Definitive thread on Floppy Repair?

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greg christie

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Feb 20, 2020, 12:55:46 PM2/20/20
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Hi,

I’ve had a Cat for a few years - after reading about the floppy issues I’ve just left the one floppy in it.

I’m thinking about doing the needed floppy repair soon. About every six months or so I go through this group looking for documentation on how to do the repair but never seem to find anything definitive.

Are there clear instructions somewhere that I can never find?

Thanks in advance

dwight

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Feb 20, 2020, 1:37:05 PM2/20/20
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Hi
 I think Rubin has some pictures of the drive apart. I don't know if we have anything on getting the drive out. What fails is the clamp for the guide rail. It is a piece of nylon that was over stressed in the assembly. Nylon ages and become brittle and it cracks. In a few cases, I've seen it is just getting ready to fail. In others the tip has completely broken off.
What happens then is it lifts up at the back end when the disk is ejected. The being towards the front tilts down and catches on the floppies case. If forced, by pulling hard on the disk, one rips the head off, making the drive useless.
I replaced the piece with a tougher piece of plastic on mine. Jack just used some JB Weld epoxy to hold it down. Either way would work but be sure to limit where the epoxy goes. The heads guide slides really close the where the piece of nylon was.
As I recall disassembling the case is a pain. One will want to also remove the keyboard. I recommend loosening the main board by the screws on the bottom so you can get at the front of the board. You'll be able to access where the keyboard connects to the main board easier. The drive has a ribbon cable permanently attached but the board end uses a IDC type header connector. These are really hard to get loose and sometimes it is easier to loosen the side of the main board, with the floppy bracket loose first, to unconnect it. It is much harder to reach through the hold and one could easily pull the IDC of the ribbon apart from above.
Once you have the drive out, you can remove it from the drive bracket mount.
Pop the cover off and then you need to disassemble the top piece. As I recll, you can slide it forward some and the 4 pins will release it. Note how the eject spring works. As I recall, one has to hold it back while putting the top piece back in. With the top piece out of the way, you can see the back end of the head guide rail.
You'll find attaching the cable for the keyboard is much easier with the main board dropped down a litttle. It is one of the flex cable connectors and is solidly attacked at the keyboard end.
While you have things loose, is a good time to replace the coin cell for the CMOS RAM. I recall it is either a 2032 or a 3032 in a holder, towards the front of the main board.
Dwight



From: cano...@googlegroups.com <cano...@googlegroups.com> on behalf of greg christie <californi...@gmail.com>
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Subject: [Canon Cat] Definitive thread on Floppy Repair?
 
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Charles Springer

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Feb 20, 2020, 2:49:59 PM2/20/20
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For some reason, every time a promise to send someone the drives I have, I never do. They are NIB and maybe I should use one to get dimension (if they have the right part) and see about making or printing some replacements. Maybe use Delrin.

dwight

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Feb 20, 2020, 4:21:59 PM2/20/20
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Hi Charles
Delrin is nylon with some teflon mixed in. It gets brittle with age, like nylon does.
A small metal spring would be best. There are two holes to locate the piece. One hole has a pin that goes through the mounting and the nylon is staked there. The other hole has a screw to clamp it to the mounting.
The best would be a small piece of spring metal ( not steel though ) with a hole for the screw and a dimple to locate in the hole.
A delrin piece might still work but it doesn't need to be mounted flat to the mounting. It looks like the original design was that the screw would be tightened just enough to hold the guide rod. Someplace in the manufacturing flow, it must have change to completely tightened. This puts a lot of stress on the nylon finger that holds the rod.
The piece is quite small and would be a challenge for most 3D printers. The original looks to be injection molded.
Dwight



From: cano...@googlegroups.com <cano...@googlegroups.com> on behalf of Charles Springer <charles....@gmail.com>
Sent: Thursday, February 20, 2020 11:49 AM
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Subject: Re: [Canon Cat] Definitive thread on Floppy Repair?
 

Charles Springer

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Feb 20, 2020, 6:33:29 PM2/20/20
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How about Lexan? I have a lot of thick Lexan meant for 727 outdoor windows.

dwight

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Feb 20, 2020, 7:25:21 PM2/20/20
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It is mainly a problem of spacing it so that it isn't under stress. It was about 1/8 inch long finger bent at about 20 degrees. Truly, not a good idea. A piece carved out with a ledge to have light pressure would likely work. Anyway, you need to open it up and see what I was talking about. To get the staking loose you have to remove the PCB and scrape of the mushroomed end of the pin that goes through the mount. Just removing the screw isn't enough to get the remaining piece of of the way. That is not a problem for epoxying it down. You can just leave the piece in there.
Dwight


Sent: Thursday, February 20, 2020 3:33 PM

California Electric

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Feb 21, 2020, 1:35:27 AM2/21/20
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All, thanks for the details.

