Testing Apple Disk ][ Interface card?

6 posts / 0 new
Last post
gmc
Offline
Last seen: 3 weeks 3 days ago
Joined: Sep 29 2021 - 08:41
Posts: 15
Testing Apple Disk ][ Interface card?

I've got a Apple IIe which came with a Disk ][ interface card. (With the 2 x 20 pins connectors)

 

I've also bought a Disk ][ Floppy off eBay which was sold as faulty. It would not spin up  and after testing all the chips I found a dead chip on the speed controller board.  Replaced and the drive appears to work in that it does all the right actions, but I cannot read/write any disks.

 

My issue now is I'm not sure if its the floppy drive, or the interface card that is faulty. I'm beginning to think the interface card as I've also built a sdisk2 and can't get that working either.  (But it could be a case or either/or both being faulty)

 

Is there any standalone testing (maybe with some kind of looback connector) I can do on the interface card to first make sure that is working as expected (The obvious test would be to test it against a known good floppy, but there lies the problem)

 

I've tested all the logic chips on the interface card and they all work fine. Nothing is getting warn on the card either.

Offline
Last seen: 10 hours 17 min ago
Joined: Apr 1 2020 - 16:46
Posts: 476
First thing to do with faulty Disk II drives ...

... change the 74LS125. This IC usually gets destroyed when the 20-pin header is plugged into the "other" style of Apple II disk sockets that can be found i.e. in the Apple IIc.

 

If this does not help, replace all the electrolytic capacitors.

 

This is about as much as you can do without an oscilloscope and some other items found in a well equipped electronics lab.

 

- Uncle Bernie

Offline
Last seen: 14 hours 16 min ago
Joined: Dec 20 2003 - 10:38
Posts: 509
On the Disk II card the PROMs

On the Disk II card the PROMs have been known to die. Also the  capacitor sometimes go bad. If you post your location, maybe there’s someone locally with a good card and drive willing to help.

gmc
Offline
Last seen: 3 weeks 3 days ago
Joined: Sep 29 2021 - 08:41
Posts: 15
On the interface crd I've

On the interface crd I've tested all the logic chips as well as the transistors - all good.

 

I've also built a arduino jig to read and compre the proms - all test good there.

The only thing I haven't been able to test yet is the NE556 chip. I guess I could take it out of circuit and build a time circuit on breadboard to see if it's working.

 

On the disk drive, I have also tested the 74125 - all good, but replaced it anyway. Tested all other logic chips, diodes, transistors. Guess I could replace the caps and hope for success.

 

Supply rails on both boards are present and good.

 

I've got access to a digitcal scope, logic analyser and a bunch of other tools if that helps and someone can point me in the right direction. 

 

I'm in the UK - North West.

 

 

 

MacFly's picture
Offline
Last seen: 3 hours 41 min ago
Joined: Nov 7 2019 - 13:49
Posts: 182
gmc wrote:I've got access to
gmc wrote:

I've got access to a digitcal scope, logic analyser and a bunch of other tools if that helps and someone can point me in the right direction.

 

Well, that should help... :)

Start by probing the RD DATA signal. This is the raw "magnetic flux" signal returned from the disk II drive to the interface card. When the drive is spinning and a disk is present, you should see the signal toggling at TTL level all the time. When no disk is loaded, the signal is constant (even when the drive is spinning). If the signal is dead with a good disk spinning, then you need to invesitgate the drive itself (broken r/w head or dead drive electronics).

If you do see a toggling TTL signal, you can make a simple test of the interface card.

Enter the monitor. Then enter:

  C0E9:00

to switch on the drive 1 motor. Now the disk is spinning.

Then repeatedly read the disk II interface's read latch (just enter "C0EE<RETURN>" and the monitor will show the current value of the disk read latch):

  C0EE

  C0EE

  C0EE

  C0EE

When a disk is spinning, you should see changing values. Then stop the motor by entering

  C0E8:00

and, again, read the C0EE latch repeatedly. When the motor is stopped, the read latch needs to return constant data (whatever data was in the latch last, will no longer change).

If these register tests do not behave as expected, but you did see a toggling TTL signal from the disk II drive, then you clearly have an issue with the interface card (bad address decoding logic, dead P6 PROM or shift register IC).

If the register tests do work, then this still leaves a number of options (bad disk, misaligned drive head to a bad (but not completely dead) P6 PROM)...

Offline
Last seen: 20 hours 18 min ago
Joined: Apr 26 2016 - 08:36
Posts: 387
Take it back to the basics.

Take it back to the basics.

 

Can you verify the speed of the disk drive?  That would be the first thing to check if your drive isn't reading or writing.  Especially since you changed components on the spindle motor circuit board.

Next I'd check the physical connection to the read/write head connector and the analog board on the drive itself.

 

Have you tried an analog board from a known-good drive to see if the issue is there?

 

Next I'd tackle the drive's alignment, but only if you can get the speed correct.  You can adjust the drive speed under a lamp using the stobe disc on the drive spindle for a rough adjustment and then dial it in using some diagnostic software (most Apple II diagnostic software tools like Apple Cillin and Aptest have some sort of drive speed check)

Log in or register to post comments