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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 8th Apr 2024, 4:23 pm   #121
TonyDuell
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Default Re: Commodore 8026 printer / typewriter

And here's the last part of the schematic, the keyboard. It seems to make sense and agrees with that of another Olympia typewriter.

Thanks to Colin for taking the time to trace all the connections.
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Old 8th Apr 2024, 5:29 pm   #122
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

Thanks so much to Tony. I would not have been able to do this at all. I'm very grateful.

Onto the broken cog - broken in three places.

90 teeth
4mm thick
46.5mm in diameter (although this has to be a guess as the cog has clearly shrink over time
Each cog is 1.2mm high

The cog is somehow attached over the metal centre part so unless I can think of something different, I may have to glue one onto the metal part one one side only.

Colin.
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Old 8th Apr 2024, 5:40 pm   #123
TonyDuell
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Default Re: Commodore 8026 printer / typewriter

Hmm. Old engineer's rule of thumb is that the 'module' ~= diameter/(no of teeth +2). In your case this sounds very much like a module of 0.5. A 0.5 module 90 tooth gear is almost certainly a standard part.

You would have to modify the hub of the replacement gear to fit the spindle. A trivial job with a small lathe, but I guess you don't know anybody with one.
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Old 8th Apr 2024, 5:52 pm   #124
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Default Re: Commodore 8026 printer / typewriter

I'll start with the 90 tooth design here and work in it.

https://www.thingiverse.com/thing:683030/files

Colin.


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Originally Posted by TonyDuell View Post
Hmm. Old engineer's rule of thumb is that the 'module' ~= diameter/(no of teeth +2). In your case this sounds very much like a module of 0.5. A 0.5 module 90 tooth gear is almost certainly a standard part.

You would have to modify the hub of the replacement gear to fit the spindle. A trivial job with a small lathe, but I guess you don't know anybody with one.
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Old 8th Apr 2024, 7:09 pm   #125
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Default Re: Commodore 8026 printer / typewriter

OK - I need to wait overnight for this to cure then it'll be time to get the old one off and see.

Colin.
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Old 8th Apr 2024, 7:23 pm   #126
SiriusHardware
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Default Re: Commodore 8026 printer / typewriter

Incredible how you can come up with a first prototype like that so quickly. I think the thing I notice about it immediately is that the teeth / cogs are less deep and less sharp than those on the original item.

I had a new gear printed as a replacement for one of the 'cheese' gears in an old Philips radio / cassette recorder and unfortunately it wasn't a great success because the teeth were too shallow and too blunt, so it will be interesting to see how this one goes.

I'm also interested to see if the underlying metal disc has some kind of index bumps or holes in it, otherwise I can't really see what would prevent the plastic gear from slipping / rotating independently of the metal disc.
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Old 8th Apr 2024, 7:53 pm   #127
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

Nothing obviously holding it on; perhaps it was heat shrunk on or maybe glued.

I'll be very pleased if my first version works, but not surprised if it needs some tweaking yet.

Colin.
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Old 9th Apr 2024, 1:02 am   #128
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Default Re: Commodore 8026 printer / typewriter

I presume the filament material-type chosen for the 3D-printer, will have an impact on minimum feature size ? (We found this recently, with some bright-green PLA? on an expensive Ulimaker system, whereas someone said they'd got better results on their rather-cheaper home 3D printer - with their normal black, but presumably different?, material).

Of course the ultimate is maybe a (Laser?) fused system, that can do nylon or a sintered metal powder system that it seems can match wire(spark?)-eroding systems in making a strong and accurate part. But prices of these systems will be rather out of reach of the home user.
(Although maybe there are places that will print a part for you with these - I see JLCPCB offer a 3D printing service, but not sure what equipment they have invested in)
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Old 9th Apr 2024, 2:36 am   #129
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Default Re: Commodore 8026 printer / typewriter

Colin mentioned in an earlier post that he was going to try with a resin 3d printer, this was why he needed to leave it overnight to cure. I think the resin printers don’t use a filament.
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Old 9th Apr 2024, 9:19 am   #130
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Default Re: Commodore 8026 printer / typewriter

As Sirius said, I am lucky enough to have both a Prusa filament printer and a resin printer. I've printed this in resin as the detail is much better. I hope if I have the teeth the right shape/size, it's harder wearing too.

I could print on the Prusa with a smaller nozzle which allows for finer detail with PLA/ABS. Let's see how this goes.

The only thing that's troubling me right now is that to use this gear, I have to break the old one off, so it's a one way process.

I may reinstall the broken one for now while we're getting this working and look at replacing the whole component including the shaft later.

Colin.

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Originally Posted by ortek_service View Post
I presume the filament material-type chosen for the 3D-printer, will have an impact on minimum feature size ? (We found this recently, with some bright-green PLA? on an expensive Ulimaker system, whereas someone said they'd got better results on their rather-cheaper home 3D printer - with their normal black, but presumably different?, material).

Of course the ultimate is maybe a (Laser?) fused system, that can do nylon or a sintered metal powder system that it seems can match wire(spark?)-eroding systems in making a strong and accurate part. But prices of these systems will be rather out of reach of the home user.
(Although maybe there are places that will print a part for you with these - I see JLCPCB offer a 3D printing service, but not sure what equipment they have invested in)
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Old 9th Apr 2024, 10:45 am   #131
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Default Re: Commodore 8026 printer / typewriter

If you want to get an idea of what the metal disc looks like maybe you could warm the shaft and disc up a bit and then look at it with your thermal camera. The temperature difference between the disc and plastic gear might allow you to see any indexing / locating feature on the metal disc without first removing the remains of the plastic gear.
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Old 9th Apr 2024, 1:49 pm   #132
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

That's a good thought, but I tried it and there's nothing obvious holding it on.