I think I need to see the mechanism to truly understand it all. I’ll post pics so this can get documented moving forward.

Hope to dig into it next week.

California Electric

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Feb 21, 2020, 8:52:54 PM2/21/20
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Okay, early start on this. I guess I’m motivated.

Will post pics as soon as I figure out how - it doesn’t look like the mobile version of google groups lets you.

I got access to the FDD by:

1 - invert cat on towel on workspace.
2 - remove 5 screws on bottom pan
3 - gently ease up one edge of pan giving access to the three cable connections. Watch the connectors at the rear of the cat.
4 - gently remove white flex cable from logic board
5 - ease the pan and logic board side over side from the edge without cable connection (visualize the two remaining cables as a hinge). Continue to hold the side of the pan with one hand as you remove the two cable connections. Note the direction of the 9 pin heavy header. Yes it’s keyed with a missing pin, but why risk bending anything.
6 - put pan aside.

NOTE - the FDD is NOT on a flex cable, at least not on my cat. It’s a standard ribbon cable. It’s captive on the floppy side but just a standard 20-pin IDC connector and header on the logic board side. This bodes well for making an adaptor cable for a floppy emu later. The flex cable is for the keyboard.

7 - roll the cat right side up.
8 - remove 4 screws from rear of cat. Two are mildly hidden in the handle area.
9 - Set aside rear case.
10 - remove three screws securing FDD bracket to frame. Note the larger screw is in the lower forward position.
11 - Ease the bracket with FDD off of the cat, being careful not to scrape the cable on the sharp edge of the frame cutout.

NOTE - either the insulation on the cable in the area where it passes through the frame should be reinforced OR the sharp edges of that cutout should be taped. My cable shows some evidence of abrasion in that area.

12 - Set aside cat
13 - Remove four screws holding FDD to bracket. On mine two opposite corners were thread locked - be careful not to strip the soft metal screw heads.
14 - Set aside bracket

Now you have the FDD with captive cable.

More to follow.

California Electric

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Feb 21, 2020, 11:24:29 PM2/21/20
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Okay, for documentation purposes here are the manufacturing details on my floppy:

IMG_6874.jpg


Also it's possible to get at the floppy just by removing the four screws on the back and pulling the back case, but the header for the floppy is directly under a cutout in the frame, and surrounded by a few caps, so it might be easy to slice your fingers on the frame metal. By dropping the pan and logic boardyou have much better access to the cable end without sharp metal around it.


California Electric

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Feb 22, 2020, 3:31:12 AM2/22/20
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Continuing with disassembly...

15 - Remove the 4 tiny tiny screws that attach the thin aluminum covers to the FDD.

So at this point I was able to gently eject the floppy I had in the drive. I did hold the head guide rod in place as I eased the disc out, just in case the drive decided to break at that moment.

Time for pictures and a question or two.

It seems that there are three points of interest regarding this guide rod. Closest to the front of the drive, the guide rod dead-ends into the metal platform for the disc:

IMG_6876.jpg


You can see it, just to the right of the head. There seems to be a bit of excess lubricant right on the end of the rod, but it's interesting to see that rod is not secured at that end in any way.


Now following that rod towards the back of the drive is a plastic (nylon? it sure is slippery stuff) finger. There is a matching finger on the underside of the rod. Here is a pic of the top side showing that finger secured by a shiny screw:

IMG_6878.jpg


The fingers top and bottom are close to the center of an inserted disc, just past the end of the travel of the head assembly. But I don't think those are the plastic tabs described in other threads as breaking, but I wonder if they should be reinforced as well.

Now, closest to the back of the drive is the plastic (again, nylon?) finger or tab that I think is the one that has caused so much trouble. Pic from the top:

IMG_6875.jpg


Nearest the top of the picture, just below the three caps, with the shiny screw, and seems to share mounting with the optical interrupter for track 0. Here's a slightly out of focus view from the back of the drive, showing the angle, and how it overlaps the double L shaped piece of identical material:


IMG_6880.jpg


So, Is that the tab that breaks and lets the guide rod shift? If so, what is the goal of the application of epoxy? Are we trying to fix the rod in place? Or trying to reinforce that plastic tab? Am I trying to loosen that tab, apply epoxy in the gap formed by the tilt and overlap and retighten? Epoxy across the top of the two nylon parts effectively tying them together into one piece and reinforcing the top part? All of the above? It looks like there is just enough room to do this while allowing full travel of the head along the rod. This is very slippery nylon like plastic and typically epoxy does not bond well to stuff like this. I can use a scalpel and micro file to roughen the surfaces to hopefully give the epoxy more grip. I agree with the others who think this assembly stinks. I would so much rather have metal circular retainers on BOTH ends of the rod, secured to the frame by screws.


