IIfx won't read 800k disks made on other machines

[willmurray461]

I have a really strange issue with floppies in my IIfx. For some reason, the IIfx will read 1.44MB disks fine, but will only read some 800K disks. It reads 800K commercial software disks, as well as 800K disks that were formatted on the IIfx, but it won't read 800K disks that were formatted on another machine. If I format an 800K disk on the IIfx and then put it into another machine, the other computer will read the disk fine. At first I thought it was a head alignment issue, but if I take the same drive and put it into another mac it has no issues so I'm pretty sure the problem is with the motherboard.

The machine's orignal SWIM chip was dead so I swapped in one from a donor board. However, I never tested the chip so there is still a possibility it's still the SWIM's fault.

Anyone have any idea what could be going on?

 

[LaPorta]

It is possible that the head is ever-so-slowly dying on the drive of your IIfx. Only thing I can think of. Alignment would throw all disks off.

 

[willmurray461]

It is possible that the head is ever-so-slowly dying on the drive of your IIfx. Only thing I can think of. Alignment would throw all disks off.

I don't think that's the case because when I take the drive and attach it to another mac, it works fine. Likewise, if I take a drive from another mac and put it in the IIfx, it suddenly exhibits this issue.

Because of this, I'm almost certain it has to do with something on the IIfx's motherboard.

 

[nathall]

Well, the difference between 800k and 1.4MB disks is that the rotation speed varies on the 800k. You might be right about the SWIM chip, but could it also be a voltage issue on the IIfx? As in, not being regulated properly for the differential speeds needed for 800k?

 

[LaPorta]

I don't think that's the case because when I take the drive and attach it to another mac, it works fine.

I didn’t realize that, I missed that part in your first post. Did you try and source a replacement SWIM to rule out chip issues?

 

[willmurray461]

Well, the difference between 800k and 1.4MB disks is that the rotation speed varies on the 800k. You might be right about the SWIM chip, but could it also be a voltage issue on the IIfx? As in, not being regulated properly for the differential speeds needed for 800k?

The IIfx did have an incident where the 12V line on the PSU got shorted for a few seconds due to a faulty tantalum capacitor (which promptly caught fire and exploded). It may have caused damage to other components. Do you have any idea where to look in order to test the voltage theory?

I didn’t realize that, I missed that part in your first post. Did you try and source a replacement SWIM to rule out chip issues?

The original SWIM wouldn't read anything. I then took a SWIM off of a battery bombed IIci donor board, which leads me to where I am now. It's possible that the donor SWIM was also damaged, though I think the odds of that are very low.

 

[LaPorta]

Did the original SWIM IIfx machine have damage somehow? Why was the original SWIM bad?

 

[Fred1212]

Have you tried a known working drive in the IIfx? Do you get same problem? Oh I should read above posts you have done this so its a board issue. Another SWIM to be sure

 

[nathall]

The IIfx did have an incident where the 12V line on the PSU got shorted for a few seconds due to a faulty tantalum capacitor (which promptly caught fire and exploded). It may have caused damage to other components. Do you have any idea where to look in order to test the voltage theory?

I do not, unfortunately. Just seems like the road I’d go down to investigate if I had your symptoms.

 

[willmurray461]

So I've since acquired a second IIfx motherboard, one which is pristine and has never seen abuse. The second IIfx motherboard exhibits the exact same behavior with 800k floppies. As such, I'm inclined to believe this is just a quirk of the IIfx, as I find it extremely unlikely that two boards would have this same exact fault.

 

[Arbee]

Just to clarify: if you put the drive from the IIfx in another machine with the same exact disk it won't read in the IIfx, it then can read it?