It looks the same, but the inside is different.
There are 2 main types of Nintendo Famicom models.
The previous model is the original model.
The latter model is the one that was improved to cope with the limited amount of noise emitted by the equipment. The functions of Famicom models are the same, but the board in the middle has been changed. The previous model is easier to modify.
How to distinguish Previous model and Later models
Marked on the plate
Look at the left end of the front of the device.
If there is nothing here, it is the previous model, and the mark like FF is the later model.
Connector of the cassette
You can also tell by seeing where you insert the cassette.
If you open the red lid and the connector of the cassette is blue, it will be the previous model, if it is surrounded by metal, it will be the later model.