simon.plata

October 10, 2020

5 hours ago, pcrock said:

I just tested in LED TV. The results were very very very very BAD!!!! ahahahahah

I tested both consoles with the same AV cable, same power supply, same LED TV and same cartridges! The one that uses the CD4050 AV mod works very impressive well!!! But the one with the AV mod we are discussing here shows a very poor quality screen with a lot of interferences and ghost. Now I can see that even in CRT tv, the interferences exist (not so bad as in LED screen but it is still there).

Below I post the last pics about the AV circuit from the friend Simon.Plata

Below I post the issues at LED TV

Below I post some Pics from the console using CD4050 AV mod. Very clean, great colors and sharp graphics. If you see any issue in the pics below is from my cellphone camera. Actual graphics is very impressive good! The black Background is very clean with no interferences or noisy issues.

If someone have any idea, I really would like to use the circuit from friend Simon.Plata.

Thanks

@the_crayon_king made a very good point, you could still have audio signal interference. Did you removed ALL the components indicated in the instructions?

Otherwise audio signal could still have a path to mix with video. Also, the indicated components needs to be removed in order to leave a clean chroma and luma signal. The RF oscillator is still in place? Or was removed?

I believe all the above makes sense because both the mods you referenced as working properly, are taking signals directly from TIA pins.

Bests,

October 9, 2020

8 hours ago, pcrock said:

Hi friend. I did the mod and all ran ok on building the circuit but unfortunately the results was not good.

About the transistors I used BC548 and BC558 instead 3904 and 3906 that are unusual ones here in Brazil.

I attached pics to show you the image issues to ask if you could give me some idea.

For the trimmer I tried from 0K to 10k but had no bright change. The image is dark and full of interferences and contours blurry.

The console is in NTSC mode X200 (xtal) is 3.579545 MHZ

I have great interest on this mod.

Once more special thanks friend!

Ok, Colors and saturation looks good, then I can say the mod is working properly. The issues with the image are related to gosthing and image post processing by the TV DSP.

BC548B/C and BC558B/C are good replacements. Be sure there are BC5x8B or C, the last letter defines de hfe of the transistor. Letter A or no letter are low gain devices.

I suggest the following:

The 75 Ohm resistor is very important. Be sure it's 75 Ohm +/- 5%

The video cable is the responsible of most of the problems. Please ensure you're using a good video cable and connectors. Check cable resistance, should be less than 1.5 Ohms. Check ground.

Try to find a CRT TV set (old TV) and check the video image on it. Several new LCD/LED TV sets have several image processing algorithms that can distort the video. If the gain change didn't affect the brightness, it's an indication that the TV DSP is normalizing the video and further post processing is being done.

After checking the image in a CRT and tuning the gain, go to your LCD/LED TV set and disable ALL the image processing or enhancing features. This should improve the image.

Let me know how it works for you.

Bests,

October 9, 2020

4 hours ago, pcrock said:

Please tell me one more thing.
Is it correct 10K for R9 (audio) ???
It appears too much high value to me.
thanks again

Typical audio line input impedance is 10K and line output impedance is 100 or 600 ohms. Due to short distance of the cable in comparison to the wavelength, impedance matching is not required.
For maximum audio signal level you may choose 100 to 600 ohms for R9. However I prefer to use 10KOhms (same as line input) for short circuit protection and to avoid input saturation.

Please let us know how it works for you and the video results.

bests!

October 8, 2020

58 minutes ago, pcrock said:

Hi friend!!! Great post!! I will do that!! Very thanks for sharing with us!!
Please tell me. What is the way to get the BEST trimmer adjust ??
Thanks again!!!

Hi,

I’m pleased you find it useful.

First of all the trimmer only adjust the gain of the amplifier. That means it varies the brightness of the image only. Ghosting and other distortions are not related to the trimmer adjust, but to impedance matching.

The best trimmer adjust could be seen from different standpoints.

One of them is obviously according to the NTSC or PAL standard. Which is 714mV Or 700mV between the black and white level correspondingly. You will need an oscilloscope and a test cart to generate a color bar test signal.

My favorite adjust point is which “Looks” better in your TV set. I use to set the TV at factory settings for video. Then I adjust the trimmer until I get the more pleasant image. Lower than optimal gain will give a dark image but well defined colors. Higher than optimal gain will give an overdrive signal. The brightness isn’t increased but the yellow will change to white. Optimum gain should be near maximum brightness but having well defined yellow.

Hope it helps!

November 22, 2019

On 11/17/2019 at 5:56 PM, slaanesh said:

@simon.plata I will try a higher value cap as you suggest and report back my findings.

If anyone else has any other suggests to change the mod I'm willing to try on my PAL Atari(s).

