Given that the adapters are so compact, it was difficult to take them completely apart to get a positive ID on all components. And in some cases, the heatsink covering the Qualcomm Atheros parts was not easily removable. Still, the internal pictures provide some good information about complexity and parts count.
As noted earlier, all use the AR1500/AR7400 powerline chipset. They also, however, all use a Qualcomm Atheros AR8021 Gigabit Ethernet PHY and have 16 MB of RAM. As the following photos show, however, all have different physical designs.
Opening up the Belkin adapter provided the view in Figure 4 that isn't very illuminating. But the company assures me that the AR7400/AR1500 chips lie underneath.
Figure 4: Belkin F5D4085 inside top view
The side view in Figure 5 shows a two-board format with lots of power related components that we'll also see in NETGEAR's design.
Figure 5: Belkin F5D4085 inside side view
D-Link's adapter is a single-board design. The powerline and Ethernet devices are on the bottom of the board, covered by a thin soldered-on metal heatsink. The single 16 MB EtronTech RAM chip sits up on top of the board.
Figure 6: D-Link DHP-500AV inside
The inside photo in Figure 7 of the XAV5001 adapter, shows a thick heatsink that's coupled to the main devices via a thick thermal pad. The heatsink isn't tied down; it is held in place only by the top cover.
Figure 7: Inside the XAV5001
Removing the heatsink (Figure 8) reveals the AR7400/AR1500 chipset and Qualcomm Atheros AR8021 Gigabit Ethernet PHY to the lower left. RAM and flash are somewhere on the bottom of the board.
Figure 8: XAV5001 board detail
There is another board on the very bottom of the package, connected to this top board by a 10 pin connector, similar to the Belkin design. The bottom board is where a lot of the AC line coupling and power conversion circuitry sits.
The board photo in Figure 9 shows another single-board design, similar to D-Link's. It uses the AR7400/AR1500 chipset, AR8021 Gigabit Ethernet PHY, 16 MB of RAM (EtronTech EM6A9160TSA) and flash squirreled away somewhere. Note that only the AR7400 has a heatsink.
Figure 9: TPL-401E board
ZyXEL's adapter is another single board design, this time with separate heatsinks on both powerline and the Ethernet devices (Figure 10).
Figure 10: ZyXEL PLA4205 inside
Sorry, but due to the last minute addition of the PLA4225, I didn't open it up for a picture.