DR-135 TNC 5V regulator modification

I recently acquired an Alinco DR-135 radio with an integrated EJ-41U TNC unit.
I decided to replace the TNC with an Argent Data Tracker3 T3-135 module. After installing the module, however, the TNC board would not power up.
I measured the 5V line feeding the TNC module at around 3.5V. When I replaced the module with the original EJ-41U, I measured around 3.8V (although that unit seemed to work OK, even on such a low voltage).
Update: If anyone is doing this mod, don’t pull power from the 7808 like I did. See below..
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Netgear GS108T-200NAS Hacking

Netgear GS108T-200

I’ve got a number of these switches in use. They are quite handy as they do not require external power when PoE is available, and have some nice monitoring features.

For a project, I needed to control a non-connected device in a location where I only had the switch and some other closed devices. My first thought was to try to use the switch to talk to a small microcontroller that could drive GPIO lines as required (this way I would not need to take up an ethernet port)

That idea hit a dead end, but I found some interesting undocumented things on the switch, not just on the serial port but on the network as well.

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