The page detailing modifications to the 4QD series controllers mentions a 'current limit bounce clamp' as being fitted to issue 9 and later top boards.
This page details how that modification may be retro-fitted to issue 03 through 08 controllers. The problem was never noticed until issue 08 and in consequence has never been retro-fitted to other than issue 08 controller, but should be OK back to issue 03 inclusive.
This modification was not fully incorporated to production board until issue 10. Issue 09 had the modification partially included.
The circumstances under which this modification is needed are quite rare: the problem only occurs when the vehicle to which the controller is fitted is being accelerated hard so that the current limit is engaged during acceleration.
The only vehicles where this has occurred are all go-karts. It is not likely to be a problem elsewhere and is not a 'required' retro-fit. We do not automatically fit it on service returns.
The drawing above shows the modification.
You will require:
| 2 off | 10K resistor | 1/4 or 1/8 watt |
| 1 off | PNP transistor | BC556 or similar |
| 1 off | Diode | 1N4148 or similar |
| length | hookup wire |
The drawing above should be clear enough. BC557 has a centre base and European style lead outs. These are identified as B, C, E in red. If using an American 2N series transistor, be aware that the collector and base are likely to be transposed.
The transistor's emitter connects via the diode as shown. Base via a 10K to the 22K resistor at bottom of drawing. Collector via a second 10k. It is convenient to solder the floating end of this to the '4' of the 4QD logo where shown, as anchorage.
Two lengths of hookup wire complete the modification, as shown in red. On factory modifications, the assemble is held in place by conformal coating, but you can apply whatever non-conductive adhesive you see fit to anchor the bits to your satisfaction.