Kaypro 2X boot problem Oki drives

[jmellidg]

Hi folks,

I have an issue with a computer that I'm revising. It's a Kaypro 2X, with a ROM version 81-478A and motherboard ASSY 81-581. It comes with two DSDD floppys OKI GM3305 HU. I couldn't find anything about these disk drives in the Internet, by the way.

After change a exploded RIFA capacitor, the computer boot, but it can't read the cpm 2.2UL that is the version of cpm for this computer. After a couple of days testing a lot of things and doing a lot of system disks from different images , I manage to boot changing the floppy disk drives ( no one of the two okis work) for a good known toshiba.

As soon as change the drive, it starts at first try.

Well, I'm really surprised, because it seems to me normal that one drive fail, but two?? I've tested the oki drives in a clonic XT but don't work. Do you have any idea about what's going on or do you have any information about the oki drives??

I cleaned the head and try to lubricate the rails, but it's not easy, as you can see in the photo, the rails are inside a cilinder so I can't lubricate without dismount all the mechanism. In 2016 I had the same issue with this computer, but after select the correct version of cpm the computer works.


Thanks for your help

 

[krebizfan]

Which capacitor exploded? Does it have any connection to the floppy drives? My guess would be that whatever surge took out the capacitor also took out something on both floppy drives. Maybe starting with an examination of the capacitors near the floppy drive power connector might give an idea of what component failed.

The other component that goes to both drives is the floppy controller but I find it hard to believe a surge that passes through the controller and damages both drives wouldn't also damage the controller.

 

[jmellidg]

Hi, thank you for your answer, there was a rifa capacitor in the power supply, it's a very common failure in this old computers

 

[ldkraemer]

Adrain has a Video on the OKI 5.25" Floppy Drive.

Quick take: Fixing an interesting Okidata GM-3315BU 5.25" floppy drive - YouTube

I took a snapshot of the DIP Switch toggles and made the positions RED so they are
easy to see for "ON" and "OFF".

Your settings are incorrect as you have two drive select signals toggled.

DIP Switch has 8 Toggles.
1 OFF - Toggles ON the TERMINATION Resistor(s) - typically last drive on the Floppy Cable
2 OFF - Drive Select 0
3 ON - Drive Select 1
4 OFF - Drive Select 2
5 OFF - Drive Select 3
6 OFF - MX
7 OFF - HS (Head Load with Drive Select)
8 ON - HM (Head Load with Motor ON)

If you set the proper Drive Select in a DS{0..3) configuration and the remaining toggles as per
the attached Photo your Drive should work. (Assuming you are using a Floppy Cable for CP/M
with no Twisted Conductors (10-16).

The TERMINATOR should be "ON" for the last Drive on the Cable.

Larry

 

[jmellidg]

I have two drives with a plain cable, no twist. The first one in kaypro (drive A)

Termination off, DS0, hs on and hm off

The second one ( drive B)

Termination on, DS1, hs on and hm off

These are the original settings when opened the case

In a dos machine, with twisted cable

The first one in dos (drive A)

Termination off, DS1, hs off and hm on

The second one ( drive B)

Termination on, DS1, hs off and hm on

Do you think that are wrong??

Thank you for the video!!!

 

[ldkraemer]

jmellidg,
Those switch settings are correct, but that isn't what your attached Photo shows.

Larry

 

[jmellidg]

It's a picture of the B drive configured in the kaypro,

The second one ( drive B)

Termination on, DS1, hs on and hm off

 

[unlimitedbacon]

I'm having a similar issue with a KayPro II with exactly the same model of drives (Okidata GM 3305HU). The issue is intermittent, and the drives will actually boot occasionally.

I discovered that on a cold boot, the drive does not retract the read/write head to track 0. If the head is not already in the outside position, it tries to start reading from the middle of the drive. If I physically push the head back, it immediately starts to boot. The drive works normally afterwards.

I am at a loss for what is going one. Once the computer boots, the drive works normally. It just doesn't seek to track 0 on a cold boot. Moving the head by hand is obviously not ideal. Does anyone have any idea why this might be happening?

 

[ldkraemer]

Sure, I had a Kaypro 4 that was doing the same thing. It did not boot and I finally found that the head
wasn't stepping to track 0 because the FDC wasn't getting the /WE signal. Check that your are getting
the LOW signal on Pin 2 of the FDC (1793). In my case it was the 74LS32 that was defective.

What is the Number of your Motherboard 81-xxx? Use the Motherboard number to find the proper
Schematic for the FDC 1793.

1484-F_Kaypro_Technical_Manual_Sep85.pdf - Shared with pCloud

Keep, share and access your files whenever you need from wherever you are. Create a free pCloud account and make your life easier.

u.pcloud.link

Larry

 

[jmellidg]

Hi folks, I've fiddling again this days and I have exactly the main issue described by unlimitedbacon. I'm testing the drives in a DOS environment and for one drive, that was it happens. The other drive doesn't work at all but their problem is related too with the track position.

Both drives pass the David Dunfield's TESTFDC tests so apparently when there are in a good position work. Any clue related with the drives itself or you think it's a problem with the controller??

 

[Conventional Memories]

Hi folks, I've fiddling again this days and I have exactly the main issue described by unlimitedbacon. I'm testing the drives in a DOS environment and for one drive, that was it happens. The other drive doesn't work at all but their problem is related too with the track position.

Both drives pass the David Dunfield's TESTFDC tests so apparently when there are in a good position work. Any clue related with the drives itself or you think it's a problem with the controller??

I'm having the exact same issue with a very similar OKI drive GM-3305bu from an Ericsson Portable PC, the drive has issues returning the head sometimes and it refuses to find the first track. but after that it seems to work fine sometimes.
I think I have found the issue with all of these drives with the "linear motor" head drive. I tried lubrication, recapping, but neither of those things did anything, so I decided to open up the linear drive motor/mechanism.

Drive mechanism


linear head assembly taken apart

And here you can see the issue with these, the head assembly has a rubber bumper on the back that prevents the head assembly from slamming into the cylinder that houses it.
As you can see the rubber on this is completly disintegrating, with both harddened and melted pieces of rubber.
This seems to be the issue, and why the head somtimes binds and can't index to track 1


To test if this is fixable I cleaned the assembly and cylinder very well and put in a 1mm thick piece of rubber I had laying around, after reassembly and a drop of bearing oil I can put everything back in the FDD drive.
I don't have any experience with alligning 5.25" FDD's but I managed to do it well enough for testing.
And to my amazment this seemed to completly fix it.
PC boots everytime now, no more issues with reading anything, and the head doesn't get stuck anymore, and it now always returns properly.

This seems like a good fix. but the real annoyance is that you have to do a disk allignment after removing the whole head assembly.
Anyone have some tips on how to do this properly? Is that even possible without a allignment disk?
Any manuals on these OKI drives?
Does the fact that I can now read and write entire disks bethween this and another drive mean that it is alligned properly?

hope this can help anyone with a similar OKI drive issue.