Kjmann's S-Video upgrade revisited - Atari 400

[Magic Knight]

OK

 

After some apprehension, i tackled the procedures to upgrade the 400 to S-video and it worked first time.

 

However the instructions i found were a little hard to follow when the pictures 'appeared' to be different to what was described! all credit to kjmann for making this avialable in the first place.

 

As some on this forum in the past have had issues getting this to work - ive described below my own brief comments to get this working, this is to compliment the good work done already and ive proved a link to kjmanns download (from the website) to get before trying this. http://www.karaokepo...her/400svid.zip

 

First heres pictures to go by:

 

Luma wire - connect as shown on kjmann picture

chroma wire - connect as shown on kjmann picture

 

Resistors:

The position of the resistors to tack onto the back of the board was easily done. My exact values were 10 ohms out - due to availability issues - a 510 ohm resistor works just as well as a 500 here - same for the 250 and 125 which were 240 and 120 respectively. Now add the short link also.

 

Capacitor:

This is absent from Kjmanns picture - all you need is a 16v 22uF cap - i find its best to use tantalum types instead of the chunky electrolytic ones which are less reliable for this type of purpose (just my opinion). Its basically those yellow capacitors with a polarity marked + on it.

Connect the + to the end of the chroma wire you connected to the board and the other would go to your monitor (see my picture of the test wire-up i used)

 

Luma - 75ohm resistor - this makes a significant difference when present - as the luma give a bright feel - adding this gives a nice deep blue for notepad/basic screens (which is ideal as a reference to see where you are ) one end goes to the end of the wire tap on the board and the other to luma out (to your monitor). adding the resistance will bring the brightness down. My picture has a 240 ohm trio of resistors in parallel (giving a 3rd of this @ approximately 80 ohm)

 

Tip: - for best results - use a 75ohm resistor in line with a 50 ohm pot - you can then get your minimum 75 ohm but increase as required to tune the luma as required (i didnt need it but some machine may benefit).

 

ground for signal - use the marked earth points on kjmanns picture - there plenty others on the board.

 

Audio - unless your really nostalgic and like having no volume control - unplug the internal speaker. Use a wire from the audio tap on kjmanns picture and locate the earth points shown (theres plenty others on the board) you can then use the audio tap for the signal and the ground from the various points.

 

The video looks amazing although my photo doenst do it justice.

 

I will probably tackle my 800 and 800xl as the monitor composite does really look poor compaired to this - i hadnt noticed until now.

 

cheers

 

Rich

Edited February 19, 2013 by Magic Knight

[Awch]

Magic Knight,

Thanks for the instructions. Do you mind clarifying something for me. I was under the impression that Kjmann's upgrade was a circuit board that included different installation instructions for each 8-bit. However, I get the sense from your posting that between Kjmann's 400 instructions in the zip file and your instructions here that there is no other circuit board or components. Is that correct?

 

Am I making any sense?

 

Thanks for your help. I'm really looking forward to installing this upgrade!

 

Thanks,

Greg

[Magic Knight]

When i was trawling the web for improvments for the A8's, i came accross both the add-on board you mention and also the more direct motherboard method.

 

From looking at the components on the add-on, it looks like the same components more or less and wires that tack on the the appropriate areas on the board. This is ok when the soldering is perfect etc, but increases fluxuations if dry joints or intermittant wires occur over time - also a space needs to be found for this board.

 

 

 

we are looking at:

 

510 ohm resistor

240 ohm resistor

120 ohm resistor

75 ohm resistor

16v 22uF capacitor (Tantalum)

S-video lead (for video) or extra composite phono)

phono lead (for audio) - optional.

small wires - like 26 -28 awg wire

sleeving for insulating joints

switch (optional)

50 ohm pot (optional) - for trimming luma signal

 

time takes around 45 minutes - moslty opening up and reassembling the case together.

 

I forgot to add - the part in the instruction about cutting the two tracks wasnt needed where you are using s-Video (as opposed to composite) - i think this is for workability when switching between the two, but i didnt need to do this. As composite may be the only choice for some, the instruction to revert by joining luma/chroma should be observed carefully.

 

 

The XL series look easier as it invloves the inline capacitor / 75 resistor and just disconnecting a couple of resistors (just a snip by cutters).

