Hi,
I recently bought a standard 4/16 MB TT-RAM board manufactured by ATARI on ebay.
According to this: http://www.geocities.ws/SiliconValley/Peaks/6320/ard/help/ttram01.htm
"TT RAM chips must be 30 pin 1Mb or 4Mb x 8 non-parity nybble mode SIMMs.
The 8 means 8 chips on each memory card, NOT 9 or 3 they will not work."
I set up the expansion correctly for 16 MB and have 4 x 4 MB SIMMs (but 3 chips on each).
But while the first TOS test indicates 16 MB of TT-RAM is detected and fine, later when using machine can I randomly get 2, 4 or even more bombs with TT-RAM attached. I've also run a test-program for TT-RAM (attached by someone on this forum) and it screams (in German! 
) with thousands of errors...
Is the RAM organization on SIMMs to be blamed (3 chips on each, not 8 )?