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Need help: 1200XL no SIO (Won't read disk or SIO2SD)


56 replies to this topic

#51 DrVenkman ONLINE  

DrVenkman

    River Patroller

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Posted Tue Mar 20, 2018 5:51 AM

Huh?
+5 READY line is not used for power if that is what
is behind the thinking there, it's only purpose
is to tell devices on the SIO chain that the computer
has power and is READY.

My real drive with R63 intact would not work, so I
jumped it and then it did work. Only thing I did too.

Are you sure you didn’t have something else going on? Why the heck would Atari release a computer their own disk drives wouldn’t work with?

Besides, R63 is a current LIMITING resistor. It doesn’t disconnect the signal entirely.

#52 1050 OFFLINE  

1050

    Dragonstomper

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Posted Tue Mar 20, 2018 10:03 AM

Pretty sure. I had three drives and they all failed
to boot my new to me 1200XL I got from the guy who
single handedly shut down comp.sys.8bit for $25 IIRC.
This was a good while before he became a relentless
pest over there.

Digging thru that group I came across R63 advice and
tried it having nothing else. And it started working
with all three drives perfect.

They worked when new, but age has it's effects, I
suspect it's the aging of the 3086 and the loss of
gain there that makes R63 issues pop up after all
this time. New, it was working fine and would easily
pass all testing.

I've done the math, it's unbelievable and opposite
to my position too. Which is why I don't lead with it.
100 ohms should not have any effect on 0.34 ma that the
1050 draws from +5 READY line for a bias voltage of
1.67 on the base of a 3086 transistor. But it does
have a profound effect. The edge must be a very fine
one is all I have. And the advice to try it - because
it worked for me and unknown numbers of others with the
same advice after theirs start working again too. I agree
with you, it shouldn't matter. But somehow it's a problem,
and I just don't have a decent answer as to why.

#53 Calibus OFFLINE  

Calibus

    Space Invader

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Posted Tue Mar 20, 2018 10:14 AM

I'll probably try the R63 mod, at this point, I don't have anything to lose.

Unfortunately, due to busy evenings, probably will not be able to try it for a day or so.



#54 flashjazzcat ONLINE  

flashjazzcat

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Posted Tue Mar 20, 2018 10:35 AM

Not sure if anyone asked this yet, but does SIO work if you remove U1MB and fit an XE MMU and OS ROM?

#55 Calibus OFFLINE  

Calibus

    Space Invader

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Posted Tue Mar 20, 2018 11:07 AM

Not sure if anyone asked this yet, but does SIO work if you remove U1MB and fit an XE MMU and OS ROM?

 

If this is directed to me, I'm not sure what you are referring to as an XE MMU.  I still have the XL MMU I removed the 1200XL prior to installing the U1MB and the two ROMs.

I purposely haven't reverted the 1200XL back to stock configuration due to the jumpers I moved around to modify the ROM addressing.

While I am comfortable soldering, I'm leery of doing more than necessary since there is always the slight chance of causing a problem and I'd hate to make matters worse.

 

Believe me, I am kicking myself for neglecting to test the SIO port prior to performing any mods - I had never used the SIO port until recently, so it wasn't like a habit to even think about it....

 

When my 800XL arrives, I am definitely planning on giving it a thorough checkout before cracking the case...

And only AFTER I have verified the SIO works - opening it up and scoping the TX pin to see how it compares to the 1200XL.



#56 flashjazzcat ONLINE  

flashjazzcat

    Quadrunner

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Posted Tue Mar 20, 2018 11:24 AM

Yes: it's for your attention and a direct response to the previous post. :) I should have perhaps written XL/XE MMU, but that's part number CO61618 and quite different to the 1200XL MMU you removed when installing U1MB. Not sure if the 1200XL MMU would still allow basic functionality with a single chip OS ROM, but you could try it. I doubt U1MB is to blame in any way, but removing it would at least eliminate any issues with the ribbon cabling or the modifications you made to the IDC headers.

#57 Calibus OFFLINE  

Calibus

    Space Invader

  • 43 posts
  • Location:Akron Ohio

Posted Thu Mar 22, 2018 7:13 PM

OK,

go ahead and line up and tell me "I told you so"

 

I swapped out R63 for one of the jumpers I removed when I installed my U1MB, and the SIO is now working perfectly with the Atarimax SIO2PC-USB device.

 

*sigh*

All's well that ends well I guess

 

Jim






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