 

the main page for the zips are found here: http://www.karaokepo...nd.com/svid.htm

 

 

If theres interest in users doing this mods and are struggling to get the parts or they are getting charged silly handling charges from some companies, i may put a few kits up on ebay avalable for a small cost (components/wires/audio/video cables).

 

As theres no Atari 800 mod, im will be tweaking around to find what works and i can post this also here.

 

 

 

cheers

 

Rich

Edited February 20, 2013 by Magic Knight

[+orpheuswaking]

http://www.karaokeportland.com/svid.html

 

You missed the l from the end

 

What does the optional switch do?

[Magic Knight]

thanks - that copy and paste for you!

 

it switches between composite and s-video - the 75 ohm resistor is needed to calm the signal down on s-video but is needed when composite (Luma+Chroma) is chosen.

 

if using composite - you would need a phono jack instead of the 4 pin s-video.

Edited February 20, 2013 by Magic Knight

[YAGRS]

I forgot to add - the part in the instruction about cutting the two tracks wasnt needed where you are using s-Video (as opposed to composite) - i think this is for workability when switching between the two, but i didnt need to do this. As composite may be the only choice for some, the instruction to revert by joining luma/chroma should be observed carefully.

 

Thanks for this bit of info! I plan on doing this mod soon (as soon as the parts come in), and I was a bit leery of cutting the tracks. Since I'll only be using S-video, it's good to know I won't have to cut them.

 

If theres interest in users doing this mods and are struggling to get the parts or they are getting charged silly handling charges from some companies, i may put a few kits up on ebay avalable for a small cost (components/wires/audio/video cables).

 

If I had only waited a couple of days . . . I found this mod online on Monday and ordered the components. Because the mod says that the resistors have to match the values exactly, I spent a long time trying to find 125 ohm, 250 ohm, and 500 ohm resistors, finally buying combinations that I could use to get these values (planned to putting a 120 ohm and a 5.1 ohm together, a 220 ohm and a 30 ohm together, and a 470 ohm and a 30 ohm together). It would have been nice to just buy a kit that had exactly what I needed and saved a lot of wasted time.

[+bob1200xl]

You should know that resistors have a tolerance, 10%, 5%, whatever. So, if you buy a 120 ohm, 5% resistor, it can be anywhere from 126 ohms to 114 ohms. Adding a 5.1 ohm resistor in series doesn't really give you 125 ohms.

 

Just use the nearest standard value 5% resistor - 120 and 240 ohms.

 

Bob

[Magic Knight]

You should know that resistors have a tolerance, 10%, 5%, whatever. So, if you buy a 120 ohm, 5% resistor, it can be anywhere from 126 ohms to 114 ohms. Adding a 5.1 ohm resistor in series doesn't really give you 125 ohms.

 

Just use the nearest standard value 5% resistor - 120 and 240 ohms.

 

Bob

 

quite right,

 

The function of these is to reduce the resistors on the opposite of the board - so the 250 ohm on the top side with one on the bottom (now in parallel) , drops the top value (if identical values - by half). Having a 50 ohm pot in line with the luma would allow this to be trimmed if there were any short commings (and allow you control of how much de-saturation you want).

[YAGRS]

You should know that resistors have a tolerance, 10%, 5%, whatever. So, if you buy a 120 ohm, 5% resistor, it can be anywhere from 126 ohms to 114 ohms. Adding a 5.1 ohm resistor in series doesn't really give you 125 ohms.

 

Just use the nearest standard value 5% resistor - 120 and 240 ohms.

 

Bob

 

I should know a lot of things, but it's surprising how little I really do.

 

I actually was aware there was a tolerance, but because the mod makes a point of specifying exact values, I went ahead and tried to match them. My knowledge of electronics is pretty basic, and I'm pretty much a novice at modding, so I try to follow directions as closely as possible.

[+bob1200xl]

Yes... you need to know when to hold 'em, and know when to fold 'em, and when to walk away...

 

Following Directions is good - take a Reality Check once in a while.

 

Bob <== built his first transistorized amplifier in 1960.

[Magic Knight]

I tried the 800xl mod tonight and worked great, i didnt need to cut the resistors on this one (as suggested) and the resistor value being dropped to 47ohm (instead of 75 ohm) actually made no notable difference. knocked up a pcb instead of tacking components on this time.- a much cleaner install.

 

Next up is the 800...

