I bought a Beige TI-99/4A from E-bay for <$30 (incl shipping).
I built the Composite cable adapter, and it didn't work. I figured the machine was just dead. Then I looked at another diagram and realized I was looking at the wrong end of the DIN plug and had the pins transposed. A quick bit of de/re-soldering and I had a picture (woo hoo!). Even better it is a 1981 OS (y'know... in case I find an Atari cartridge at Goodwill).
Now most of the keys don't work. The connection is (like everything in this machine) very clean. I kept hitting the "1" key until it started to work. The same "method" worked on a few other keys. Seems like this is caused by funk on the key contacts. Anybody know a less-complicated fix?
(pictures to follow - once I upload them from my phone).