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1200XL M.U.L.E.

1200XL SIO Fix (R63) and ROM select line mod

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I attempted two modifications to my spare 1200XL motherboard and wanted to share my results in case anyone would be interested in seeing.

 

First, I wanted to replace the 100 Ohm resistor in position R63 with a 0 Ohm resistor. This is the "SIO fix" and should allow SIO devices to draw +5V power from the SIO port. I was expecting to see a carbon based resistor with brown, black, and brown color bands. Instead, I saw this.

 

r63.thumb.jpg.0a64816b04a60d560e3ba814d9760957.jpg

 

I'm not sure what that is. Although it's not completely proper, I measured the resistance across that device and my meter registered 0 Ohms. Could this motherboard already have the SIO fix installed?

 

I also de-soldered the three 0 Ohm ROM select resistors. Assuming I didn't goof up here, these are in positions W9, W8, and W7. I replaced them with SIP sockets and inserted new 0 Ohm resistors into the sockets. The completed work looks like this.

 

1290246493_0ohm.thumb.jpg.1a9c39cef08ad28c5697aed3fbc12d45.jpg

 

The goal was to give myself future flexibility in my ROM selection. I can insert 0 Ohm resistors in whatever position I need to accommodate whatever ROM I would like. Additionally, if I need to draw these points out somewhere then I have a non-permanent insertion point to tap into. I am no longer soldering and de-soldering which could heat stress the motherboard.

 

I thought I would be clever and mark the width of the SIP sockets onto the resistor legs. That would have given me point to bend the resistor leg. It wasn't such a good idea. I used a red Sharpie pen and ended up coloring my fingers and the sockets. :( It was easier to simply eye ball the width, bend the leg, and insert. Just goes to show ... you're not always as clever as you think you are. ;) 

 

I wanted to go further with two more mods but ran out of time. First, I wanted to add two SIP sockets to the current ROM sockets. This would extend the 24 pin socket to 28 pins and maybe negate the need for replacing the socket. My SIP socket is 40 pins long and I broke off 2 pins. UNfortunately, none of the breaks are perfect-perfect. There's a bit of plastic material that prevents the SIP socket from going straight down. The 2 pin socket is a little cocked due to the extra material on the side from the break. I decided installing this would have been sloppy so I didn't do it. Instead, I will install honest to goodness 28 pin sockets. Second, I wanted to remove the RF modulator but I saw just how hefty those solder joints are. I need to think about how I'm going to heat that solder and wick and suck it away. Its all too easy to stick and hold a soldering iron in place and overcook the board.  I welcome recommendations on how to do this well.

 

Thanks!

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Posted (edited)

looks like an inductor or choke to me, if is were a zero ohm and bead affair (jumper with toroid cylinder, the cylinder is normally loose.)

You can measure it, If it's zero - great. I things seem slow to come up to speed or it gets warm then it's choking the line.. at that point it's a thing to replace.

Edited by _The Doctor__
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8 hours ago, 1200XL M.U.L.E. said:

Second, I wanted to remove the RF modulator but I saw just how hefty those solder joints are. I need to think about how I'm going to heat that solder and wick and suck it away. Its all too easy to stick and hold a soldering iron in place and overcook the board.  I welcome recommendations on how to do this well.

I remove RF cans the way I’ve seen Flashjazzcat do it - first clip the signal wires going into thr modulator. Next, put the biggest tip you have on your iron and start heating up the pad or pads closest to the edge of the board. Don’t worry about cooking the board - the modulators have a huge thermal mass and will take a relatively long time to heat up to even let solder melt at all, let alone damage the board. Once the pad or pads nearest the edge get get melty, slide a thin flat blade jeweler’s screwdriver under the edge of the can and start to lift gently, hearing the pads as you do. You won’t need much force once things are good and melted. After a few minutes the board will start lifting off of the board.  Repeat for the additional pads, taking care not to use too much force. After a few minutes the can will come free. Then you can clean out the pads and the signal wires at your leisure.

