Canon Typestar 6 soft-mod! - Page 1
Forum section: electronics / repair

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 04, 2025, 01:58:49 am
content: I have a vintage 80s electronic device—a Canon Typestar 6—that has a weak paper advance stepper motor. Unfortunately, the motor is discontinued, and its casing is welded shut, so I can’t open it up for repairs. It works intermittently, but it often misses steps and needs some help to function properly.The device runs on 6V, with an internal DC-DC converter that boosts it to 10V. However, even at 10V, the motor doesn’t operate reliably. My initial idea was to modify the circuitry to increase the voltage to 12V, but that would affect all other components in the device, potentially causing more harm than good.An alternative approach I’m considering is adding a 12V-14V booster and using a low-impedance emitter follower to increase motor voltage. Without a load, the boosted voltage spikes up to 24-30V at its peak, so the emitter follower would help level and limit the voltage—keeping the original 10V for most components while switching 12V or 14V for the motor.Would this be a viable solution, or is it a bad idea? The device isn’t particularly valuable or important, but it’s brand new and unused. I’ve heard that these stepper motors are a common failure point in these machines. Since the motor is already faulty, I’d like to try fixing it, even if it’s just an experiment.

author: coppercone2
author_rank: Super Contributor
timestamp: March 04, 2025, 07:59:22 am
content: I would cut open the motor with the appropriate rotary tool and then figure out how to close it, if there is room creativity is your limit.Being defeated by a small weld is not acceptable

author: Gyro
author_rank: Super Contributor
timestamp: March 04, 2025, 09:54:30 am
content: On the contrary. If you have checked that all windings are electrically intact (and their resistances match), and that there is no roughness or sticking of the bearings, there is nothing to be gained by grinding welds, destroying alignment and potentially introducing swarf. There is no practical possibility of re-magnetizing the internal rotor.I would look at the drive electronics. If it has a 10V DC-DC converter, it may be giving the correct output output steady state, but not necessarily during the stepping pulses. Are there any electrolytic caps associated with the supply to the driver IC? If so, I would try replacing them with decent low ESR ones and maybe increasing their value.Increasing the supply voltage further will probably improve things (assuming that you driver can cope) but will obviously increase the heat dissipation in the motor. This risks overheating and further loss of magnetization but might extend its life in the short to medium term. I would experiment with the drive electronics rather than things within the motor (ageing) that you cannot fix.P.S. Another possibility is to look for a similar sized motor (ebay) and adapt the mounting and shaft coupling to make it fit.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 04:52:46 am
content: Thanks for the reply,I measured the signal at the motor terminals and observed that, when the motor is off, the voltage is around 10V. When the motor is switched on, it drops to about 0.7V, which is the opposite of a typical motor driver situation. Even after increasing the input voltage, the motor still sees about 0.7–10V, and the signal is somewhat noisy. I replaced the capacitors in the 10V power path and upgraded the reservoir capacitors, but the problem persisted.I’ve confirmed that the windings are fine, and the motor works roughly 50% of the time. When it doesn’t start, I can nudge the shaft slightly, and it will run. My first plan is to increase the supply voltage. If that doesn’t solve the issue, I might use a Dremel to modify things, but I want to avoid that if I can, since there’s no going back after doing it. Besides, the motor only spins for about half a second each time, so I’m not too worried about damaging it with a 40% voltage increase.My main concern is whether I can boost the 10V signal to 14V with just a single PNP transistor. I want to use that transistor as a low-impedance switch to raise the voltage, because when I remove the motor load, the motor terminal reads over 20V. It seems the motor itself is clamping the voltage at 10V. I’ll run more tests and measurements to confirm these observations, but based on my previous findings, this is what I’ve seen so far.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 05:02:11 am
content: Sealing the motor isn’t really my main concern. I believe the windings are potted in some type of resin, so I’m worried about damaging the magnet wires when splitting the motor halves—or worse, cutting them with a rotary tool. The machine works most of the time, and I don’t actually have much use for it, whether it’s working or not. I’ll probably just give it to someone who appreciates vintage machines. Honestly, I’d rather have a 100% chance it works half the time than end up with a 0% chance of it working all the times!

author: BradC
author_rank: Super Contributor
timestamp: March 05, 2025, 05:12:05 am
content: Quote from: ErwinsCat on March 05, 2025, 04:52:46 amIs bearing / bush lubrication worth looking at?

