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Bryan

Quick & Easy Video Upgrade for 800XL

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The Super Video upgrade makes a big difference in video quality, but you can get most of the benefits with this simplified procedure. Most 800XL's will look like the ones pictured here (the later ones with Freddie are different and already have Chroma-out). I've attempted to use only stuff you can get at Radio Shack (though I personally hate to go there). :)

 

edited Apr. 21, 2009

 

Modifications:

 

L5 & new power lead

The same trace that brings 5V to the video circuits also powers the clock oscillator circuits. 1 clock circuit for NTSC, and 2 for PAL. The shared power route can cause faint vertical bars to appear in the picture. The purpose of inductor L5 was to deal with this noise, but it doesn't really do enough.

 

Remove L5 (or at least lift one leg of it out of the board). This will break the old 5V path.

 

Solder a wire from the front lead of C3 (electrolytic to the right of the power jack) to the front hole of L5 (or to the front lead of C51 next to it). If you run this wire along the RF modulator, it should clear the shield. 20 or 24 gauge wire should work well.

 

C56

For some reason, Atari decided to add this cap which blurs the image. This capacitor is not present in all 800XL's. If it's not there, then great. If it is there, then remove it entirely.

 

R116

The Q3 luma amp is an emitter-follower type. The large collector resistor reduces the gain of the amp a bit too much. Place a 10-ohm resistor across R116.

 

R53

If you have a 390-ohm resistor (orange, white, brown) here, solder a 100-ohm resistor across it. If you have a 100-ohm resistor here (brown, black, brown) then you may leave it alone, or solder a 330 ohm resistor across it if for a small luminance improvement.

 

The ideal resistance here is 75 ohms. When video drivers deviate from the 75-ohm standard, it causes an impedance mismatch with the coax cabling and the monitor which degrades the picture and can cause ghosting (reflections) in longer cables.

 

Chroma Feedback Resistor

Solder a 1K resistor from the bottom of R58 to the right side of C55. This will improve color somewhat.

 

Missing Chroma Output

On the bottom of the board, solder a 100-ohm resistor to the junction of R67 and R68. These two adjacent resistors run left to right and their junction is on the left when looking at the top of the board. Put a piece of tape under the resistor to insulate it from the board. Solder a wire from the other end of the resistor to pin 5 of the DIN connector (bottom-left pin from the back).

 

the resistor can also be soldered on the top of the board and a wire run to the jack as in post #2

 

Optional: Power Filtering

I have removed this step. The current scheme of an electrolytic bypassed with a monolithic is sufficient once you run the new power wire.

 

I've attempted to show the improved picture, but it's hard to get a good digital snap of a monitor.

 

-Bry

 

 

 

A picture of this modification is posted on page 2 of this topic.

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Edited by Bryan
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By the way... If you have a DIN connector with the pins exposed in the back, you can solder the chroma resistor and lead wire on the top side of the board (as shown), saving some time. The correct DIN conductor is the 4th from the left, 2nd from the right.

 

-Bry

post-3606-1073716004_thumb.jpg

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It compares very favorably with my Super Video 2.1 machine, and if you've got an 800XL with the 390 ohm R53, you'll notice a huge difference since it's off by a factor of 5, and causes very weak output!.

 

-Bry

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C56

For some reason, Atari decided to add this cap which limits sharpness (& blurs the image). This capacitor is not present in all 800XL's. If it's not there, then great. If it is there, then remove it entirely.

 

by low-pass filtering the luminance you can avoid that luminances affect the chrominances. this reduces/removes color artefacts.

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C56

For some reason, Atari decided to add this cap which limits sharpness (& blurs the image). This capacitor is not present in all 800XL's. If it's not there, then great. If it is there, then remove it entirely.

 

by low-pass filtering the luminance you can avoid that luminances affect the chrominances. this reduces/removes color artefacts.

 

then should I not remove that cap?

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C56

For some reason, Atari decided to add this cap which limits sharpness (& blurs the image). This capacitor is not present in all 800XL's. If it's not there, then great. If it is there, then remove it entirely.

 

by low-pass filtering the luminance you can avoid that luminances affect the chrominances. this reduces/removes color artefacts.

 

Later machines (like XE's) don't have it, and the 400/800 used a much gentler filter (33pF instead of 180pF). Anyway, it's effect is too dramatic to be beneficial, and C54 is the cap that does the job properly.

 

Compare the video with and without it, and you'll see why Atari eventually removed it.

 

-Bry

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Can I use this modification on PAL XL?

 

Yes. The video circuits are the same (and reading down, I see you discovered this). :)

 

Also, for clarification: Except for C56, leave the original parts in the board and piggyback the new part on top by bending the leads down and soldering to the existing part.

 

-Bry

post-3606-1073758679_thumb.jpg

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when I test R11 it it reads @ 380 ohms @ 5%

 

additionally if it is supposed to be @ 75 ohms would you think that I could just go out and but a 75 ohm resistor @ 5% and throw it in there?

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when I test R11 it it reads @ 380 ohms @ 5%

 

additionally if it is supposed to be @ 75 ohms would you think that I could just go out and but a 75 ohm resistor @ 5% and throw it in there?

 

Why are you testing R11? It's part of the audio circuit.

 

Yes, you could put a 75 ohm resistor in R53.

 

-Bry

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Can I use this modification on PAL XL?

 

Yes. The video circuits are the same (and reading down, I see you discovered this). :)

 

-Bry

 

Cool, this mod looks much easier than super video 2.1 mod.

Thanks for the info.

 

Matthias

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for L5 whats the propper resistance?

 

To work properly, it should be only a couple of ohms, but the cheap inductors Atari used have a resistance of about 10ohms (measure it out of circuit). All the power to the video circuits flows through that inductor.

 

Here are some pictures I just snapped of an unmodified 800XL. The picture is not as sharp, and a bit washed out.

 

-Bry

post-3606-1073768786_thumb.jpg

post-3606-1073768787_thumb.jpg

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Hello,

 

is the modification necessary for french atari 800xl SECAM ?

 

 

-Arnaud

 

I've never the schematic for a SECAM XL, so I have no idea. :)

 

-Bry

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I just went out and bought a bunch of resistors, My collection was getting a bit scant. They are all 1/2 watt resistors. will that be good enough for this mod?

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could I get a bigger picture the underside of the C56, Because when I removed it I noticed that the two componets on either side of it were solderd together. and I'm not sure if there is supposed to be a connection there, or if I screwd up.

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could I get a bigger picture the underside of the C56, Because when I removed it I noticed that the two componets on either side of it were solderd together. and I'm not sure if there is supposed to be a connection there, or if I screwd up.

 

Here's what my board looks like on the bottom-side of C56 (800XL Rev A2):

 

-Bry

post-3606-1073788338_thumb.jpg

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