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Atari, Retro

Atari 2600 Jr PAL AV Mod

Atari 2600 Jr

Atari 2600 Jr

Or should that be a Simple Atari 2600 AV Mod?

No. No it shouldn’t. You see, the Atari 2600 Jr 2600 PAL AV Mod should have been simple. On paper it was simple. Upon construction it was simple. Did it work though? No.

What’s this all about then?

Well. I wanted to be able to hook up an original Atari games console to my Projector, for big screen retrogaming. I didn’t want to mod my original 6-switcher, or the 4-switcher, or the Vader come to think of it. So I chose a spare Atari 2600 Jr for the task.

If you have a Google for an Atari 2600 Jr PAL AV Mod, you’ll probably only come up with results for NTSC machines – with a small throw-away line about how it will probably work on PAL. Hmmm….

Anyway, let’s go through the simple, painless, it took me a whole bloody week to get it working process, and then possibly help others out there who are looking to do this without spending too much time or money.

A very simple circuit

First of all, apologies to whoever made this diagram. I downloaded a PDF from I don’t know where a couple of years ago. I can’t find it online anywhere now, so I can’t credit the author. If you know, please let me know, so I can do the honours:

Atari 2600 Jr AV Mod – Circuit Diagram

Simple huh? I can do that. It’s only 3 components. I have those components. I also seem to not be able to pay attention though…

Simple AV Mod Circuit
Simple AV Mod Circuit

Before hooking this up, apparently, you need to remove some components from the board. I would say read this blog right to the end before removing anything – then decide!

Out with the old

My usual gung-ho approach here, I just followed what I read before really thinking about it. So I removed the RF box, L8, Q4 and R56:

Atari 2600 Jr PAL motherboard
Atari 2600 Jr PAL motherboard

Then I connected the bottom pin of Q4 to +5v In, top of R56 to Video In, the silver trace on the board is ground and audio comes from the bottom of the resistor on the left in the image shown here:

Atari 2600 Jr PAL motherboard wiring
Atari 2600 Jr PAL motherboard wiring

The outputs went to 2 phono sockets, one for audio, one for video.

Job done?

Nope. Nothing. Well, almost nothing. I got audio, but nothing more. I stared and stared and stared at the circuit for days. In the end I realised I’d wired it up incorrectly! The components were okay, I’d just put a couple of wires in the wrong place!

I rewired it and tried again. Still nothing! Then I realised I’d got the wrong value resistors. Seriously. How much of a botch job can I do on this? I had 330 and 220 ohm resistors, instead of 3300 and 2200 respectively. D’oh!

Atari 2600 Jr PAL AV Mod – Take Two

So, I rebuilt the circuit. Very carefully, with the correct values and the wires in all the right places:

Atari 2600 Jr PAL AV Mod rebuilt
Atari 2600 Jr PAL AV Mod rebuilt

Very nice. Soldering on the back was lovely. Take my word for it. Everything was perfect. I hooked everything up, plugged in a cartridge, switched it on, and…. Nothing!

I put everything away in the cupboard and gave up.

Then I took it out of the cupboard again. I’d found a reference to various luma signals I could try and add to the chroma signal – where the yellow wire was currently hooked up to the board. So I unhooked that cable and touched it to the various luma points. I could see flickers on the screen, so I knew the console was doing something.

Once more unto the breach…

So I found these instructions, on a site so old and so not live any more that I could only access it via the Wayback machine: https://web.archive.org/web/20040218081408/http://www.hwcn.org/~ad329/2600vidm.htm

This was basically telling me I could do the mod without any components!

On the bottom edge of the circuit board is the chip that controls the Luma and video sync. It’s labled MSM 3980 0Z66 on mine. The pins are as follows. Pin 2 – sync. Pin 5,7, and 8 – Luma.

These pins can most easily be accessed by soldering a lead to the tops of resistors R217, R215, R214, and R216. Connect all these leads to the centre tap of an RCA connector. Now you’ve got a Luma signal (for use with a monochrome composite monitor or a high quality colour composite monitor that accepts individual Chroma and Luma signals).

This didn’t quite match what I had on my board, but after touching the yellow cable to various points on the board, I determined the 4 places to connect some wires to:

Wiring diagram
Wiring diagram

So wire the first 3 resistors (shown above), miss one out and then that big resistor, to the top of R56. Then connect your yellow wire from the top of R56 to the phono plug – and hook ground to ground. Excuse the dodgy soldering in that image. I just wanted it done!

Phono sockets
Phono sockets – audio and video

See the way I cunningly threaded the wires for the phono sockets through the old RF socket? Saves drilling holes in the case of the Atari 2600 Jr.

Eureka!

Guess who can now play Pacman on his Projector?!

Atari 2600 Pacman
Atari 2600 Pacman

So after a week’s worth of faffing about, all it took was 9 wires and 2 phono plugs! Good enough for me.

Conclusion

So I hope you read all of this before diving in. What I will say is, if you have an Atari 2600Jr PAL console that you want to AV mod. Just try this final solution first and work back from there. I’d be interested to know if you need to remove any components at all.

I hope my trial and error approach has been of use to someone!

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