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

[+DrVenkman]

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.

[1050]

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.

[Calibus]

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.

[flashjazzcat]

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

[Calibus]

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.

[flashjazzcat]

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.

[Calibus]

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