75Servo4-F Bldinst2c.doc 3 of 4 Issue 2c June 2012
Testing.
You will need a standard analogue or digital multimeter to test this module.
Switch your meter to a resistance range. Connect the black meter probe to terminal 5 of J6 and test for
continuity of the 0v rail around the board by touching the red probe on the outer pins of J2-J5, pin 14 of U1 DIL skt
and pin 5 of the D-connector J7. Continuity is confirmed with a reading of 0 ohms on a digital meter or full scale
needle deflection on an analogue meter
Connect either a 12Vdc supply or a 9Vac supply to J1. Please be aware that lightly loaded power supplies
can deliver substantially higher voltages than specified. If this occurs then Servo4 components will be
damaged, particularly capacitor C1 (eg using that auxiliary output on a Gaugemaster controller is known to
overload C1) so please measure your intended source with a multimeter BEFORE connecting your servo4
module. The specification for input of 12Vdc or 9Vac is not to be ignored. When happy with the power
supply, switch your multimeter to a Vdc range and check the voltage on the middle pins of J2 – J5 against the pins
nearest the edge of the board. It should be 5V. Check that the main regulator U2 is not getting hot which would
indicate a short somewhere. If it does, disconnect power immediately and troubleshoot. If all is OK, remove power.
This module is provided with a subsidiary 5V voltage regulator U3 which supplies power to the onboard SRV4 PIC
U1 in order to minimise the effects of any noise generated by the servos. It may be connected in either of two
ways, only one of which must be chosen:
a. to the main power supply through J1, as above, in which case LK2 C-2 must be made with a wire link and the
main power supply then powers the whole module, or
b. to an optional independent external 12Vdc supply (such as available from some CBUS modules or the DCC
Steady State Decoder kit 53) connected at J6 (positive to J6/6 and negative to J6/5, diode D1 protects against
incorrect connection), in which case link LK2 C-1 must be made. The main power supply at J1 then only powers
the servos whilst the subsidiary power supply at J6 only powers the PIC.
With power off, install your required link at LK2. Reapply power and check that regulator U3 is not getting hot. If it
does, switch the power off immediately and troubleshoot.
When satisfied and with power connected, use the multimeter to check for 5Vdc as follows. With the black lead of
your meter to J6/5, check with the red meter lead at the positive terminal of C3, at pins 6 and 8 of 'D' connector J7
and pins 1 and 4 of the empty DIL socket for U1.
If all is well, disconnect power supply, ground yourself (touch a water pipe or radiator, for example) and insert the
SRV4 microcontroller U1, ensuring that it is correctly orientated ('bite' to 'bite') and that all legs are entered into the
socket. Press firmly home. Switch the power back on and recheck the voltages as above.
If all is OK your Servo4-F board is completed. Please read the notes on connecting servos before proceeding.
Notes on Connecting Servos
Servo Cable Colours
While the Futaba colour coding appears to be the most common, be aware that other manufacturers and re-
badgers use other colours. If you view the cable with the black to the right, the core should be as follows:
Manufacturer Control Positive + Negative 0v
Futaba white Red black
Hitec yellow Red black
JR Radio Orange Red brown
Tower Pro SG90 Orange Red brown
Unhelpfully, Airtronics buck the near standard: view the cable with red to the left.
Control
red black Black or white
Servo4 Power-up
Whilst the Servo4-F module is capable of driving most model aircraft servos, some brands have a tendency to
twitch on power-up thus possibly straining connecting links to layout accessories. It has been determined that this
feature can be ameliorated by applying either a pull-up voltage bias or a pull-down voltage bias to the servo
