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Apple IIGS Floppy Drive Weirdness

The only way I see to proceed on this since you apparently have another //gs and 5.25 drive is with a scope to do side by side comparison of identical functions walking around the pins of the IWM but is it worth it?
The concern would be one slip of a scope probe on the good machine could be disastrous. And even if you determine the chip is bad, is it even available or replaceable? I used to change postage stamp IC's with
a butane pen to heat the old chip leads and lift it. Chips were sometimes also glued down so I had to heat the body enough to melt it. It pretty much destroys the old chip. There were square tips for irons to do the
desoldering but they were expensive and custom sized plus if glued, just couldn't heat enough to melt. The butane pen worked well with just a continuous circling of the chip. That's my experience, anyway ...

Larry G
 
>Here's a interesting new wrinkle. I tried attaching a 3 1/2" drive, the Apple 3.5 Drive (A9M0106), and booting GS/OS 6.0 off of a 3 1/2" disk. It booted fine! I then daisy chained a 5 1/4" drive off of it. With >nothing in the 5 1/4" drive I booted it up. The 5 1/4" drive was accessed, the drive clicks and the light goes on. It boots fine off of the 3 1/2" disk. But there's no 5 1/4" drive on the desktop! Huh?

There is a different part# of 5.25 drive listed for the //gs and you have the correct ones. I'm guessing those //gs drives have special lines to detect presence for the smartport.
Looking again at the //gs schematic, there are select lines running to the floppy connector from the VGC chip !! The VGC might be socketed if you want to try a swap ...

Larry G
 
Larry -

I don't have a scope, yet, but it's something to try when I get one.

I was looking at the IWM and it doesn't look easy to replace. I can't find anywhere to buy a replacement, so that fact that I can't replace it may not matter! :)

Swapping the VGC is certainly possible - it is socketed. I'll give that a try.

- Rick
 
I vaguely recall reading something about defective VGC chip revisions, too—they could be discerned by certain ranges of the numbers stamped on the top. Did the defect affect floppy control? No idea, but possibly worth looking up.
 
gsteemso said:
I vaguely recall reading something about defective VGC chip revisions, too—they could be discerned by certain ranges of the numbers stamped on the top. Did the defect affect floppy control? No idea, but possibly worth looking up.
Click to expand...

Unless someone did something dodgy, if it's a ROM 01 system, it should have the fixed VGC as well as the ROM 01 PROM. Apple shipped them as a kit together...

The VGC problem had to do with pink fringes around DHGR monochrome graphics, if I recall correctly. Not an issue with the floppy controller I/O.
 
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