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 06:01:54 am
content: I removed the mechanism and lubricated the bearings and bushings. When the shaft is pushed forward by about 0.01 mm, it always works. I considered creating a harness to push the motor shaft forward, but that’s a questionable solution: the contact between the shaft and harness would produce a lot of friction and quickly wear down the softer metal. Plus, maintaining constant tension isn’t really feasible.That’s why I’m thinking about overvolting the motor first. If the issue persists and really bothers me, I’ll open up the motor to investigate—there could be a problem with the gears or thrust bearings. However, the device is practically new old stock, so the motor bearings likely aren’t too worn.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 06:04:49 am
content: I've attached some waveforms from the motor's terminals, as well as two images showing the switch-mode power before rectification—one with the motor running and the other with it off.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 06:14:45 am
content: Here are some more pictures. The little silver motor is the faulty one. I have to say, the board smells like the '80s—100 times over! It feels so nostalgic, bringing back good old memories. And yet, I’m pretty sure it was made with some of the most horrible chemicals you could imagine!

author: Gyro
author_rank: Super Contributor
timestamp: March 05, 2025, 09:14:39 am
content: Ah, those photos make things a lot clearer. The motor is driving a worm gear, which puts a lot of end thrust on the motor shaft, particularly if the gear teeth are getting worn and running dry.The motor shaft seems to be sticking out much further (towards the front of the Typestar) than I would expect, so it is a fair bet that it has worn down the internal thrust bearing to the point that the rotor is catching. You should find that the motor shaft has a fair amount of axial movement if you push the end with a screwdriver.It looks very possible to construct a simple thrust block to support the end of the shaft - a piece of hardwood, tufnol, nylon, brass, PTFE etc. - anything softer than the shaft, glued (or taped initially) to the base of the case and wedged by the plastic flange that supports the DC input jack. Maybe even a small screw through the base. Dimension it so that it takes up about half of the current end-play of the shaft. Add a drop of oil or grease and it should outlast the rest of the unit without any electronic mods.P.S. A small right-angle bracket with a brass screw and two adjusting/locking nuts might make a convenient adjustable thrust bearing.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 12:37:51 pm
content: By "front of the typewriter," do you mean the opposite side of the worm gear? Regardless, the movement of the shaft is very minimal—probably less than half a millimeter, perhaps around 0.2 millimeters.I placed a magnet with a hole in the center over the shaft, then added a full flat magnet on top of that. This slightly pushed the shaft towards the worm gear, allowing it to run without interruption.My question is: if this motor is worn, how is that possible on a machine with such low usage? It has probably been used for less than a single page since it was purchased, and it has been stored in its case for 40 years due to a blown fuse. The owner mentioned that the fuse blew the second time they used it…

author: Gyro
author_rank: Super Contributor
timestamp: March 05, 2025, 01:33:09 pm
content: That's an interesting solution!Yes, I did mean pushing towards the worm gear. The shaft just looked to be sticking out a bit further than I expected on the end opposite the worm.Those tiny steppers have minimal internal clearance anyway. Just one thought, the worm hasn't slipped along the shaft and started interfering with the end of the motor (or anything else in the gap)?It looks as if something to push on the non-worm end of the shaft should get it working anyway. Maybe just put a little tape over the magnets to stop them migrating!Just one other thing, if you were to grind off those welds, you would never get the motor aligned again. I would abandon that thought.

author: ErwinsCat
author_rank: Regular Contributor
timestamp: March 05, 2025, 01:47:49 pm
content: Thanks, mate! I'll keep it like this for now. I might get a bigger donut magnet to fit over the brass part completely and cap it again with another magnet.That cap magnet actually comes from a cochlear implant—it has a titanium cover all around. It was scrapped because the weld failed during testing, so it's got plenty of wear resistance. If I can get a bigger donut-shaped magnet, I should be able to attach them securely.I was also thinking I could sand down the donut magnet if needed to get the perfect spacing and just the right amount of force to do the trick. I’ll probably use some silicone adhesive to keep everything in place so it doesn’t move around all willy-nilly.