Colin.

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Originally Posted by SiriusHardware View Post
If you want to get an idea of what the metal
disc looks like maybe you could warm the shaft and disc up a bit and then look at it with your thermal camera. The temperature difference between the disc and plastic gear might allow you to see any indexing / locating feature on the metal disc without first removing the remains of the plastic gear.
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Old 9th Apr 2024, 5:12 pm   #133
TonyDuell
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Default Re: Commodore 8026 printer / typewriter

I would always avoid using glue if possible. You never know when it will have to be taken apart. I would also avoid modifying anything I couldn't undo or re-make.

In this case I could make the spindle and metal hub if I had to. So I'd be prepared to make sensible modifications to them. I'd probably drill 3 holes equally spaced in the disk and use them to take screws to hold the new gear on.

The hub might have been pressed onto the spindle at the factory. I would be somewhat surprised if that was the case, I'd expect it to be possible to remove the gear/hub to replace it. Are you sure there's no fixing grub screw roll pin or similar?
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Old 9th Apr 2024, 5:30 pm   #134
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

I had thought the same. It's a 6mm rod so I was thinking of buying a length of M6 double end threaded stud bar and using some nuts with blue thread locker to hold the gear in place.

Let me think some more - that's (yet again) a kind offer.

No grub screw - attached is a photo from the end of the spindle to show what it looks like.

Colin.

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Originally Posted by TonyDuell View Post
I would always avoid using glue if possible. You never know when it will have to be taken apart. I would also avoid modifying anything I couldn't undo or re-make.

In this case I could make the spindle and metal hub if I had to. So I'd be prepared to make sensible modifications to them. I'd probably drill 3 holes equally spaced in the disk and use them to take screws to hold the new gear on.

The hub might have been pressed onto the spindle at the factory. I would be somewhat surprised if that was the case, I'd expect it to be possible to remove the gear/hub to replace it. Are you sure there's no fixing grub screw roll pin or similar?
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Old 9th Apr 2024, 5:33 pm   #135
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

I've found this web site which allows parameters to be enetered online to generate a design for various cogs/gears:

https://www.stlgears.com/generators/3dprint

There's also an app that can be added to Fusion 360 (my design tool of choice) to do pretty much the same:

https://apps.autodesk.com/FUSION/en/...ng=en&os=Win64

Colin.
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Old 9th Apr 2024, 9:55 pm   #136
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

OK - I have made a decision to temporarily put the original cracked gear back in place while I think about what to do with it.

Everything is now where it should be with the exception of the main PCBs. The print carriage is back in place with its PCB.

I have not connected any of the data wiring to the main PCB.

I have measured the PCB outputs and have the following:

Pin 2 (Grey ) - 10.55V
Pin 3 (Red) - 39.26V
Pin 4 (Brown) - 4.99V

Am I ok to re connect the PSU to the main PCB? Or do any of the voltages look sufficiently 'out' to you and will need further investigation?

Colin.
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Old 10th Apr 2024, 4:43 am   #137
TonyDuell
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Default Re: Commodore 8026 printer / typewriter

You were very sensible to check the power supply on its own.

Those voltages look fine. The important one is +5V which powers all the logic chips. If it's too high it could ruin the lot. But it's fine.

The other voltages are high as they are off-load. But they are not so critical. The nominal +36V powers the motors when they are moving, the +9V provides a 'holding' current to the stepper motors when things are not moving.
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Old 10th Apr 2024, 1:00 pm   #138
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Default Re: Commodore 8026 printer / typewriter

OK - next stage of the plan then is to plug the PSU connector to the logic board and check some voltages. There's a 39V testing point of the right hand side of the board (See page 2). Any other good places to prod around?

Colin.
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Old 10th Apr 2024, 4:57 pm   #139
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Default Re: Commodore 8026 printer / typewriter

Next logical step is to ensure that you have 0V and +ve supplies to each of the ICs. If you don't know where the supply pins for the ICs are (they may or may not be indicated on Tony's diagram) then find the datasheets for the ICs in question.

This may seem like an overzealous operation (if the +5V supply is present across one IC which runs on 5V is present then surely it follows that it will be present on all of the other ICs?) but in this case the board has suffered severe localised battery leak damage, and you can't assume anything.

Unless, of course, Tony already metered out every single track and via - which is the sort of thing one might do when trying to reverse-engineer the diagram?
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Old 10th Apr 2024, 5:29 pm   #140
ScottishColin
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Default Re: Commodore 8026 printer / typewriter

OK - earth wire plugged in and PSU connected.

Powered on and the buzzer buzzed for a while (c. 30 seconds) then went off.

I probed around and am reading 4.7V in several places including ICs on the smaller IEEE interface board and 36V on the test pin so that was a start.

Then I noticed that worrying electrical smell, so I took a photo with my thermal camera which shows that the BC327 was at near enough 200 degrees.

Followed by magic smoke from the bottom left 212-4.

So I've turned it off.....

Where should I start do you think?

Colin.
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