RT5350 Part I – HAME MPR-A1 Teardown

After removing the three screws, the front cover can be removed.  The clips holding this cover are a bit more tenacious, so you may try prying around the LAN jack while pushing in diagonally on the sides.  The blue plastic sides attach to the outside of the clips of the top cover, so pushing on a side will make that side tighter.  You must push in on one side and pop out the opposite side in order to release it.  Three clips each side, and one at the top by USB hold the cover in place.  Once removed, you see the mainboard below.

There’s the RT5350 in center, with the small 4MB flash just to the right of it, and the larger SDRAM chip to the right of that.  Knowledgeable readers may notice that this device has already had it’s SDRAM chip removed and upgraded to a larger size – again a topic for another article, but the type of chip you want is 32MB or 64MB, 16 bit wide.  These are most often found on 256MB or 512MB PC133 SODIMM (144 pin), which is exactly where this ram chip was harvested from.

Aside from that, we have the LAN magnetics on the far left and a few power management chips spread around.  40MHz oscillator up top and a crapload of resistors and capacitors spread around the device.  The curved trace sprouting up to the top left is the RF output for Wifi, and the large black square at the far top left is the chip antenna.

5_Top_Cover

Fig 5 – Top Cover Removed and Mainboard Exposed.


The mainboard is held in gently by a few plastic clips, and is now easy to pop out.  Be warned when putting the mainboard back in that the vertical part of the flat white button must be pushed back or it will collide with and damage the small pushbutton switch below the SDRAM.  We lost one popping the mainboard in carelessly.

At this point, you can free the mainboard and flip it over to find the RS232 testpoints for the serial console, as shown in Fig 6 below.  This is a 3.3V serial port!   Do not connect it directly to your PC or you will irreparably damage the FT232′s serial console.  Your best bet is using a 3.3V serial to USB converter like this Keyspan one here, or one of the many FT232 devices out there such as the venerable Sparkfun FT232RL Breakout board or clones.  The pinout is shown below – when connecting, you MUST connect GND as well as RX and TX to get communication.  The baudrate is 57600, or sometimes 115200 in oddball devices.

This port is the main serial console – it can always be used as a Linux terminal in order to access the device, even in the case of a bad firmware.  For this reason alone, it’s highly recommended to get yourself some sort of FT232 device to use as a failsafe means of communication on this here port.  It’s pretty easy to solder wires to the pads shown below, but keep in mind that there’s not much extra room underneath the battery so bulky connectors will prevent you from closing up the device after modding.

6_PCB_out_Serial_Port

Fig 6 – Mainboard Removed and Serial Port Pinout

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