However I would need a circuit diagram (or mods to the above ones) so that I can build the board

The current mod I am using has a pretty good vibrant display. It's not perfect and there is still some ghosting but it's better than RF cable and of course more convenient to connect to TVs and monitors. I using a Samsung 940MG 19" LCD- which is good because it has loads of inputs including RF, composite, s-video, component and RGB SCART.

HERO PAL-60 version on my 4-switch PAL Atari.

You can see the Activision logo looks fine however there is ghosting. My 10K trim pot is turned right down. This is with the 47pF Cap in place.

Ghosting could be produced by overdrive of the video signal, try to reduce the gain an see if the ghosting persist.

If it persist then could be a mismatch of coupling impedance. Try a different video cable and different lengths the shortest the better.

November 22, 2019

On 11/17/2019 at 2:42 PM, ChildOfCv said:

Yeah that fits my hypothesis then. The input impedance of a common collector amp is going to be less than gain*load resistance, around 7.5K in this case, at best. That's a pretty large load for the resistor ladder, and explains why you typically remove the RF modulator in that case.

The Atari module that I mentioned replaces the 2N3906 with a MPSA13. This is a Darlington transistor which has the same pin package and configuration but gain is advertised at 10,000. So the input impedance should be closer to 750K. That transistor also seems to be fairly cheap and common. So perhaps it could be used in a cheap and simple common-collector solution.

It sounds like a good idea. My concern is about the bandwidth and roll-off frequency. Darlingtons tends to have multiply the base-emitter capacitance of the hidden base, but should give a try.

November 17, 2019

On 11/15/2019 at 1:40 PM, ChildOfCv said:

It might be faster and easier to design for an op-amp that's intended for video amplification though. Something like this:

https://www.maximintegrated.com/en/products/analog/amplifiers/MAX4395.html

It sounds like you have better than cookbook-level experience with electronics, so I'm also curious why you went with the common-emitter approach, when the Atari seems to have enough voltage swing out of the gate, so no gain needed. Is it just because a common collector didn't have enough input impedance? (though the Colecovision Atari module mitigated that problem with a Darlington pair transistor).

Hi ChildOfCv,

In respect your first comment, you´re absolutely right . It's really easy (nothing to do really) to design the mod using an integrated video buffer in place of a discrete one. Indeed I ordered some video buffers to do another AV-mod for my VCS consoles. In this case I selected the TSH122. https://www.st.com/en/amplifiers-and-comparators/tsh122.html

However the objective of this post, was to give an easy to built AV-mod which really works and was affordable for almost everybody in the world. In some places it's not easy or affordable to order uncommon electronic parts. Also I wanted it to be possible to assembly in an universal PCB or even a bread-board.

Regarding your second comment, I might don't really understand your question. However I will try to respond. In the first post of the tread, I exposed two options:

The first one is a one stage amplifier in common-collector configuration, which is the best approach as you said.

However, given the high output impedance of the resistor network DAC (about 10.9KOhm), the current gain needs to be into the hundreds, which is in the edge of the capabilities of a general purpose transistor at 4.2MHz.

The second one is a modified common-collector configuration like the first one, plus a preamplifier stage in common-emitter. I choose the common-emitter configuration for the preamplifier to take advantage of the high input impedance and the convenience of embedded biasing of the common-collector second stage.

I hope I have responded to your question appropiately, otherwise please let me know your comments and I will try to do my best.

November 15, 2019

12 hours ago, slaanesh said:

@simon.plata what would be required to modify your board so that it works more comfortably with the PAL spec?

I'd be willing to make another board

Hi @slaanesh,

PAL requires a higher video bandwidth (5.0MHz) than NTSC (4.2MHz), and this is the reason why you get the better results with your trim-pot all way down, which is the point of the highest gain for the circuit.

To optimize the circuit for PAL's signal, it’s needed to move the knee point or the roll-off frequency point to the right (Higher frequency), which requires a complete redesign of the circuit, because it its DC coupled. The roll-off frequency is the result of the superposition of the RC low pass filters formed by the transistor's parasitic capacitances and the input/output equivalent resistances.

You may try to change the C1 capacitor from 47pF to a higher value like 68pF or 100pF to increase the gain in the high frequency end. That trick could work but it’s not warranted.

Unfortunately I’m being too busy at work, otherwise I would try to redesign the circuit with PAL bandwidth in mind. I will try when I have a truce from work.

November 14, 2019

1 hour ago, slaanesh said:

I made my own board today to replace tfw8b AV mod which was too dark for my liking. I used a 10k trim pot as I couldn’t get a 5k one.

My Atari is a 4 switch Vader PAL model. On first boot I was pleasantly surprised to find that it worked but I had some smudging across the screen - adjusting my trimpot all the way down solved this.

Great mod I am very happy with this thanks@simon.plata also thanks to @Djoulz as I used your diagrams to build my board.