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@1200XL M.U.L.E. I love that idea of putting those SIP sockets/header strips in place of the jumpers. I should have done this on 1050's when modding to use EPROM instead of mask ROM. And remove risk of damage from repeated re-configurations. For the next one!

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11 hours ago, 1200XL M.U.L.E. said:

The goal was to give myself future flexibility in my ROM selection. I can insert 0 Ohm resistors in whatever position I need to accommodate whatever ROM I would like. Additionally, if I need to draw these points out somewhere then I have a non-permanent insertion point to tap into. I am no longer soldering and de-soldering which could heat stress the motherboard.

SOLID thinking, right here!

 

Glad you resisted the (worthless) notion that it is ok. to internally turn your machine into a spa-ghetto of cables and soldering-kludge (like a lot of crap I see floating around).

 

I will re-cycle your concept on my end for cleaner, less-intrusive and flexible mods.

 

I wonder if these SIP sockets can be cut / ordered to a single-pin, two-pin or any arbitrary pin-# length?

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Posted (edited)
50 minutes ago, Nezgar said:

@1200XL M.U.L.E. I love that idea of putting those SIP sockets/header strips in place of the jumpers. I should have done this on 1050's when modding to use EPROM instead of mask ROM. And remove risk of damage from repeated re-configurations. For the next one!

Me too.

 

As for the SIP on the 24-pin rom sockets, that is what I did as well instead of desoldering the originals and taking the chance of lifting pads or traces and heat damage. I just wish I'd thought of doing it to the jumpers as well!

Edited by Gunstar
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49 minutes ago, Faicuai said:

I wonder if these SIP sockets can be cut / ordered to a single-pin, two-pin or any arbitrary pin-# length?

Yes, they come in strips of 40 pins, and you can break/cut them to any length you want, including 1.

 

For example: https://www.ebay.com/itm/381374700001

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Posted (edited)
4 hours ago, _The Doctor__ said:

looks like an inductor or choke to me, if is were a zero ohm and bead affair (jumper with toroid cylinder, the cylinder is normally loose.)

You can measure it, If it's zero - great. I things seem slow to come up to speed or it gets warm then it's choking the line.. at that point it's a thing to replace.

 

@_The Doctor__ Ahh, I didn't think that it could be choke or inductor. That would explain the 0 Ohm measurement at DC with the meter. I wonder how many other 1200XL motherboards have a choke or inductor here instead of a resistor. I think I will leave this component alone for now.

 

4 hours ago, DrVenkman said:

I remove RF cans the way I’ve seen Flashjazzcat do it - first clip the signal wires going into thr modulator. Next, put the biggest tip you have on your iron and start heating up the pad or pads closest to the edge of the board. Don’t worry about cooking the board - the modulators have a huge thermal mass and will take a relatively long time to heat up to even let solder melt at all, let alone damage the board. Once the pad or pads nearest the edge get get melty, slide a thin flat blade jeweler’s screwdriver under the edge of the can and start to lift gently, hearing the pads as you do. You won’t need much force once things are good and melted. After a few minutes the board will start lifting off of the board.  Repeat for the additional pads, taking care not to use too much force. After a few minutes the can will come free. Then you can clean out the pads and the signal wires at your leisure.

 

@DrVenkman Ohh! You clip those through-hole leads from the RF modulator? That's a little too destructive for me, even if I never plan to use the RF modulator ever again. The mass of the modulator scared me a little bit. I would need to heat soak the connection due to the mass absorbing so much heat. That would heat up the board in parallel. Maybe I can try removing one connection and see how it all goes.

 

1 hour ago, Faicuai said:

SOLID thinking, right here!

 

Glad you resisted the (worthless) notion that it is ok. to internally turn your machine into a spa-ghetto of cables and soldering-kludge (like a lot of crap I see floating around).

 

I will re-cycle your concept on my end for cleaner, less-intrusive and flexible mods.

 

I wonder if these SIP sockets can be cut / ordered to a single-pin, two-pin or any arbitrary pin-# length?