[YAGRS]

Well, I managed to do this mod tonight without destroying my 400 (though I thought that I might have for a bit, as I couldn't get the mod to work with a 5-pin DIN as I had planned). The colors don't look quite right to me playing Q*Bert, but that may just be my imagination (I should compare it to the colors from the RF output, except that means I would have to open everything up again to reattach the cable).

 

Anyway, I'm happy with the mod. Even if the colors are off (which may not be the case), it's certainly better than staticky, fuzzy RF.

[BillC]

Well, I managed to do this mod tonight without destroying my 400 (though I thought that I might have for a bit, as I couldn't get the mod to work with a 5-pin DIN as I had planned). The colors don't look quite right to me playing Q*Bert, but that may just be my imagination (I should compare it to the colors from the RF output, except that means I would have to open everything up again to reattach the cable).

 

Anyway, I'm happy with the mod. Even if the colors are off (which may not be the case), it's certainly better than staticky, fuzzy RF.

The resistors affect the brightness, if the colors are off(not just brighter/dimmer than they should be) it is likely the potentiometer on the CPU board needs adjustment. The 400 does not have to be completely dis-assembled to adjust this, but the top of the case needs to be lifted up or removed. As viewed from the back there is a small hole in the aluminum shield near the top right, a small standard screwdriver inserted through this hole should be able to adjust the color pot

[atari8warez]

I spent a long time trying to find 125 ohm, 250 ohm, and 500 ohm resistors, finally buying combinations that I could use to get these values

 

You could get all in 250 ohm like these ones and connect two in series to have 500 ohm, and two in parallel to get 125, and the remaining resistor will give you 250 ohm. They are sold in 5's so one batch will do your job. They also have 0.1% tolerance so they are pretty accurately rated at 250 ohms.

 

Edit: I guess I had to read the rest of the thread before replying, it appears you have already done the upgrade... What kind of problem you had with the 5 pin DIN?, I've just upgraded my 600XL with a variation of kjmann upgrade + the DIN connector. All you need to do is to connect the Luma and Chroma lines plus the ground to the appropriate pins of the DIN connector. You could also bring the Composite signal and audio if you wish. Composite is as easy as combining the Luma and Chroma with a 470pf ceramic capacitor in between them.

[Magic Knight]

The resistors affect the brightness, if the colors are off(not just brighter/dimmer than they should be) it is likely the potentiometer on the CPU board needs adjustment. The 400 does not have to be completely dis-assembled to adjust this, but the top of the case needs to be lifted up or removed. As viewed from the back there is a small hole in the aluminum shield near the top right, a small standard screwdriver inserted through this hole should be able to adjust the color pot

 

Thanks for the tip - i noticed only minor differences between my machines, but discounted them as im using a mixture of Pal and NTSC machines and PAL/NTSC cartridges to test. Probably best to use the colours off Altirra to get the benchmark for adjustment. (or a pre-modded machine depending on how much you rate emulation colour interpretation).

[YAGRS]

The resistors affect the brightness, if the colors are off(not just brighter/dimmer than they should be) it is likely the potentiometer on the CPU board needs adjustment. The 400 does not have to be completely dis-assembled to adjust this, but the top of the case needs to be lifted up or removed. As viewed from the back there is a small hole in the aluminum shield near the top right, a small standard screwdriver inserted through this hole should be able to adjust the color pot

 

So that's why that hole is there. That's actually where I ran my wires for the mod, but I think I can still get in there to adjust. Thanks for the info!

 

As for the problems I had with the DIN, I'm not sure. I was using a cable I bought that ended in 4 RCA plugs, three of which I snipped off to connect the S-video (I was using one of the three for ground instead of the ground in each wire, so maybe that was the issue). I used a multimeter and though that I had everything hooked up correctly, but it wouldn't work for me. I disconnected from the DIN and attached an S-video jack, and it worked. It had to be the way I wired the cord, but I gave up trying with the DIN after the S-video jack worked.

 

Oh, and thanks for the recommendation of using Altirra, Magic Knight. I just downloaded the emulator, so I'll try this out this weekend.

[Tempest]

it switches between composite and s-video - the 75 ohm resistor is needed to calm the signal down on s-video but is needed when composite (Luma+Chroma) is chosen.

 

if using composite - you would need a phono jack instead of the 4 pin s-video.