Please let me know if I've identified the correct part (there's no visible evidence of a crack yet), and provide any input you have with regard to what to epoxy, etc...



dwight

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Feb 22, 2020, 11:13:26 AM2/22/20
to California Electric, Canon Cat
I see from your pictures that you didn't remove the tray assembly. I found it hard to work on that area without removing the tray or holder assembly. That is the tricky part I talked about earlier.
Dwight


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California Electric

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Feb 22, 2020, 11:49:58 AM2/22/20
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No, I haven't removed anything further yet.

Is that the correct part? 

What parts am I trying to bond with the epoxy? Or am I just trying to reinforce the top surface of it?

California Electric

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Feb 22, 2020, 1:33:47 PM2/22/20
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Just to be crystal clear, iis the suspect part this, in the middle of the guide rod:

IMG_6878.jpg

Or this, at the back end of the guide rod:

IMG_6875.jpg

It seems from the previous threads that folks are talking about the one in the second photo, at the back of the guide rod. But in the 2017 thread, "New Cat Repairs" by Marcin Wichary it seems that the tab at the back end is fine, but the tab in the middle of the guide rod is what snapped.


Thanks for any and all advice and details....


dwight

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Feb 22, 2020, 1:48:37 PM2/22/20
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I'm not able to open your last two pictures.
Yes, it is the finger with the screw.
As for what you'd want to do, imagine that the finger wasn't there and you needed to hold the rod down. You'd want to have epoxy all the way around the rod. Just putting epoxy across the top of the finger would be useless as if the finger fractured, it would just pop off the plastic. The stuff tends to sag a little when first put on so might be better as a couple of thinner layers than just a single application.
As for the epoxy, I don't recommend the norm junk you get at the drug store. Use 24 hour setting JB Weld. The stuff really hardens hard. It uses a metal filler.
Dwight


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California Electric

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Feb 22, 2020, 1:57:38 PM2/22/20
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Thanks, I'm sorry the last two images couldn't be opened. Let me try again in lower res, since both parts I'm asking about have a screw going through them. Perhaps my drive is slightly different to others?

One part is at the back of the drive, at the end of the guide rod:

back.jpg



the other part is towards the middle of the drive, in the middle of the guide rod:

middle.jpg


Both have shiny screws going through them.


Thanks again!


California Electric

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Feb 22, 2020, 8:17:42 PM2/22/20
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I noticed that there is some lateral play in the guide guide rod. I have to imagine that it was intentional, perhaps to compensate for poor centering of manufactured floppies. So I became concerned that any epoxy based solution would lock that rod too tightly perhaps causing additional problems. Also the tabs on my drive are intact, so surrounding the rod with epoxy would have been non trivial.

What I did was fashion a pair of aluminum straps the same size and rough shape of the plastic tabs:

part.jpg


I used industrial CA as a bonding agent to secure the nylon tab to the metal frame they rest on, and some more on the top of the tabs to laminate them to  the aluminum straps. The aluminum stock was think enough so that I could use the existing crews to secure them


Here they are installed:


brackets.jpg


The straps don't interfere with the drive head assembly or any other mechanisms, and clear the guide rod completely.


I've tested the drive with two separate floppies. All good so far (knock wood).


With the straps in place, I am considering a bead of epoxy across the top to provide extra mass and further rigidity to the reinforced tabs.


To finish out the disassembly steps:


16 - Release the spring wires from the left and right sides of the drive.


17 - Remove the large spring from the top of the drive


18 - jiggle the top tray forward and back a bit, trying to clear the black plastic catches and arms.


19 - remove screw and the black plastic block on the right, near the black hook shaped part and the pivot for the metal arm (where you removed the large spring). Note that the block is mounted both insde and outside the frame of the drive. It will need to go back exactly the same way.


20 - jiggle the top tray forward and back a bit, the pins on the sides need to come out of the slots, at the time that the central U shaped "fork" needs to slide out of the drive head assembly.


21 - Repair or reinforce the plastic tabs securing the guide rod as you see fit.


Reassembly is the reverse of the first 20 steps.



Thanks all.  Hope this description shows up in Google for the next person who needs to repair or protect their Cat.



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