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External 400k Floppy / Original Mac Keyboard Issues

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raoulduke

Experienced Member
Joined
Jan 14, 2015
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356
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The keyboard doesn't seem to work at all, but my Mac Plus keyboard works fine on the Macintosh. The TI SN74LS123N chip's pins seem blackened, so my I'm going to replace that next - I've cleaned the traces on the bottom with isopropyl and reseated that chip and the Intel 8021 chip to no effect. *I forgot to mention that I also resoldered the four pins on the interface, also to no effect.

I cleaned the external floppy and mostly unstuck it. When I turn it on it can adjust the head distance properly (i.e. when I push it toward the back, the screw will turn and pull it in). Then it seems to flip the plastic the head is on up repeatedly while a red light is on and it makes a repetitive sound I'm failing to describe. Is this a symptom of something just being stuck? Putting a disk in doesn't help.
 
Still waiting on the chip for the keyboard but the floppy has an even more bizarre issue. It recognizes inserted floppies and is capable of formatting and reading; but it is not cross-readable with the internal floppy: I can read/write with the internal and external floppies, but cannot then use the alternate drive to read that disk. I figure there's some sort of non-fatal misalignment but I don't know enough and am not sure how to attack the problem further; any thoughts? [I guess worst case scenario I can still use it as a backup drive.]
 
Okay, I may have missed something, but how many drives are we using here? Is it one external 400k, and one internal 400k, or is there a third drive here as well? Is this a 128k/512k and a 400k internal drive, or a 512k and an 800k internal drive? Are there any SuperDrives involved at all here? Because Mac floppy issues can be notoriously complicated, and you need to list out all the info you have to figure out if you're dealing with something broken, or with something just not being compatible.

It should be readable on any drive, but bear in mind that 400k drives/Macs use MFS to read/write, and 800k and above use HFS. Unless you're working with 7.6.1, there won't be any issue of writing to an MFS volume, however.

Keep in mind that the drive uses a varying speed mechanism for read/write regardless, and I'd surmise that could be a common issue that pops up, besides misalignment.
 
Sorry it's just two - the internal and external 400k drives on a Mac - although a Mac upgraded to 512k (though only the motherboard and not the drive, AFAIK - the manual listed several possible upgrade packages - of this fact I had not previously been aware).

I have most of the original disks, including all the system disks. They work fine on the internal but will not read on the external. This, to me, indicates that the read/write issue is confined to the external drive.

Likewise, disks formatted on the external read fine on the external drive but do not read at all on the internal drive.
 
Most likely, track alignment is messed up on the external drive.

http://www.willegal.net/blog/?p=6218

regards,
Mike Willegal


raoulduke said:
Sorry it's just two - the internal and external 400k drives on a Mac - although a Mac upgraded to 512k (though only the motherboard and not the drive, AFAIK - the manual listed several possible upgrade packages - of this fact I had not previously been aware).

I have most of the original disks, including all the system disks. They work fine on the internal but will not read on the external. This, to me, indicates that the read/write issue is confined to the external drive.

Likewise, disks formatted on the external read fine on the external drive but do not read at all on the internal drive.
Click to expand...
 
Looks like it. Thanks.

Oh okay... Yeah I screwed with the tweaking screw; although it was still misaligned before I screwed with it.
 
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Well that wasn't the least tedious thing I've ever done but it worked.

tmp_19722-20161011_213808-1497415719.jpg

One more issue (at least until the keyboard microchip gets here). The screen randomly flickers off. When I tap the back case it flickers back on. I pressed on the "CRT socket video cable" (the thing that fits on the back of the CRT neck) but it's firmly on there and that's not the issue. [http://www.ccadams.org/se/screen.html Re: Twitching screen] maybe it's the connector? That'd potentially explain why screwing with the yoke had some effect.
 
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The screen randomly flickers off.
Click to expand...

Probably your issue is due to bad solders.

Same problem in mostly all Macintosh 128/512/Plus and SE units.

Removing old solder from Yoke connector Y1 and soldering back fresh one is the first step, do the same thing with the soldering points of the Flyback transformer and logic board to Analog board cable connector J4.
 
Taking out and replacing the (same) cable seems to have worked for the moment. I'll touch up the solder points if (more likely when) it starts again.

I have to redo the disk alignment because putting the drive (chassis) in the case screwed with it (lol - very annoying process; screwing the screw itself slightly throws off the alignment of it not being screwed in - making the diagnostic process insane).

I got the replacement TI chip for the keyboard and replacing it (probably not surprisingly) didn't work. I get no response at all from the keyboard. Pina classifies this as a "dead keyboard" and says to replace the logic IC (http://maccaps.com/MacCaps/Repair_books_files/Macintosh Repair and Upgrade Secrets.pdf - pg. 217-18 ), which in the 128k's case is an Intel 8021H chip.

Alibaba may sell this (https://www.alibaba.com/product-det..._1957070554.html?spm=a2700.7724838.0.0.UPWNlA) [P8021H2173] but does anyone have better ideas of where to find one?
 
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raoulduke said:
Taking out and replacing the (same) cable seems to have worked for the moment. I'll touch up the solder points if (more likely when) it starts again.

I have to redo the disk alignment because putting the drive (chassis) in the case screwed with it (lol - very annoying process; screwing the screw itself slightly throws off the alignment of it not being screwed in - making the diagnostic process insane).

I got the replacement TI chip for the keyboard and replacing it (probably not surprisingly) didn't work. I get no response at all from the keyboard. Pina classifies this as a "dead keyboard" and says to replace the logic IC (http://maccaps.com/MacCaps/Repair_books_files/Macintosh Repair and Upgrade Secrets.pdf - pg. 217-18 ), which in the 128k's case is an Intel 8021H chip.

Alibaba may sell this (https://www.alibaba.com/product-det..._1957070554.html?spm=a2700.7724838.0.0.UPWNlA) [P8021H2173] but does anyone have better ideas of where to find one?
Click to expand...

Be aware that EMI from the CRT circuit will prevent the internal floppy from working unless the metal sheild is in place.

regards,
Mike Willegal
 
Thanks. I'm not messing with the internal floppy at the moment, though, and the shield is in place.

On the 8021H; there are multiple suffix codes - what do they mean - as in what does 2173 (in P8021H 2173) mean?
 
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raoulduke said:
Thanks. I'm not messing with the internal floppy at the moment, though, and the shield is in place.

On the 8021H; there are multiple suffix codes - what do they mean - as in what does 2173 (in P8021H 2173) mean?
Click to expand...

Probably a date code. Normally, they're seen in the form of YYWW, where YY is the last two digits of the year, and WW is the week of the year it was produced. As for that code, though, I'm not sure of its format. In any case, all you need to be sure of is that the main number of the new chip is similar to that of the old one. Good luck!
-Adam
 
That's what I thought originally, but it may be the ROM mask number. Thanks; luck is something I will definitely need.
 
Hers a site I found with info on Intel IC codes:

http://www.antiquetech.com/?page_id=809

According to that page, Intel used the standard YYWW date code system on their chips. If the chip you're referring to isn't made by Intel, you might be able to find the info you need elsewhere on that site. Again, good luck!
-Adam
 
Thanks for those; sorry I thought I thanked you a while ago.

I finally fixed the drive permanently last night and I wanted to note that the rear optical switch issue - the click of death - wasn't because the switch was dirty; it's that when the board under the alignment screw is pushed all the way back it doesn't limit whatever that head screw is called and that actually causes the click of death. The solution is to push the board forward, which, not ironically, is also the fix for getting it to read and write disks properly after solving the click of death.
 
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