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XF551 Schematics


kheller2

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Just to keep things lively, this is the set of all (known to me) XF schematics. Maybe this way I can find them easier the next time I look for them. ;-)

 

Mariusz Geisler

post-4566-0-20751100-1540511726_thumb.gif

 

From: http://blog.3b2.sk/igi/post/Chyby-v-scheme-ATARI-XF-551-Bugs-in-circuit-ATARI-XF551.aspx

Igor Gramblicka V1

post-4566-0-61049800-1540511719_thumb.gif

 

Igor Gramblicka V2

post-4566-0-29679600-1540511712_thumb.gif

 

 

From: https://atariwiki.org/wiki/Wiki.jsp?page=Atari%20XF551

Atari Japan Preliminary

XF551_schematic.pdf

 

 

 

And from the FAQ:

The reverse side of a 2-sided "flippy" disk may be used by inserting the disk into the drive upside-down.

But note:

Chinon-built XF551--CANNOT read/write/format disk backside if the disk has no 2nd timing hole
Mitsumi-built XF551--CAN read/write disk backside if the disk has no 2nd timing hole, but CANNOT format the backside without the 2nd timing hole.
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Nice. I never realized the simplicity of the XF551 PCB design compared to the 1050.....really makes building a drive "from scratch" possible.

 

Since the drive uses a "standard industry (shugar?) FDD connection, would it be possible to hook up a Gotek ? not that it would be the most logical option for our A8 (f.i. Sdrive Max is a more logical and economical solution) but it would be fun if it would be possible.

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The full wave rectifier is a 7 volt rectifier not a

12 volt rectifier.

C102 is not in series to the DC side of the full wave rectifier,

it is in series to one AC side of the full wave rectifier

which is how a voltage doubler circuit works. 1050 drive

also has this circuit.

 

D2 conducts during one half of AC cycle and D3 conducts

during the other half of AC cycle. Together with help from

C103 to establish 7 volt positive to push from, they pump

the voltage up to 21 volts during D3 conduction half

cycle at C104 which holds the very choppy 21 volt

charge for the 12 volt regulator to work with.

 

Suffice to say it works? You can boggle your mind as

to exactly how on your time as I may not have explained

it in a manner you need to hear in order to make any

real sense for you. Teaching is a talent and I may

posses little if any. I'm also firmly entrenched in

electron flow theory rather than conventional current

theory - I maybe just confusing you then.

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Nice. I never realized the simplicity of the XF551 PCB design compared to the 1050.....really makes building a drive "from scratch" possible.

 

Since the drive uses a "standard industry (shugar?) FDD connection, would it be possible to hook up a Gotek ? not that it would be the most logical option for our A8 (f.i. Sdrive Max is a more logical and economical solution) but it would be fun if it would be possible.

 

 

Yes, its eerily similar to the unreleased 1053 that used a 8039/8049 and 2797: http://www.atarimuseum.com/computers/8BITS/XL/xlperipherals/1053/1053-diskcontroller-schem.gif

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This all makes so much sense now.

 

When the XF551 was released I was totally amazed. I hadnt expected Atari Corp to still make such a big effort for the 8 bit series....it was SO late...the XEGS was already there....

 

Basically, from what I googled, it seems safe enough to sum it up like this:

 

- Corp. never had interest to release a new FDD for the A8, they happily advertised the 130XE with a 1050 next to it....

- Corp. was sued by Nintendo because commercials claimed the XEGS to be possible to turn in a real computer yet there was no FDD for it.

- Corp. panicked, jumped into the technical archives, dug out an old design, adapted it to use the WD1772 they used for the ST series and bam...there was the XF551, with a possible idea for going 3.5 FDD considered briefly...

- Corp. launched the XF551 with DOS 2.5, hiding the true power of the drive, but they needed to hurry because of Nintendo...

- Corp. found an old DOS 2.5 document, replaced 1050 with XF551 and published as the XF551 DOS 2.5 manual.....the specs page even lists a 6507 and all the other 1050 specs for the XF551, bunch of liars ;)

Edited by Level42
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Hello guys

 

Years ago, Atari Benelux released a lot of their schematics to the SAG. We probably have Guus Assmann to thank for this, as he was the president of the SAG and at one point in time was an employee of Atari Benelux. Among the schematics release where the schematics of the XF551. As soon as I found out how to properly scan the schematics, I'll upload them here. Tips are welcome.

 

Sincerely

 

Mathy

 

PS members of the ABBUC will probably find the schematics (of not only the XF551) on the ABBUC website.

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This all makes so much sense now.

 

When the XF551 was released I was totally amazed. I hadnt expected Atari Corp to still make such a big effort for the 8 bit series....it was SO late...the XEGS was already there....

 

Basically, from what I googled, it seems safe enough to sum it up like this:

 

- Corp. never had interest to release a new FDD for the A8, they happily advertised the 130XE with a 1050 next to it....

- Corp. was sued by Nintendo because commercials claimed the XEGS to be possible to turn in a real computer yet there was no FDD for it.

- Corp. panicked, jumped into the technical archives, dug out an old design, adapted it to use the WD1772 they used for the ST series and bam...there was the XF551, with a possible idea for going 3.5 FDD considered briefly...

- Corp. launched the XF551 with DOS 2.5, hiding the true power of the drive, but they needed to hurry because of Nintendo...

- Corp. found an old DOS 2.5 document, replaced 1050 with XF551 and published as the XF551 DOS 2.5 manual.....the specs page even lists a 6507 and all the other 1050 specs for the XF551, bunch of liars ;)

 

That's got to be one of the strangest lawsuits ever, and I suspect there is more to it than what has been stated.

