Simple DIY composite video mod

[Simple DIY composite video mod]

Again, thanks for answering friend.
About the transistors, I used BC548C and BC558B. They are original ones (not Chinese crap). I have two other consoles with other mods that work VERY WELL both in CRT and in this same led tv that I tested here on this post.

One of then is a very very simple thing and works very well. The other uses a CD4050 and transistors (the best I've seen so far till now) but it takes a lot of work to build so I was very interested in this one that you did because the idea looks great. Here are the schematics of the ones that I have used successfully so far in my both CRT and LED TV.
About the cables I tested, both are resistance less than 1 ohm. I even tested your mod with the original 75 ohm RF cable as video cable and also with a good AV cable but the defects are identical in both. In CRT the image is much better but still far from desirable. At CRT, the Trimmer works but does very little. The colors are correct in both Led TV and CRT but are weak, ugly and dark and have vertical interferences. This same led TV that I used in the photos works well in the mods I send attached to this post. The 75 ohm resistor is exactly 75 ohms in the digital multimeter.
Any idea?

Thanks friend again.

[Simple DIY composite video mod]

4 hours ago, simon.plata said:

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.

 

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!

 

[Simple DIY composite video mod]

21 hours ago, simon.plata said:

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!

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

[Simple DIY composite video mod]

4 minutes ago, simon.plata said:

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!

Wow!!! Thanks a lot again friend!! I will try it!!!

[Simple DIY composite video mod]

On 11/21/2017 at 7:24 PM, simon.plata said:

Hi, Here is a schematic and PCB design for the mod made in Eagle CAD. I will fabricate it to replace my generic PCB.

 

 

 

If someone want to fabricate your own PCB, just let me know. I can share the PDF or the Eagle files.

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!!!

[7800 with flickering interference]

I am asking because it would be a valued information to know if the issue appeared after or before the AV Mod. If the  issue were before the av mode, the matter is in the console but If the issue appeared after the mod, the matter is in the AV mod.

[7800 with flickering interference]

Sorry for my ignorance but I will ask.

Did this console use a RF modulator before AV mode ??

Did it haves this issue in RF mode?

[8k games into a 4k CHIPS???? How is it possible??? (ATARI 2600)]

On 9/19/2020 at 1:11 AM, Robson Zandoná said:

Are you Brazilian @pcrock, if you can help me because I don't understand electrical projects and schemes?
I am too

 

 

Please. Send me a private message

[Curious and weirds Atari 2600 carts.]

23 hours ago, Danjovic said:

 

The pins are pulled up by resistors and the switches can push the lines down (when closed). The remaining components are a transistor inverter with speed up circuit at base.

 

 

 

Woww!!! Very very thanks for the Schematics!!! I really wanted it!!! The engeneer loved 8k2 resistors values!! Ahahahhahahah

[Curious and weirds Atari 2600 carts.]

21 hours ago, VW said:

This thread makes me want to take apart my 30 in 1 cartridge.

How do you choose the game on this cartridge?

[Please HELP with 2 in 1 8K DIY CART]

On 9/11/2020 at 9:30 AM, alex_79 said:

Weird. In the Tapper rom that seems to work fine on this board, the next instruction is at $fff9, so both A6 and A5 are HIGH.

 

 

I didn't include it in the schematic (as my goal was just to determine the truth table), but in the pics there's a small ceramic capacitor (unknown value) between pins 10-11 of the 74LS00 and GND.

Could a cap placed there help filtering out transient variation of the /R and /S inputs due to A5 and A6?
And, if so, could it be that it works when A12 pulses LOW, but it's not enough when A12 is steady LOW because the effect of the other signals (A9,A10,A7) are delayed by the extra gate (of the 74LS10) they go through compared to A12?

Sorry for the likely dumb questions. As I've said I only have very basic knowledge about this stuff, but I find it very interesting nonetheless.

Today I made a discovery!
I found out that of all these converted roms, centipede doesn't work on one of my consoles!!

All roms converted by friend alex_79, work on 2 consoles that I have that use TIA C010444 (and also on another one that uses UM6526N) but the Centipede does not work on the console that I have that uses TIA UM6526N.

All other roms work on all three consoles.

That is no matter to me, I plan to change TIA UM6526 to KSC131 or C010444 but is a curious thing.
I also found that the original ThunderGround (By Sega) (4K) game doesn't work on this console either.

When I start, all lives die instantly one after the other and the game is over. Hundreds of other cartridges that I have work normally on this console.

[8k games into a 4k CHIPS???? How is it possible??? (ATARI 2600)]

8 hours ago, Robson Zandoná said:

Good Morning
What PCB did you use for these games would you give me?

I used the pcb below...
The friend alex_79 member here in the forum, traced the schematics.
I converted this circuit to use a 27C512 adding two more switches and now it is able to run eight 8K games. But the bankswitching is the same.. It was not changed..

[Curious and weirds Atari 2600 carts.]

I Found another one.
It is a 4 in 1 
The most interesting thing is that in this circuit, the switches are not SPDT devices as in the in MOST OF THEM!

Here the switches are simple on/off ones.

 

 

[Curious and weirds Atari 2600 carts.]