 

@Faicuai Yes, the SIP sockets can broken down to whatever size you need, like @Nezgar said. The problem is that the break is never perfect. There's usually a little bit of left over mass on the broken off bit from the longer strip. This little bit of mass interferes with the spacing against the ROM socket. I could have carefully filed it down so it fits flush with the socket. After that you have to carefully solder the 2 pin socket vertically straight and not cocked to one side or another. That could be little difficult but just be careful. Thinking of these intricacies kind of turned me off from adding the 2 pin sockets but now after sleeping on it I may try this next week

Edited by 1200XL M.U.L.E.
Removing spaces.

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9 minutes ago, 1200XL M.U.L.E. said:

After that you have to carefully solder the 2 pin socket vertically straight and not cocked to one side or another. That could be little difficult but just be careful. Thinking of these intricacies kind of turned me off from adding the 2 pin sockets but now after sleeping on it I may try this next week

Once the 2-pin headers are placed, insert any 28-pin IC to fill the existing 24-pin socket + hold the 4 new pins in place. Then you can solder the 4 pins from the underside with confidence that they will remain straight and not fall out either with the board upside down.

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1 minute ago, Nezgar said:

Once the 2-pin headers are placed, insert any 28-pin IC to fill the existing 24-pin socket + hold the 4 new pins in place. Then you can solder the 4 headers in place with confidence that they will remain straight.

 

@Nezgar That's a great idea! The 28 pin chip would indeed hold the extra 2 pin sockets in the proper position during the soldering process. Thanks for the tip! Now I am definitely going to try this next week.

 

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10 minutes ago, 1200XL M.U.L.E. said:

 Ohh! You clip those through-hole leads from the RF modulator? That's a little too destructive for me, even if I never plan to use the RF modulator ever again. The mass of the modulator scared me a little bit. I would need to heat soak the connection due to the mass absorbing so much heat. That would heat up the board in parallel. Maybe I can try removing one connection and see how it all goes.

Alternately, you can use an iron, flux and solder sucker or wick to clean the through holes from around the leads, but the giant thermal mass of the RF can is working against you. A vacuum desoldering pump will make short work of them, however.  Frankly, I cut them and toss the can. Analog TV’s are nearly impossible to find around here and becoming harder to scrounge with each passing month; good ones, at least. And RF on the 1200XL is terrible. But it’s your machine so do what you want. 

 

In any case, the method I suggested for the solder pads will work fine. I’ve used that technique on many of my own Atari consoles and computers, including two of my 1200XL’s with no damage to the PCBs. 

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23 minutes ago, 1200XL M.U.L.E. said:

That's a little too destructive for me, even if I never plan to use the RF modulator ever again.

Keep the RF modulator in place, if you can. It will give the overall best composite output, color-wise (Less fringing, less ringing, albeit noisier) and you can run it through external or dedicated RF-to-Composite de-modulator, in case a brutal wave of nostalgia suddenly kicks in. 8-)

 

In any case, with the advent of SOPHIA (native DVI i/d output from Atari), almost all analog-stage mods. become essentially meaningless (much better to keep the host HW intact, and protect its value or integrity). Sophia will be your primary video output (digital-to-digital) and stock's analog video will serve as fall-back for Artifacting & frame/color blending, only when needed and provided your video-path can handle it all, elegantly.

 

 

 

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Well I have completed the OS mod chip swap by using 28 pin sockets and they drop right in. Modding a 1200XL for a myIDE upgrade, or was it a 512k upgrade i forget.

I used Component carrier sips for the 0 ohm resisters which would make it a little easier if you need to revert back to original. And you can just put the original chips back in the correct pin sockets.

 

Peace fellow 1200xl dude!

 

Douglas

 

albeit I was a couple of drinks into it but here are my pics of the bare 1200XL MB that I took. 

motherboard.zip

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4 hours ago, 1200XL M.U.L.E. said:

@rockdoc2010 Wow, that is very cool! I haven’t seen a bare 1200 XL board like that. Where did you get it?

Most likely from Best Electronics, they used to sell it but no longer available.

The following is from the Best Catalog Addendum:

Atari US 1200XL Bare Motherboard PCB  CO60585  Sold Out

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