Page 15
VTX series instructions
part of the circuit board the controller may well fail.
The capacitor can only heat while the controller is
actually working properly so capacitor failure is
always simply down to overloading the controller in
one way or another.
Overheating
If any electrical item is worked hard it can get hot. If
it is overworked for too long it will simply get hotter
and hotter until something fails. Depending on the
nature of the installation and overloading, solder
joints can melt, the main capacitor can vent and the
MOSFETs may then fail. Fortunately such severe
overheating is not common.
Sustained overheating causes the varnish around the
heatsink and capacitors to discolour. This is not in
itself harmful but can indicate problems.
No reverse.
If the controller won't reverse there are two distinct
possibilities:
1
The motor still goes forward when reverse is
selected.
2
The motor is dead when reverse is selected
The first fault is likely to be a wiring fault: the
reverse signal is not getting to the controller. Measure
the voltage on the black wire to pin C (measure with
respect to battery –ve). If this is low (below about 6v)
the controller will go forward. When high (above
about 6v) the controller will reverse. The reversing
switch connects this pin to battery positive to apply a
voltage to reverse it.
The second fault is usually in the controller.
There are many more fault-finding hints in the
service manual available on our www site.
We can repair damaged controllers. But please be
sure that the controller is faulty before returning it as
we may make a charge for handling controllers which
are not faulty or which only have the fuse track
blown.
There is an additional handling charge made if
controllers are returned in boxes. The box itself never
requires and servicing!
Otherwise charges made will depend on the age and
condition of the controller and on the fault as we tend
to be fairly lenient in interpreting the guarantee!
A handling charge will be made if working
controllers are returned for test, or with only a fuse-
track blown.
Make sure you include your name, address and
details of the fault with the returned controller.
Fuses.
Three fuses are present to limit
damage to the controller in the event of a
major wiring problem to the control input.
The main 'fuse' is a zig-zag section of
track shown to the right. It is situated on the
underside of the board, just by the b
connection.
If it fuses, solder a fine piece of wire over
it - a single strand from 7/0.2 cable is fine, but
no thicker! Special pads have been placed for
this purpose. Or use FSR-090 (see 4QD www site).
There are also similar fuse tracks to pins A (F2) & F (F3) of the 6 pin input
connector (far right drawing). Best check these with an ohm meter as visual inspection can be misleading.
In practise fuse tracks are very fickle: it would be possible to design a board with 5 different fuses each
one of which could blow singly and separately under different overload characteristics: we cannot guarantee
therefore that the correct piece of track will always blow! So if in doubt, fit a separate fuse as page 6.
Service
main fuse
F2
F3
