NCC Key Components

This page identifies some of the key NCC components. It shows a Mk 1, issue 24 controller. Mk 2 is similar, but uses sub-miniature resistors.

Mk 1 boards issue 18 and later are similar to that shown. Controllers before issue 18 used a slightly different circuit. and are now too old for us to support.

The key components are indicated on the diagram below by a red arrow with a number beside it. The transistors are separately numbered in white (this can be useful if we need to discuss transistor numbers via email) and the numbers cross-refer to the circuit diagram, Tr1, Tr2 etc. PNP transistors (generally BC556/7) are light grey and NPN transistors (generally BC546/7) are darker.

The indicated components are as follow.

1. 9v1 zener.
   This is deliberately chosen so that it has a tendency to fail short-circuit under any overload conditions. By failing thus, it protects other components and is generally good at limiting the damage. Type BZX55C 9v1 or any similar zener of the right voltage.
2. current source ref transistor.
   The zener diode is fed by a current source. This is the sensing resistor. PNP, type not critical, we use BC557C (centre base)
3. current source dropper transistor. Type not critical, we use BC557C, except on the 48v version where it’s a T039 (metal case) with additional heatsink. See NCC and Pro series power and protection mechanisms.
4. current source 22R sensing resistor.
   If you have an accident which blows the current source, the 22R can turn black. Best replace it is if it’s discoloured. And it’s safest to replace both transistors.
5. Hiside driver (NPN) BC337
6. Hiside driver (PNP) BC327
   If you’re into replacing these – you’re getting deep!
7. Loside driver (NPN) BC337
8. Loside driver (PNP) BC327
   Can be blown if the MOSFETs go, if so, the 10R gate resistors (item 26) should be replaced. Check also the 9v1 gate clamp. Usually it’s the PNP driver that goes, the NPN one survives.
9. Gate clamp 9v1. If this is blown, the MOSFETs are certainly dead and the 10R gate clamp resistors (to its right on diagram) will need replacing.
10. Relay drive (NPN) BC546C
11. Relay drive (PNP) BC557C
    The relay drivers are not at all fragile, but they can get blown if an uninsulated motor connection contacts the circuit board. Also, reversing the battery tends to blow both PNP drivers and the catching diodes!
12. Relay drive (PNP) BC557C
13. Relay drive (NPN) BC546C
14. Relay catching diode 1N4148
15. Relay catching diode 1N4148
16. Pot fault transistor (PNP) BC557C
17. Brake catching diode 1N4002
18. Brake driver TIP42A See Adding parking brake drive
19. Overvoltage catching zener, BZX55C 47v on 12, 24 and 36v controllers. BZX55C 72v on 48v versions.
20. The ramp capacitor. See Ramps – acceleration and deceleration.
21. Current limit resistor. 47K here gives a limit of around 55 amps per MOSFET. 22K gives zero current. The relationship between them is linear and is explained for the Pro series (which use the same circuit).
22. Half speed reverse header. Link is shown in ‘half speed’ position.
23. Reverse-ignition diode 1N4148. This is present on later issue boards for the sole function of enabling two push buttons to be used. If you are using separate ignition and reverse switches, this can safely be removed. Because wiring faults can blow this, it was later removed from standard production. On the VTX it can be fitted as a volume factory option.
24. Pole base resistor. This was 10K from issues 18 through to around issue 23. However – with this value the MOSFETs can fail if the battery supply ever fails so that the internal 9v line drops down to around 6v. This resistor is now increased to 22K, and is automatically changed during service.It seems to be the hiside MOSFET (which fail explosively) that dies when this happens.
25. Reverse dwell timing capacitor. May be removed if required.
26. 10R CR16 gate resistors: 4 off on issue 24 et seq. On earlier issues, the hiside did not have gate resistors. We choose this size because they quickly fail open-circuit and rarely burn up.