.com
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They don't have it on the page, but on eBay. I have to contact them to ask about international shipping as well. Any other parts worth ordering? They have the broken gear, but at that point I might replace all critical parts.

Paolo B said:
You will pardon me if I don’t touch the fixing unit in my printer, I see that you already verified that the fuse lamp is OK.
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Yes no problem. There's something that I would be curious about, namely the resistance at J-112? Mine was open, but now I would guess that it should be the resistance of the thermistor (1.0-1.6 MOhm).
 
Third and last iteration for the rubber roller fix.
I just removed the original (?) rubber sleeve and replaced it with 4 rows of 2 silicone rubber bands overlapped, in order to reproduce the correct thickness.
Important: the felt pad on the paper tray is essential to keep the paper level. Else, the paper will curl and jam in the printer.
So, as in my unit it was damaged, I just rebuilt it using some felt.
Printer now works like a charm, both cassette feeding and manual feeder.
The wiper blade in the cartridge is in a bad shape, so there are still some hair thin horizontal lines, but I can live with that (also because I would not know where to source a replacement…).

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This short video is showing the start up phase.
Before recapping only the fan would spin.

 
Wow, that takes forever to boot. I won't complain about mine with a harddisk crunching along.

I have ordered the replacement parts now and will get back to this thread in 2-3 weeks.
 
Hey all, my parts arrived. I replaced the thermoswitch, pickup roller and expeller gear. Unfortunately it still behaves the same as before the thermoswitch replacement (the lamp is still not glowing it seems), but there is continuity now at the J-112: Around 5-6 Ohms before I turned it on.

No idea if it's supposed to be like that, it would be great if someone with a working printer could confirm a similar reading.

I'll go back to the service manual once more to find some clues :(
 
As long I as it's not needed to dismantle again my printer (I did it already too many times…), I will be glad to support you with anything I can do.
 
Thanks, but I guess to verify signals and voltages the printer needs to be with the covers off at least.

I checked the triac and it measures fine, there's also line voltage at the J-112 connector from the AC supply side.

Next I'm going to find a way to check the /RDY and /FSRD signals, and depending on the results I'll hook up a bulb to the AC output and/or line voltage to the lamp to see if it turns on respectively
 
Using a MO disk as the main boot disk wasn't a good idea (even if they were large capacity for the time). Don't some next machines have issues with the MO drives not working anymore?

The printer seems to work nicely in the video (nice and clean too), how many PPM is that model?

Not too many people bother fixing old laser printers anymore unless they are platform specific like the NEXT one.
 
Unknown_K said:
Using a MO disk as the main boot disk wasn't a good idea (even if they were large capacity for the time). Don't some next machines have issues with the MO drives not working anymore?
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Yes, surely not feasible for everyday use, even though marketing-wise it was advertised as the baseline option. But an expensive primary scsi drive was de facto a necessity.
Also because MO units were faulty and sensitive to heat and dust. 30 years on, all the MO drives need thorough refurbishment.
If you are lucky, it's a capacitor job, but not necessarily just that. In any case the replacement of the capacitors is a very tedious and difficult job per se, as there are indeed many of them to replace. I successfully revived 4 units out the 5 I attempted, so a fairly decent rate I am happy with.

Unknown_K said:
The printer seems to work nicely in the video (nice and clean too), how many PPM is that model?
Click to expand...

It is a 400 dpi unit (300 dpi also possible).

I bought the printer as junk, now it works nicely, thanks!
Only remaining issue is with the wiper blade, so a couple of hair-thin lines appear on the printed pages... still more than fine by my standards.
It's been a nice project that taught me a lot.
 
So, apparently my printer too has decided to abandon me.
Not using it intensively (what for?), last week I printed a few pages, then switched everything off normally.
At the next restart, though, it got simply dead quiet. Not even the relay in the AC power brick gets triggered.
Now, in fact, if I disassemble the whole thing, reset it, put it back together, the relay closes and then immediately opens up again.
So, I would say there must be something that got busted and is now shorting.
At close visual inspection of each board and component, though, everything looks fine.
The lamp seems also to be OK.
Would you have any suggestion where to start from?
 
How did you check your lamp? After I couldn't find any clues or proper service documentation on what is wrong on my printer I decided to banish it into the basement and pick it up sometime in the future.
 
Only check I did on the lamp is the continuity one, without disassembling it. It’s not open, so I assume it’s still OK.
I have identified in the manual a couple of “easy” checks which maybe connected to the power up step, in case they won’t reveal any further clue, I won’t waste additional time after it.
 
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