Pain in the Nethers - Chassis Frustrations -1a - Atlas

DB follows up - 

FYI here are the three versions of the Atlas SD7/9/24/35/etc. 

The 1990s Atlas/Kato one  - they still run well, but the motor had to be isolated to add a DCC chip:

The early 2000s edition was 'DCC friendly' with an isolated motor, and you could unscrew the chassis halves a little to pop out the light board for a DCC replacement. The negative with models of this era was maintaining good electrical connection between the frame and the decoder board (often requiring slim brass shims wedged into the four corners), and between the board and the motor. These models have quite slow speed motors from memory, which was a pain when running them with other locos, which why most of my other diesels have been modified with DCC speed changes to they will run with these slow DC/DBR/DA chassis:

The new one. Black speaker box under the board at right whether you want one or not, little piggyback board under the main board at the left end, joined with an E24 connector (DC here, but these can be replaced with a DCC or DCC+sound one):

On the plus side, while the bogies look identical to the older models (complete with now-redundant sticky-up copper tabs), tiny wires are now used with micro connectors to bring the power up to the board, rather than the old brass strips along the sides. I think the motor is also linked to board with wires, so I may end up throwing away the supplied board and hardwiring an orange decoder into those wires. Of note, the chassis isn't split frame anymore,

With the tiny wires, connectors and components one wouldn't want to drop this on the floor...