I have Kjmann's S-Video mod done to my Atari 800 (by Sal himself) and while the S-Video is amazing, the composite is sucky. There's some shadowing on the letters and some color fringing as well. The switch doesn't seem to help, it just makes the picture brighter or dimmer. Is there a way to fix this?

[Magic Knight]

I have Kjmann's S-Video mod done to my Atari 800 (by Sal himself) and while the S-Video is amazing, the composite is sucky. There's some shadowing on the letters and some color fringing as well. The switch doesn't seem to help, it just makes the picture brighter or dimmer. Is there a way to fix this?

 

The resistor limiting the strength on the Luma may need to be removed. Perhaps the switch does this on the circuit on Kjanns version of this. or a switch between 75 ohm (400's) and 47ohm (XL/XE) may not be enough when mixing the two signals.

 

The (other) 75Ohm resistor from the Chroma leg to ground can should be removed temporarily to see if its the cause. My laptop PSU sometimes interferes with the circuit (slightly) and the grounding of the chroma (via the resistor) makes it worse.

 

Composite needs all the help it can get as its connecting Luma to Chroma and the signal strength seems to suffer or variable depending on your atari.

 

 

Rich

[Kjmann]

Well, I managed to do this mod tonight without destroying my 400 (though I thought that I might have for a bit, as I couldn't get the mod to work with a 5-pin DIN as I had planned). The colors don't look quite right to me playing Q*Bert, but that may just be my imagination (I should compare it to the colors from the RF output, except that means I would have to open everything up again to reattach the cable).

 

Anyway, I'm happy with the mod. Even if the colors are off (which may not be the case), it's certainly better than staticky, fuzzy RF.

 

Hi There. I just noticed this thread.

 

as far as the 400 goes the resistors that you put in are to help boost the luma signals coming out of the atari. but because they are are all linked, the resistor values that you use will always effect the other luma levels.

 

Example:

 

Changing the resistor on Luma 1

Will effect (Due to feedback through it's own resistor) the the resistance of Luma 0 and Luma 2.

 

this will cause the colors to look wrong if they are too far off. hence forth you may get too dark or too light of some colors making it look funny.

 

the resistor that I came up with are the closest Resistors I could find that were Readily Available at most component houses to make the picture look as accurate as I could. although they may be off a bit.

 

This was always a problem with the 400 and 5200.

 

the idea with this upgrade was to find a way to make the luma brighter without having to add a 3904 transistor to amp the signal. the circuit already had plenty of brightness, but for some reason atari put some heavy resistors on it and then chose to amp it up again after the fact. Wierd idea in my opinion.

[Bryan]

The resistor ladder values are chosen to generate a proper range of voltage levels without overloading the CMOS driver. They are not chosen for directly driving a 75 ohm video load. That's why the transistor amplifier is there. We can usually get away with improper source impedances when driving short video cables, but ghosting and other artifacts will become apparent on longer ones.

[Kjmann]

The resistor ladder values are chosen to generate a proper range of voltage levels without overloading the CMOS driver. They are not chosen for directly driving a 75 ohm video load. That's why the transistor amplifier is there. We can usually get away with improper source impedances when driving short video cables, but ghosting and other artifacts will become apparent on longer ones.

 

Ah I see. Makes Sence. thanks Bryan. I was not aware of those facts.

Edited May 3, 2013 by Kjmann

[Bryan]

Ah I see. Makes Sence. thanks Bryan. I was not aware of those facts.

Nowadays, the best way to drive a cable is with a video op-amp but I understand how much that would complicate the upgrade.

[biobern]

Hooray! I just got my first Atari 400 (NTSC) in very good condition! And it works! What a beauty!

But what I need is Composite Video. I cannot use S-Video. I'd like to modify as little as possible. Do I really have to cut the two tracks? Magic Knight wrote that it is not necessary for S-Video. Why should it be necessary for Composite? Could you please explain what you did, KJmann? Or did anybody else try Composite without cutting the tracks? Thanks for any answer....

 

Bern

[mimo]

I just use one of these, works well. Don't know if there is any reason that the 400 mod cannot be used like this though

[biobern]

I just use one of these, works well. Don't know if there is any reason that the 400 mod cannot be used like this though

 

You mean that you use this adapter on your Atari 400 with kjmann's Svideo-Mod?

Seems that this adapter is just a piece of wire to combine luma and croma, without any resistors or capacitors, right?

Edited May 9, 2013 by biobern