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Attainable IWM replacement for Apple IIc using work around.

VERAULT

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Joined
Jan 30, 2012
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Connecticut, USA
So someone sent me an Apple IIc for repair. I dont know what happened to this thing but it has multiple faults all related to the floppy drive interface. The IWM has failed, the internal floppy drive analog board has failed, and something on the drive mechanism (I suspect the stepper motor) has failed. The only thing I can think of is a surge as the odds of these failing at the same time are astronomical. I replaced a couple IC's on the floppy analog board and it now functions. And I have desoldered the motherboard IWM and sockedted the placeholder.

Well what do I do for an IWM replacement (and some may be asking how do I know it was the IWM, well more on that in a bit)? These things are impossible to find. It occurred to me there are more likely many more battery bombed Apple IIgs boards than Apple IIc boards out there. I know from my experience that seems to be the case.

Lets rewind a bit and just over a year ago I had a Rom 03 apple IIgs with a bad IWM. @bladamson said he had a spare that might work but it came from a badly battery bombed board and was missing a bunch of legs. He sent it to me. The long and short is I never got to repair that rom 03 board as a marginal PSU I was using went rogue and blew out the board when it failed. So its delegated to parts now. I still had that IWM from @bladamson on my peg board.

Well I took out the dremel and a worn cutting wheel and started shaving away the ceramic to expose copper I could solder some resistor legs to so I can make the chip function again.

But what to do about the package difference? Both IC's are 28 pin but the IWM from the IIGS is PLCC. I searched around and found some plcc to dip adapters and even gerbers to make your own. Unfortunately I need to fix this sooner than later for the person who owns the IIc so time was of the essence. Alot of plcc to dip adapters are 28pin plcc to 24 pin dip which I dont really understand.. I need a 28 pin to 8 pin adapter so I bought this since it could arrive in 2 days: https://www.amazon.com/dp/B084QH35Q9?psc=1&ref=ppx_yo2ov_dt_b_product_details

Its made fairly well but it uses all SMD rather than through hole pin headers so Im suspect about its strength.. And its rather tall. Im sure most of you already assumed the floppy drive couldnt fit in the machine with a socket and this adapter sitting in it. And youd be right but lets cross that bridge later.

So here is the PLCC IWM which is still untested with a close shave and new legs:
IMG_20240630_151010.jpg

Here is the PLCC IC in the dip adapter. I checked continuity to every pin to make sure it was making a good connection and it is.



IMG_20240630_150836.jpg



So what happens when we flip the power and try loading up the IIe/IIc diagnostics? Well it boots up is what it does! The iigs plcc IWM is fully working!



IMG_20240630_151240.jpg



IT passes all the diags, it reads and writes, it boots up real floppy disks and my floppy emu just fine and seems to be completely working regardless of its Frankenstein appearance.

Ok lets address the elephant in the room. This will not work as is. I cant fit the floppy drive in the machine as the socket and adapter together are still about a quarter inch too tall. See these photos to show you what I mean:


IMG_20240630_153812.jpgIMG_20240630_153803.jpg

So what are my options? I could cut the pins shorter on the adapter. I think I can gain at least 1/16 of an inch at if I shorten them. Then I can remove the socket and just install the adapter directly onto the mainboard.... but I hate doing that.

Here is another idea. What if I install a an IDC to dip adapter? Here are some male idc dip connectors: https://www.ebay.com/itm/172138163630

I can have the idc dip connector in the new IWM socket on the mainboard, run a short 28 pin ribbon cable to a another IDC female dip 28 socket and place the adapter into it. Either under the floppy drive or behind it.. I will have to play around.
My biggest problem is I cannot seem to find the female 28 pin dip sockets I need. Can someone let me know where I can find those?


Would love to hear some input from the rest of you on this.

And lastly YES I KNOW I can use the DIP IWM from early compact macs. But I have repaired all of mine and I flat out refuse to sacrifice a working system/board for an IC. I keep dead boards just for occasions like this and what I have is a plcc IWM which I really believe are easily attainable from bad boards.

Anyway this whole thing is an experiment or proof of concept really since noone is currently working on a reverse engineered replacement yet as far as I know for this package chip and we have a need to fill.

I still have more work to do on this computer; I need to figure out the floppy mechanism situation and find a solution for fitting this iwm inside nicely.

Well let me know what you think and a big thanks again to @bladamson as this machine would still be unusable if it wasn't for his IWM.
 
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ETA: Disregard, this won't work since the PLCC socket is a SMT part (just noticed from looking at the Amazon listing). I'll preserve the original post below for amusement only:


Here's a bad idea, but I promise I'm not making it to be funny:

Can you remount the PLCC socket on the underside of the adaptor PCB and then push the PLCC "top first", "up" into the socket?

You may have to trim away some of the DIP socket on the IIc board for the modified adaptor to fit.

I don't know if this will work --- in particular, I don't know if the PLCC can make good contact this way --- but I think for it to have any hope of working, you'd need to be careful to flip the PLCC socket upside-down around this diagonal axis:

1719791184660.png
 
Thats really is a good idea.. but it being all smd negates that. I was pretty surprised its all smd. Seems this type of thing is always through hole.

The more I think about it, even soldering this adapter to the mainboard may still be too tall.
 
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Very nice work!

I have a ROM 01 IIGS with what I suspect to be a marginal IWM. It will boot software from a 5.25" without issue but trying to boot from known good 3.5" diskettes on a known good drive (both THOROUGHLY tested on a macintosh) always crashes at random places with $0027 (I/O error). When I first got the machine it would mostly work fine with 3.5" diskettes but would occasionally crash on cold boots from 3.5" with the I/O error. Now it has progressed to never being able to successfully complete a boot from 3.5" disk (using the exact same drive and diskette as previously). I should verify the clocking source to the IWM I suppose, but I doubt that's an issue since it still boots 5.25" properly and at least tries to boot from 3.5" and doesn't fail instantly. Since the IWM is attached directly to the floppy connector, I can't imagine it could be anything else.

Knowing that I could source a replacement IWM in either DIP or PLCC format will certainly help my quest for a replacement. But you say the PLCC ones are easily attainable? Perhaps I can find one...
 
So what are my options?
Is there something magic about this particular IIc?
The boards can't be so rare that you couldn't just replace the whole board for the cost of your time trying to bodge this one back to life.
Trying to buy anything from parts broker middlemen like ic2ic.com is also a waste of time, FWIW
 
Yeah I wasn't even considering a parts broker. Most just reply back with "parts not found". I have only had one instance where they were able to find me a couple IC's.

Its not my computer. But swapping a board just for an IWM is nuts. There are options as i have discovered. So sure this is a lesson in how to go about it but its also something new (which has piqued my interest) so I will find a way to make the plcc fit.

Swapping a board for one IC seems very novice if there are alternatives.. And there are still a few.

As far as my time is concerned. I get it. Most wouldn't go to this length, but I am in no means a time crunch. Im doing it at my leisure. And since this is the first IIC IWM to ever fail on any I have worked on I am curious of how to handle it in the future.

At the end of the day most people would think any amount of effort on these old machines is pointless. I guess we decide how much effort is worth it on an individual basis.
 
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Trying to buy anything from parts broker middlemen like ic2ic.com is also a waste of time, FWIW

Possibly, your milage may vary as they say.

Some years back now, the clock chip in my IIgs failed.

I was able to source a compatible replacement through a broker. (3440042B is from a MacPlus, but works just fine).

Had to buy a tube of 20 though :rolleyes:

RTC_replacement.png

Regards,
Red
 
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