A/V mod simply won't work!

[31336haxx0r]

Hey folks!

 

I have a 4 switcher and a Jr. that I wanted A/V mod. The 4 switcher is in a very fine condition, the Jr. doesn't output a stable pic on the RF.

 

I tried the "Lynx's 0,68 Euro ATARI 2600 Junior Composite Mod" on the Jr. first. It doesn't sync properly an a cheap ass ALDI TV, only from time to time, depending on the Lumas and Croma (!!) actually displayed. It NEVER syncs on a Sony Trinitron.

 

Then, I buildt a transistor buffer using this schematic:

http://www.atariage.com/forums/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=104571

 

It didn't improve syncing, except the colours seemed to be more intense.

 

Then, I put a diode in series with the sync line, as seen in several mods, like this one:

http://saundby.com/atari7800mod/7800_vidmod_construction.html

 

It didn't change anything, again.

 

Now comes the 4 switcher. It outputs RF fine. A bit rough, but fine, even with the mod installed (only luma, dind't connect the croma) wire directly to the TIA.

 

I've uploaded 2 images of the TV using RF

 

and A/V.

 

 

So can anyone tell me what the dunkel I'm doing wrong?

[Osbo]

Check this page out, I'm sure you'll find more info and/or help:

 

http://www.cheeptech.com/2600mods/2600mods.html

 

I always did the second mod (Ben's)

[Oge]

What I can say is that some Sony Trinitron(s) have issues with S-Video: if it is not strict to standard, you'll have issues. This modification seems to be a PITA, howewer

 

Cheers,

Oge

[31336haxx0r]

The link to Ben's video mod is dead, but I found this: http://benheck.com/book/support/Atari2600VidMod.htm

Is removing those parts necessary? I didn't.

[31336haxx0r]

I forgot to mention both are PAL systems and I kept the different TIA pinout in mind while modding.

[31336haxx0r]

I just took a look at this:

 

 

 

(source: http://www.dspguide.com/ch23/3.htm)

 

Sync signals need to have a negative potential referring to ground. The best one can get with the usual A/V mods is 0 Volts relative to ground.

Now I have this idea to put 2 diodes anti-parallel from the 2600's ground to the RCA connector's ground to offset the voltage by about 0.3 volts.

What do you think?

[GroovyBee]

Can you take photos of the circuit you made (both sides if its on perf/vero board) and where you attached the wires to on the motherboard. Ideally use a macro on your camera so that everything is in focus.

[31336haxx0r]

Can you take photos of the circuit you made (both sides if its on perf/vero board) and where you attached the wires to on the motherboard. Ideally use a macro on your camera so that everything is in focus.

 

IT FRIKKIN' WORKS!!! I messed up on the build. I accidentally connected the 2.2k pullup resistor to the base instead of +5V! I get a B&W signal. Now I just need to hook up the croma signal.