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Resistors on SIO port


lbaeza
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Hi

 

I am helping a friend to troubleshoot his 130XE computer remotely, I don't have physical access to his computer.

The computer has several issues, broken keyboard membrane and possibly a bad Antic.

But one thing is a mistery to me with this computer: it has several resistors soldered right at the SIO port.

Please see attached picture.

Any ideas what is the purpose of these resistors on the SIO port?

Kind regards,

 

Louis BQ

 

PS: The original thread in spanish can be found here: http://www.atariware.cl/aw/foro/viewtopic.php?f=13&t=3022

post-86-0-73027900-1512439901_thumb.jpg

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for the millionth explanation they are capacitors... and should cut off the ones to read, write, and command...

 

that the 3rd 4th and fifth I think from the right side going left on your picture as it is orientated..

 

google and forum search is your friend....

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I would cut them all off, because none of them are required for SIO to communicate properly. In fact in reference to the pins already mentioned, having the capacitors can actually hamper high-speed coms. The original purpose was to improve the ESD protection to the I/O pins of the Pokey and PIA (6520) chips. However I've yet to zap a chip without these capacitors in place.

 

- Michael

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that's not entirely correct, they were to help with two things esd and the fcc for radio interference... a bs pain in the ass had to be done to make happy government...

 

Yes that is true, but now days the emissions aspect would be very low on the list of concerns especially at the relatively low frequencies in play. I think the ESD aspect is the much more important of the two (I'm thinking young kids playing their Atari's on the living room TV with the unit resting on the old 70's era shag carpeting - lot's of static potential).

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Hi to all !! I’m the owner of that capacitors nest. The thing is that my 1050 doesn’t communicate properly and works bad. Lots of Boot Errors, bad reading and I can’t write any disk. When I use it for a while, errors from my 1050 increases. When I turn it on, it start reading all the disks and then none.

As you told, I understand that it was made because of radio interferences, but I can’t understand how it worked at the begining and not now? Or it never worked?

 

My doubt is if it was made because some problem, to make some kind of bridge or to improve performance..lol..?

 

As I read, I can conclude that I should take them all off? Please tell me what to do? Thanks a lot !!!

 

Gulff

P.D. The Video of my old 1982 computer broke due to a video cable I bought to connect it to a led tv. Because of that, I bought another used 130 xe computer, in order to fix it. I repair my old computer, but the one I bought have this transistors on the SIO Port.

Edited by Gulff
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The original purpose was to improve the ESD protection to the I/O pins of the Pokey and PIA (6520) chips. However I've yet to zap a chip without these capacitors in place.

 

I haven't either, but one of my machines (a 1200XL) came into my hands with a zapped POKEY, and I've had two 2600's with partially-bad 6532 RIOT chips. The shag carpet-induced static struggle was real, yo. :P

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I guess we're full of static over here :)

 

Judging by the hair of your president I'm pretty sure ! :D :D :D

 

Definitly never saw this on a PAL 130XE....anyone else in Europe ?

 

I have a feeling homes might have more carpet flooring in the US ? Most houses here have wood, tile, laminate etc. type of flooring....although that was a bit different in the 70's I guess this came up in the 80's so....who knows... it could be, right ?

 

Whatever the reason it is one hell of a hideous factory mod !

Edited by Level42
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Back to the topic.

The capacitors are there to make sure the computer complies with FCC rules.

For static, they don't do much.

They will limit the communication speed as it takes time to charge and discharge them.

If you use correct and shielded cables and make sure the connected devices are shielded. It's no real problem to remove them.

And in reality, you won't get into any truoble if you remove them.

 

BR/

Guus

Edited by guus.assmann
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Back to the topic.

The capacitors are there to make sure the computer complies with FCC rules.

 

 

...which would confirm that it is US only.....

 

So they are there to reduce noise getting OUT of the XE instead of protecting it from getting in....

 

And I agree that caps do little against static. You'd at least need some zenerdiodes....

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Later revisions of the 130XE boards had them cleaned up and built into the board, starting with REV 5 and REV B. It is still debatable when/if they get populated on R 5 and B board.

 

Rev 5 w/o but locations for: them http://ataricomputers.altervista.org/130XE/130XE_561035759_MOBO_FRONT.jpg

 

Rev B populated: post-46210-0-34815100-1466854554.jpg

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  • 5 months later...

Are those capacitors on 400s and 800s, too? I need to open my 400 because a screw fell off the lid hinge and that would be a good opportunity to cut them off if that is required.

Edited by slx
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Are those capacitors on 400s and 800s, too? I need to open my 400 because a screw fell off the lid hinge and that would be a good opportunity to cut them off if that is required.

 

Nope. Nor on (most?) XL's. None of my machines have them except my 130XE.

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