Hi @slaanesh, I'm pleased it worked for you. It was designed for NTSC so the optimum gain could be in the edge for PAL.

Also I want to thanks @Djoulz for making it easy and accessible for more people.

April 14, 2019

Hi and thanks to everybody who tryed this mod.

May be I forgot to suggest to adjust the trimmer until you obtain the better picture in your set-up.

The calculated value is for 0dB gain and 1Vpp output which is the standar composite video signal span. However due to the tolerance of the components in the VCS board and the in the mod, it could be lower or higher than that. The trimmer was included to correct that deviation.

Best regards and enjoy!

April 14, 2019

Quick update on the simple composite mod I made to my 4 switch woody. As I said above, picture looks great on a CRT, and on most older (non-smart) LCD panels. HOWEVER, there are big image problems when sent to my 1st generation 4k LCD HDTV. While the color seem solid, there are major ghosting/double images occurring, no matter what settings I change on the TV itself. I blame the ever-worsening analog to digital chips in these newer TVs, which apparently can't quite cope with the hack's timings/signal strength.

Hi stlouisrod, have you tried to reduce the gain of the amplifier?

Gosthing could be produced by several factors, including unmatched impedance and overdriven signal. The RCA cable could increase the impedance and generate gosthing.

I tested it on different LED TV and I have got nice video image.

Best regards,

April 14, 2019

By the way, the link to the mod is lacking tha "a" at the begining so is not working.

Here is the correct link: http://atariage.com/forums/topic/271678-simple-diy-composite-video-mod

Enjoy

April 14, 2019

Hi mogul345, thank you for posting my mod in your list!!!

Just one coment: my mod comes in one and two transistors versions. However two transistors version is better.

Also I posted the PCBs if someone want to fabricate it. I wanted to fabricate a lot and have them available but due to my work I couln't ship them quickly.

I have the Eagle files and would be fantastic if someone could fabricate a lot and sell them online.

Best regards,

September 27, 2018

Update: I removed the 820p and 47p caps in the right red section of your diagram, with no change to the picture. I also tested the 2N3904: emitter to ground before trim pot = 1.1v; after trimpot adjusted for best saturation of picture = .95v. So it seems well within tolerance. Even if i adjust the trimpot to lowest level (highest resistance), the picture gets dim but the pixel coloring anomaly remains. So it never appeared to be a low current issue, and now I've proven that electrically as well.

Despite the mod is just a simple video amplifier, it exists several reasons to not work properly: One of them could be amplifier saturation to any or both rails.

The real problem can't be found easily without an schematic or a signal analysis with an oscilloscope.

The alternative is to revert the mod you did and try with the mod proposed in this tread which is proven and has worked for several people including myself.

Best regards,

September 25, 2018

Thanks a ton for offering to take a look. Here are the pertinent pages from the install manual of my mod:

The mod you're installing is not the same as the one stage (one transistor) posted in this tread. From the information you send it's very difficult and time consuming to reconstruct the schematic in order to analyze the circuit and verify the configuration.

However it looks like a bandwidth issue or a unwanted low pass filtering. This could happen because:

* The 2N3904 transistor is out of specs or in the lower limit for gain. I suggest to test it for a minimum gain of 200 or replace it.

* May some of the minimum removal components are still in place. These components needs to be removed from the VCS board, otherwise they Will attenuate or filter the signal to unusable levels for this mod.

If neither of the above Works for you, I suggest to implement the mod posted in this tread, then we can offer better support or advice.

Bests,

September 24, 2018

Thanks for your continuing assistance!

The transistor is riding at least a centimeter above the PCB, so little chance of interference there.

I also don't think it's interference, as the color issues are VERY consistent and repeatable. They don't waiver or fade like RF interference causes. This appears to be a definite rounding error or color-clock translation issue, which likely a diode or transistor issue not resistor or RF issue.

It's not a chip issue, as I swapped all 3 chips from my unmodded 4 switch unit that had good display.

Colors don't "shift over time". They are present exactly in same games, same conditions, from power on to power off

I've added more pics of the exact issue below. Please ignore the weird reflection in upper right of each pic.. my "Game Room" neon sign was on behind me.

Hi,

Can you share the schematic and component values you're using? I Will give a look and see if I found something.

Looks like a bandwidth problem, it could make a color shift or distortion.

Best regards,

May 21, 2018

Hi, can be installed on PAL Light sixer too? I see that this circuit best suits NTSC... seems to be better than this one https://www.thefuturewas8bit.com/shop/atari/atari-composite-video-mod.html

Hi, it was designed for NTSC bandwidth in mind which is a bit lower tan PAL. However "boggis the cat" used it on a PAL 2600A and worked fine (please see entry #11 above). That means it supported the PAL bandwidth. It should work on a sixer. Only needs to identify the components needed to be removed and the corresponding connection points. The two stage transistor design worked very well for me over all other single stage that I tested before.

