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Model 4 Drive Oddity

itripn

New Member
Joined
Jan 10, 2022
Messages
3
Hey all, I've just recently started collecting some of the computers that were around in the early to mid 80's, in particular those that my young, closed mind (I was an Atari computer fanatic back then) sadly kept me away from.

I have a fairly pristine 64K model 4 ( some shots here: https://www.instagram.com/p/CSfThbNBZil/ ) with dual drives. First, I am a software engineer, not a hardware engineer. I do my best, but lack some of the foundations that might make me more adept at repairing these wonderful machines.

I recapped the power supply, and did a thorough cleaning of all inside and outside surfaces. Drive 0 lights up and spins, but never seemed to recognize a disk. Then for some reason I decided to put some downward pressure on the upper spindle (the whole mechanism actually), and amazingly it started recognizing and reading disks. But only when I put this pressure on the closing mechanism that the top spindle is attached to. I can only do this of course when the case is off.

Looking at the mechanism it is not clear to me if there is a mechanical adjustment I can make to help with this? I've tried reading through any relevant service bulletins I could find, etc.

Has anyone had this issue, and if so found a way to remedy it?

Thanks,
Ron
 

ldkraemer

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Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Ron,
What is the Manufacture's name on your Floppy Drives? Tandon, MPI, Texas Peripherals, Other?

If they are Tandon's, with the floppy Door open, look for two Short, White, Nylon Pins in the Hinge
for the hinge point. If they were used it's likely you need a hinge part to repair the door assembly.
Hinge repair parts are available.

Do you have the capability to write a Floppy Image to a Real Floppy for the Diagnostics? You can use
Imagedisk Ver 1.18, Teledisk, SuperCard Pro, Linux's dd (writing a sector Dump = .RAW), a TRS080
Floppy Emulator (PC = Desktop) with a 5.25" Floppy Attached.

If you look at the Power Supply(s), if you have a Tandon Power Supply with a long row of Pins for the
LOAD Side Connectors, be sure to VERIFY that each pin of the Long Row of Pins has a good solder
connection. Those supply's were bad about having small rings around the pins were they had a bad
connection to the PCB. Reflow the Solder for each Pin with Kester 63/37 Solder. (I use .050 Diameter).

PM sent.

Larry
 
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ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Last edited:

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Ron,
I've attached a Photo of a Tandon's loading assembly, and I'd like to know how much lower you
have to move the assembly to get a good reading. If you depress the assembly at the RED Circle
do you move the center hub assembly .005", .010", or more to get the floppy to clamp the disk
and start working? (I ran into this same type of thing when we originally created the Hinge parts,
and I had my brother make the Hinge load the assemble load several thousandts deeper.)

Perhaps for that Brand drive you need a replacement hinge part that closes a bit more than
the OEM part does at 40+ years age. It would be interesting to have you try one of our replacement
Hinge parts. If needed we can make another Hinge part that loads the assembly .005", or .010" deeper
to cause the center hub to hold the floppy. Or you could cut a small piece of .005" or .010" shim stock
and put it on the bottom of the Hinge part (opposite the shown yellow side) as a test. Just be 100% sure
the Door is flat with the front surface of the floppy, and the metal fingers are forcing the floppy to be
fully loaded before the door closes. This is done with the two screws slightly loose while you juggle the
parts to the proper position for tightening. (I'd recommend NOT removing the Logic board if you do this. It
will be a tight area to work in but the logic board will prevent the head assembly from being forced
past it normal position. I've been there and done that.....luckly no damage was done.)


Larry
 

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itripn

New Member
Joined
Jan 10, 2022
Messages
3
First, thank you ALL for the thoughtful and supportive replies! One of the things I love about the retro community!

I've got a busy week at work this week, but I will disassemble this coming weekend and answer some of the questions posed and see if I can get a little more precise about how much I have to press down. I have a decent 3D printer so I could also try printing a shim or complete replacement hinge as well, although I am intrigued by @ldkraemer's comment that I can buy a replacement hinge -- where do I go for that?

Thanks again, and I'll get back to this thread this weekend.

Cheers,
Ron
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
If you can compare your Hinge part to my sketch, and make sure it will work I'll send
you a couple to test. If they don't work I'll get a couple produced that will make the
loading assembly close tighter, or use a sketch you produce of the differences to modify
the Original Version 2 part for your Drive.

Larry
 

itripn

New Member
Joined
Jan 10, 2022
Messages
3
Hey all, finally got around to pulling the unit apart to get some photos and videos of the drive closing mechanism: Click here to see some photos and videos. Note, depending on your connection speed it make take a moment to load the 3 videos in the middle of the table. Each image should be clickable to get the larger version.

@ldkraemer I believe my hinge part looks similar to your rendering above. I don't have feeler gauges, so I am not sure exactly how far, but you can see in the videos, I would estimate 5mm or more of travel. I tested again, and again it would only boot disks when I pushed down on the mechanism as shown in the video (I have a ton of good bootable disks). Do you think a slightly thicker hinge will work? Let me know if you need me to fully disassemble to get clear photos of the hinge itself.

Of course, taking it apart again caused another issue -- the monitor which used to work perfectly now has to be turned up in brightness so bright that the horizontal bright lines appear in order to see any of the text. Not sure if I have a bad cap on the monitor board, or... Working around that thing makes me very nervous, but I'll have to troubleshoot at some point.

Thanks all!
Ron
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Ron,
I didn't have much luck watching the .MOV video's. Debian's VLC wouldn't play them, and
my W10 Laptop needed some special codec. My brother created a .MP4 but it didn't show
much about the clearance.

Here is my Door Replacement Document.


Larry
 
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