[Dr_C]

When Scalextric developed the C8515 rev H decoder they increased the motor/brake drive circuits from circa 1 Amp (as used in rev F and rev G) to 2.8-3.5 Amps. They did this by introducing the AO3434 MOSFET for motor PWM and the AO3401 MOSFET for brake actuation. The AO here refers to the semiconductor manufacturer Alpha-Omega.

In my view, upgrading a standard Scalextric decoder with excessive levels of MOSFET current drive would simply mean that other parts fail first in the event of a short circuit. Even worse if these are difficult to replace parts or cause damage to the circuit board itself. On this basis the AO3434/AO3401 is likely the ideal combination for the Scalextric decoder designs.

Another point worth considering is that Scalextric use MOSFETs which are specified to 30V (Vds_max). Some make the mistake of overlooking this specification parameter and advise a downgrade to 20V. Here we need to keep in mind that due to the use of inductors within the design of the SSD powerbase, a nominally 12V SSD track signal can have voltage spikes up to twice the value (i.e. 24V), so a device with a 20V limit is simply inadequate.

So to cut a long story short the repair advice which follows will use the AO3434 and AO3401 as replacement MOSFETs. These are Scalextric recommended (as per the rev H decoder) and likewise my recommendation for upgrading rev F and rev G decoders).

Photos of the repair procedures to follow.

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