Apple IIc - Writing to floppy disk impossible

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Apple IIc - Writing to floppy disk impossible

Hi,

 

I have a problem with my Apple IIc, it works very well except that it is always in write protected. Impossible to save even a file under DOS 3.3 or Prodos

I also tested with a SDCard floppy emulator, same problem. 

 

No problem with the floppy SDCard emulator on my Apple IIe, I can save a file.

I checked the track between the IWM and the connector, everything is ok.

I'm starting to think that the IWM might be the cause of this error.

 

Thanks in advance for your help

 

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More than likely it's an

More than likely it's an issue with one of the chips on the drive control board. Most likely the 74LS125. They are cheap and readily available. 

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I'm afraid, if you already

I'm afraid, if you already verified that the issue happens with the original drive, as well as with a known-good replacement (a floppy emulator) then it's pretty obvious the issue is on the Apple IIc side - not a broken drive. And as you already saw, on the Apple IIc the WRPROT signal goes directly from the connector to the IWM chip. There is nothing in between. And you already verified the trace has continuity from IWM to connector. That leaves little, to almost no hope for another issue - except that the IWM is bad.

An issue on the databus side of the IWM is extremely unlikely, since everything else works fine, as you say, even reading disks.

The only other "hope" for a simpler issue would be an issue with the connector itself. Plug the drive (or the floppy emulator) and verify continuity of WRPROT from the IWM to a pin on the drive itself. I've seen connectors which seemed fine (when probing from the connector pin to a chip on the board), but if you plugged something in, it just wouldn't make proper contact - so a connection was broken after all. It's an unlikely but ugly case (though easy to fix).

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Thanks for your answers, I

Thanks for your answers,

 

I tested with my Internal/External Drive Switcher, same problem. Reading is fine, but not writing.

So the IWM has a problem, I did a quick search, I don't think it's very easy to find one. I also did not see any solution to replace it with one or more circuits.

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Unfortunately the IWM is

Unfortunately the IWM is essentially unobtanium as it was an Apple custom ASIC which hasn't been made in years.  Your only source for one would be a donor machine.  They were used in the //c, IIgs,several of the early Mac models and some other Apple products like the LiRON and the //e card for the Mac LC.  Non-working Mac or IIgs motherboards may not be the best source of donor parts because I think a lot of them may use a different package than DIP.

 

It would be possible for someone to create a modern replacement for the IWM using a CPLD or FPGA, but as far as I know nobody has made anything that is a drop in.  However, several people like Steve Chamberlain of BMOW have done a lot of the work for projects like the Yellowstone floppy controller.  What someone would have to do is cut the necessary logic out of the FPGA code and then design a chip carrier which would fit into the socket for an IWM and provide the glue to connect the FPGA core (most of which are 3.3V) to the 5V pinout.  This kind of thing is possible because other projects have done it for example there is a replacement for the AY-5-3600-PRO keyboard controller from Joe's Computer Museum and a 65C816 replacement from A2 Heaven.  It is probably more challenging in the case of the IWM because of size.  The IWM chip is a 28 pin package and most of the modern replacements that I know of have been developed are for larger 40 pin packages where there is more space for things like voltage regulation and level shifting.

 

Two other chips it would be useful to develop CPLD or FPGA based replacements for would be the MMU and IOU chips as used in the //e and //c.  Those are also unobtanium.

 

If replacements were avaialble for the IWM, IOU and MMU chips it would pretty much be possible to make entirely new //e and //c motherboards.

 

 

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So, for the moment no modern

So, for the moment no modern solution to replace the IWM

I read somewhere that the 344-0043 of the MAC SE should be compatible with the 344-0041 of the IIc.

My new goal, find a MAC SE motherboard out of order, if I find one, I will post the result

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Make sure that the SE

Make sure that the SE motherboard uses the DIP version of the IWM.  A lot of other Macs and the IIgs use a package with pins on all four sides.  To use one of those you'd have to make some kind of adapter.  And there isn't a lot of room in a //c for things like that.

 

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