VTX Modification History

The VTX has changed relatively little in its life since first introduced on 2004. The best indicator of a controller’s age is the date code hand-written on the board, of the form 06e (or maybe e06) where “06” is the year (2006) and the “e” is the month:

Jan a
Feb b
March c
April d
May e
June f
July g
Aug h
Sept i
Oct j
Nov k
Dec l

Early boards were built by a company who did not do a very good job. In October 2010 we changed the assembly-house to Sub Assembly Services and build quality improved greatly.

March 2006 Build 2
  • R44 was 47K changed to 10K (RAT threshold)
  • R51 was 10K changed to 1K0 (regen c/l timing)
  • R1 was 3K3 changed to 10K (input buffer Vmax limiting)
  • R7 was 3K3 changed to 10K (input buffer Vmax limiting)
  • R18 was 120K changed to 100K (oscillator frequency)
  • R22 was 10K changed to 100K (oscillator – had been an error)
  • R59 was 47K changed to 100K (c/l sensing)
May 2006 Build 3
  • C15 was 330p changed to 100p (high side timing)
  • Q17 MMBTA92 changed to BC807
  • Q19 MMBTA42 changed to BC817
  • Q18 MMBTA92 changed to BC807
  • Q20 MMBTA42 changed to BC817

These are the MOSFET driver transistors. MMBTA42 and MMBTA92 are high voltage transistors (300v). Unfortunately there were timing issues with these (causing excessive MOSFET heating), so we changed back to BC817 and BC807 which are rated at only 45 or 60v on paper, but in practise are around 100-120v and perform much better (far better gain and peak current handling).

This change should be applied retrospectively. But see also build 17

Dec 2007 (Build 11)
  • C15 was 100p changed to 33p
  • Q21 was BC817 changed to BC846 (hiside ‘pole’)
  • R73 was 22K changed to 47K (ignition)

With R73 at 22K, ignition would work down to about 3.7v. Unfortunately at this point th MOSFET switching doesn’t work so a dud battery can blow the controller. With 47K here. ignition switches off at around 7.5v giving some measure of protection.

This change should be applied retrospectively. But see also build 17

May 2008 (Build 12)
  • R64 47K was changed to 22K
  • R65 10K was changed to 100K
  • R64 22K was changed to 10K
  • R65 100K was changed to 10K
June 2013 (Build 17)
  • Q15 was BC 846 changed to BSS 123
  • R64 was 10K changed to link
  • R65 removed
  • C15 removed
  • C4 removed

These changes replace the high side ‘pole’ switching transistor by a small MOSFET. This not only reduces components but also improves the timing of the highside switching. It also makes the circuit less vulnerable to sudden drops in the internal 9v supply rail.

This change should be applied retrospectively.