 

Whether or not a FDD was available doesn't negate the fact that it was indeed a real computer. If you can enter a program via a keyboard and run that program, it's a computer. Saving to and/or loading from floppies is a plus, not a necessity in order to be called a computer. On top of that, it did come with the standard SIO port same as all the other 8-bit Atari computers. So you could still use any of the peripheral storage, modem, and printing devices that Atari (and others) had previously made for the computer line.

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Hello guys

 

Years ago, Atari Benelux released a lot of their schematics to the SAG. We probably have Guus Assmann to thank for this, as he was the president of the SAG and at one point in time was an employee of Atari Benelux. Among the schematics release where the schematics of the XF551. As soon as I found out how to properly scan the schematics, I'll upload them here. Tips are welcome.

 

Sincerely

 

Mathy

 

PS members of the ABBUC will probably find the schematics (of not only the XF551) on the ABBUC website.

Is there a list of all the materials that were released?

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Hello guys

 

Years ago, Atari Benelux released a lot of their schematics to the SAG. We probably have Guus Assmann to thank for this, as he was the president of the SAG and at one point in time was an employee of Atari Benelux. Among the schematics release where the schematics of the XF551. As soon as I found out how to properly scan the schematics, I'll upload them here. Tips are welcome.

 

Sincerely

 

Mathy

 

PS members of the ABBUC will probably find the schematics (of not only the XF551) on the ABBUC website.

When was Guus president of SAG ? “In my time” it was Casper Jansen.....

 

I received this set of schematics from Atari Benelux because I was secretary of SAG Regio Rijnmond for a while....and did the technical support stuff... still have them, mostly ST though....if not only ST.....they are printed on red paper to prevent copying them on photocopier machines....LOL.

 

Don’t think the XF551 is in that set as I received the set before the XF was released....

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Hello Andre

 

Not sure when. But Guus probably knows. :grin:

 

I have a set including the 600XL, 800XL, 130XE, 1010, 1020, 1027, 1029, 1050, 850 and 1064. And a similar envelope of the SAG with the schematics of the XF551.

 

Sincerely

 

Mathy

Is there a club reason these haven’t been published?

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Hello kheller2

 

SAG seized to exist when internet wasn't available to the public yet. And I guess nobody's had the idea to publish them on the net. Except IIRC ABBUC, but you have to be a member to be able to download them. ABBUC is some cases also the complete SAMs manuals.

 

Sincerely

 

Mathy

 

 

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  • 1 year later...
  • 3 years later...

I think I'll give this thread a bump and ask a couple of questions while I'm at it.

 

So I was looking at the schematics for the XF551 both the ones posted here and also one that had been drawn by Mariusz Geisler back in 1993 and was very curious about a couple of things that Atari had done (particularly the areas I circled in red).

 

XF551_Schema_SnapShot.thumb.png.2b76d89d9434179c257da80afbc27b15.png

 

So first up would be the pull-up resistor R8 (3.3K). I'm assuming since U3A was feeding into a Schmitt Trigger Inverter (74LS14), they wanted to modify the normal hysteresis to have a faster transition making it akin to using a 74LS04 instead. Because to my knowledge using a pull-up resistor on the output of an LS device was usually only called for when driving into a CMOS gate which requires a higher voltage than LS normally outputs for a high.

 

Moving on...

 

But what totally baffles me is the reason for the 3.3V zener regulated power supply feeding only one input of U3D which is a NAND gate inverting the Write Gate output of the WD1772 prior to connection to the floppy drive. Why the lower voltage on that pin?

 

-------------

 

EDIT: Just found the answer to my first question about the pull-up resistor. The 74LS38 has an open collector output, so the pull-up resistor gives it an actual high state which it normally wouldn't have.

 

EDIT2: Since I wasn't having much luck looking for the answer to my 2nd inquiry via Google, I decided to try their ChatGPT experiment BARD instead and here's what came back as a response...

Quote

There are a few reasons why one input of a 74LS 2-input NAND gate might be tied to a voltage between GND and VCC.

  • To create a logical constant. If one input is tied to a high voltage, the NAND gate will always output a low voltage. This can be used to create a logical constant, such as a 1 or a 0.
  • To create a wired-AND function. If two NAND gates are connected with their outputs tied together, and one input of each gate is tied to a high voltage, the output of the combined circuit will be a logical 1 only when both inputs of the first gate are 0. This is the same as the wired-AND function.
  • To create a level shifter. If one input of a NAND gate is tied to a voltage that is different from the supply voltage, the output of the gate will be at a different voltage level. This can be used to shift the voltage level of a signal from one level to another.

I think the 3rd possibility of it being a level shifter seems the most plausible. And that surprised me, since I never knew something like that would even be possible with a standard 74LS part.

 

Mariusz Geisler Full Schematic

Spoiler

XF551_schema.thumb.gif.113b761b772eef23967533cdce5f2964.gif

 

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2 minutes ago, kheller2 said:

Why would you need 3.3 shifted on the WG signal to the floppy mech write enable?

I've been thinking the same thing. And the level shifting aspect wouldn't work for the 74LS38 which is open collector and hence has no HIGH level of it's own anyway, thus relying on the 'normal' high state of the Write-Gate signal line on the floppy drive.

 

So I'm once more baffled by what this circuit is truly suppose to do ???

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8 minutes ago, kheller2 said:

Perhaps a holdover from the failed XF351 3.5" that used ST drives?

Did the ST drives use a lower 3.3V interface?

 

But for that circuit to level shift it would need to be a standard TTL output NAND gate if Bard's response were correct. And with the 74LS38 being open collector, no level shifting would seem to be necessary anyway since Write-Gate is a active low signal.

 

I think I have a partially disassembled XF around my shop somewhere. Perhaps that'll be my project for today to get it up and working, and then see what that circuit is truly doing or even if it's necessary.

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