March 24, 2018

This looks fantastic.

I have been using an A/V mod that I purchase off eBay https://www.ebay.com/itm/Atari-2600-7800-A-V-Composite-RCA-Audio-Video-Mod-Kit-NEW-IMPROVED-KIT-1G-/311705759237?_trksid=p5731.m3795

I have been pleased with it so far, but I am always looking for something potentially better. I am planning to install your design in a light 6'er as soon as I can get all the components together.

If possible I would like to get a copy of your PDF Eagle file.

Thanks.

Hi,

Please see the PDF files attached. Sorry for the delay.

VideoAmp2S_MSK.pdf

VideoAmp2S_SLK.pdf

Best regards,

March 8, 2018

I'm gonna go for it too, but I have to collect some parts first. Looks promising!

Darryl

Hi Darryl,

Good to hear you will give it a try. Please let us know if it works for you.

Regards,

Simon

February 24, 2018

Hi,

Give a quick look to my post: http://atariage.com/forums/topic/271678-simple-diy-composite-video-mod/

May be you like it.

Regards,

January 16, 2018

Well, I got this installed. I have to tell you this is the best picture I have seen on a 2600. Great job with this!

The previous single transistor, 2 resistor composite mod I was using had a terrible picture. It was dark and had static patterns. It looked bad on my big flat screen and barely passable on a CRT.

This two-transistor circuit is like night and day..It looks very clear without any static or noise and is plenty bright with nicely saturated colors. It was easy to build too thanks to the schematic and board layout as well as the above pictures. Thanks again.

Norm

Hi norm, I'm very glad it worked for you!

Thank you very much for your kind comments. I'm happy making a little contribution for the 2600 community!

Best regards,

Simon

January 11, 2018

Hi,

I did this fix using a thin piece of metal sheet from a food can. Thin metal sheet is easy to cut with scisors or a dremel and a cutting disk.

Not a CX40 but may give you some ideas. I did this fix several months ago and the joystick still working like a champ.

The donor:

December 12, 2017

Good Job! :thumbsup:

November 27, 2017

I used a couple of the cheap AV mods a while back on my 2600 Vader and my 7800. The mod worked out great on the 7800. The picture is very clear and there is no color bleeding.

On my Vader (4-switch, revision 12 board), the picture is, well, terrible. There is quite a bit of color bleeding and it makes most of the text or scores, unreadable and some games are so much of a mess that they hurt my eyes.

I recently bought a 2600 Jr. that I intended to use the RF on, since the picture is fine. The issue is, I'm running into a lot of compatibility issues with different TVs. I bought the Jr. because I wanted an Atari that was easier to transport to friends homes and such, but a lot of new TVs just won't work with the RF signal and carrying a VCR around is worse than just carrying my 7800.

Now here's what I'm wondering..

Isn't the Jr similar to the 7800, as far as how the video output is handled? If so, shouldn't the cheap mod work just as well on it as id does on my 7800?

I know that the 7800 uses a 4050 chip and I'm guessing that has something to do with the cheap AV mod working and the Jr. has the same chip, right?

I also know that the Vader doesn't have this chip and the cheap mod doesn't work as well. So.....

(I hope I'm making sense and not just rambling. )

If I'm right, I'm thinking about pulling the mod board from the 4-switcher and using it in the Jr. Then buying a mod kit that is better suited for the 4-switcher.

If my thinking is correct and the cheap mod will work fine on the Jr, What mod should I install in the Vader/4-switcher?

I have heard nothing but good reviews on the UAV mod and it's the only one that people have been talking about lately. I also read a post from a few years ago about a mod that uses the 4050 chip, but the circuit was really complicated to build and I'm not the best at soldering.. So, what's the recommendation?

Hi, I posted a simple video mod I did on my Vader/4-switcher board. May it could work for you. Simple and cheap: http://atariage.com/forums/topic/271678-simple-diy-composite-video-mod/

November 22, 2017

Hi.

Thanks for these. That board looks just slightly neater than my two efforts (The first of which decided it wouldnt work, so the one you see it my second improved attempt!) Shifting the breadboard circuit to protoboard was trickier that I had assumed, transistor pinouts being uncooperative.

Just a note that R5 and R6 may be best to have a couple of pads available. I used a 33R and 43R in parallel to get ~18R for R5, and two 150R in parallel to get 75R for R6.

This would require shifting the pads out and take a little more space, but would make it easier for people who dont have the exact resistors to hand.

Yeah, good advice! I will take it into account for the next revisión. I didn't know these resistor values were not easy to find everywhere, I selected these values because they are into the estandar 5% values.

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