On units that have serial #s T1631 to T8279, there will be a circuit board that is raised above the left side of the TX1 board. This is the TX4 board. This board holds the audio controls for the Lead 1 Red mode. It also holds some of the switching related to the Lead 1 Red mode. Some units before serial# T1631 have been upgraded and will have the TX4 board. After serial# T8279 the TX4 board was removed. On units after serial # T8279, there will be a small circuit board that is raised above the TX1 board. This is the TX5 board, with four 5C9 LDRs on it. These LDRs, combined with 5C9 LDR #s 26, 27, 28, 29 on TX1, replace the four original Dual Cell (P873) LDR #s 26, 27, 28, 29 that were on TX1. These control the Gain, Treble, and Bass.
In other words:
Units with serial #'s T0001 to T1629 are Version 1 w/o Midi/recording out circuit upgrade
Units with serial #'s T1630 to T8278 are Version 2 w/ TX4 "Vintage Rectifier" Lead 1 red circuit and Midi/recording out circuit upgrade
Units with serial #'s T8279 and up are Version 2 w/ TX5 "Phat Mod" Lead 1 red circuit and Midi/recording out circuit upgrade
Furthermore, you have the best version in my opinion. I hate the T8279+ units. I actually played on T8279...new first new one
.. hated it. hahaha