2 minutes ago, VW said:

This thread makes me want to take apart my 30 in 1 cartridge.

Would be very interesting! I would like to see!

[8k games into a 4k CHIPS???? How is it possible??? (ATARI 2600)]

2 hours ago, Pilot99 said:

I start the tests with the 4 in 1 "27C256_Phoenix_Hero_Kangaroo_Ms pac man" and only Hero don't worked, so I separeted the 4 games and replaced "Hero" with other "Hero" from the 4x1 dump of the thread above, so the 4 games work.

So the roms I sent you haves the same bankswitch scheme as that weird cart?
Then The other ones I sent you might work too.. All of them works in the same board I tested here, so I think if one of them works all other must work too.

[8k games into a 4k CHIPS???? How is it possible??? (ATARI 2600)]

35 minutes ago, Pilot99 said:

The pcb schematics and pictures of the first thread, with the games of the second one is exactly what I have, I think the dumps you send me will not work on this pcb/bankswitch, but I will test anyway.

Please... test it and I will remove the chip from my cart to do the dump for you too.

[8k games into a 4k CHIPS???? How is it possible??? (ATARI 2600)]

18 hours ago, Pilot99 said:

Hello friends, I need the dump of these four 8k games or other dumps (8k games) with the same bankswitch to use on a pcb identical to this post.

Sent you a message.

[Curious and weirds Atari 2600 carts.]

Today, another Surprise to me!!!!!
I found one more cart that DOES NOT HAVE any inverter!!!!

 

The words on the CHIP is:

AT&T ´85
QD27128A2
PGM @ 12,5V
INTEL ´83

 

Tha games into the eprom:

 

Frogger (no brand name)
Box By ACTVISION
Crackpots By PROOM
FrostBite By PROOM

 

It appears that exists a lot of 27XX that does not need any inverter to work on ATARI 2600

 

 

[Curious and weirds Atari 2600 carts.]

9 hours ago, Danjovic said:

Digital Game Selection: By the pinout, most probably be a CD4001

Woowww!! Very Cool idea!!!!

[Curious and weirds Atari 2600 carts.]

14 hours ago, alex_79 said:

The highest address pin (A14 - pin 27) is tied to +5V, so the Atari only "sees" the second half of the eprom. What's in the first half doesn't matter.
Yes, you can put a 27128 in there without modification.
I don't know what's the purpose of those resistors.

 

 

I have another 4 i 1 (4K each one game) board absolutely identical to this one but it uses a 27C128 instead 27C256 and it doesn't have the resistors.

[Please HELP with 2 in 1 8K DIY CART]

1 hour ago, Thomas Jentzsch said:

Got you. The floating pin is not responsible for this, right?

As I told before, this is not the circuit with the floating pin. The board I test the roms haves the pins 4 and 5 connected together. 

[Curious and weirds Atari 2600 carts.]

One More!!!
That is a  4 in 1  (one of it 2k and 3 others 4K). It works perfect.
They use a bigger 27C256 eprom than needed due to be the one they had it in the hands at those days I think.

I attached here the rom dumped from it. The first eprom´s 16K is  all BLANK (FF). How is it possible???
I plan to use that 27C256 in another cart and put a 27C128 here.
My quest is:
What is the reason to use that red pointed resistors connected from pins 6,7,8 to +B ??????????
A 27C128 will work here?

 

27C256_ 4in1 Bowling_Donkey Kong_Kunf Fu_Atlantis.BIN

[Please HELP with 2 in 1 8K DIY CART]

19 minutes ago, Thomas Jentzsch said:

That's pretty odd. Any idea why this is happening?

Just to report. I don't know if this has to do with the problem but on this circuit, pins 4 and 5 of the LS00 are soldered together.

[Curious and weirds Atari 2600 carts.]

7 hours ago, alex_79 said:

Regarding for the "Kangaroo" board, the rom is split into two 4k eproms. The bankswitching logic switches the "chip enable" pins of the 2 eproms so that only the one containing the current bank is enabled.
Some commercial Atari 7800 and atari 5200 games have the rom on separate chips.
And the typical board used for 2600 8k prototypes has two 4k eproms too (here an example).

 

Once more Thanks friend!
But  tell me more please. Haves Each of the eproms exactely a half original rom codes ???
If yes, is possible to changes the roms with two 2732 ones that contains a half of Popeye (for example or any original 8K rom) code each one and it will work???

[Please HELP with 2 in 1 8K DIY CART]

7 horas atrás, alex_79 disse:

Outra tentativa ...

tapper_fa0_v3.bin 8 kB · 3 downloads

WOOOOOOOWW !!! alex_79 !!! O Tapper v3 que você me enviou hoje está funcionando MUITO BEM !!!!!!!!!!!!!!!!!!!!
Sinto muito pelas fotos ruins, mas minha placa ATARI 2.6K está conectada a um dispositivo CRT !!
Estou mandando as fotos !!!
Muito obrigado aos amigos alex_79 e Thomas Jentzsch por me ajudarem na conversão de bankswitching para minha prancha brasileira !!! E obrigado a todos pela atenção em mim e nos meus problemas !!!!!