Some tales from the workbench, and a request for assistance. First, the story and some background, and then the question(s).
I recently modded a single-chip ATARI 2600 Junior to accommodate a built-in game ROM, as it was designed. Quite simply, if NO cartridge is placed in the console and it is turned on, the console plays the built-in game.
These so-called "unicorn boards" have been covered in a few historical threads here on AtariAge - -
(2011, thread on compatibility with HARMONY cartridge)
(2010, a general thread on the unicorn board)
and, DigitalPress link to the schematics for the single-chip unit - - http://www.digitpres...s/index.htm#vcs
(choose the Atari 2100 "JAN" single chip
link in the list)
Here's my shots from the before-after install. I also added a simple transistor/resistor video mod while I was in there (just mono, no stereo mod, because I didn't want to start pulling pins on the chip needed for AUD0 and AUD1 !)
The motherboard, before adding the built-in ROM, but after installing the video mod
Blank area of the board where the ROM was to be installed at the factory
Detail of the board revision number
I installed a 24-pin socket to receive the ROM
I chose PITFALL! as my installed ROM, and placed it in ANOTHER machine-tooled 24-pin IC socket, which would allow me to stack IC sockets on the motherboard for some form of modularity, in case I wanted to swap installed games on the "unicorn." 4k ROMs are apparently the maximum that the board can take. (See the schematics at DigitalPress and the threads referenced above)
I could think of NO better 4k ROM than PITFALL!, a brilliant use of every ounce of available space!
Socketed in, and all ready to go!
Buttoning it all up . . .
I use some serious "strain relief" in my direct, "corded" video mods to prevent ANY chance of the cord getting pulled and wrecking the electronic work inside!
And, it works! Brilliantly! It plays PITFALL! if there is no cartridge plugged in, and for SOME games, when you load a cartridge, it disables the on-board ROM and you can play the game!
More on that compatibility later - - it's a GIANT topic, and one I also have questions on, and you'll see more posts soon in the general 2600 forum area, and questions on the light/heavy sixers with built-in games, too. There is still some work to be done in order to maximize compatibility, and wire in a "kill-switch" that disables the ROM totally to do so. You'll see this topic again, no doubt!
This, however, is a HARMONY CARTRIDGE question.
Still with me?
So, I popped in my HARMONY cart, and despite what I had read about needing to short certain pins on the cartridge slot in order to get it to work, it DOES boot up.
The menu is skewed, however, and not easily readable! I can navigate the menu, go to sub-menus, and actually even select and launch ROMs . . . but I can't really read what I am doing, and have to operate by memory!
Once a game is launched, there is no more graphical distortion, and everything plays as expected, for at least the half a dozen games I tried from the illegible menu.
Another possible clue to the answers, maybe - - I am using a HARMONY pre-production
cart that I traded with another member to get - -
The SPECIFIC question - -
- What do I do to the motherboard in order to regain what is apparently a graphical issue with this HARMONY cart that I have (the pre-production one) as well as any other HARMONY cart (important!)
Thanks for reading all of that, and I welcome any and all suggestions, questions, and ideas!