Modem I & Modem I B differences?

[IBM Portable PC]

One is grey and the other white, however, is this the only difference?

Also, does anyone have a 1 B Service Manual?

 

[Petrofsky]

The big difference is that the Modem IB lacks the unusual ability of the original Modem I to be used through the TRS-80 Model I cassette interface (with no expansion interface nor RS-232 interface of any kind).

Haven't seen a service manual, but it should be less mysterious than the Modem I, as it's just a standard RS-232 <-> Bell 103 device, not doing anything Tandy-specific.