Originally Posted by Rog
Originally Posted by IcePack
Good work Roger. As a matter of interest, did you manage to find what had caused the original fault on the PCB ?
Thinking that it would be either a component failure or dry joint/track continuity fault. Both should be an easy fix. However if the fault is impossible to find their in shows the problem of these type of faults.
I haven’t actually confirmed the original fault yet Bob. However I have quickly powered the pcb up on the bench and can see that the fault it still there, the fog light is permanently on. It appears to be using a regular 2n3904 transistor as a switch/driver for the fog light relay coil and that looks like it may have failed in the on state. I’ve ordered up a few transistors (15 pence each, ouch!) and have a few diodes here just in case too. It’s low priority at the moment but would like it back working as it gives me the option to swap back. I will report back!

For anybody with the dreaded ‘stuck on’ rear fog issue, a bit of an update re the faulty PCB.

My board is looking like it has suffered a couple of failures. The first snag was the 2n3904 transistor that drives the fog relay coil had failed on. The fog relay and it’s snubber diode are fine so whipped the tranny out and stuck in a new. Unfortunately that only made a partial improvement. The ‘stuck on’ fog supply was now at least off, however actuating the fog light switch does nothing. That ‘clever’ latching logic appears to be shot as I cannot detect any control voltage on the base of the transistor despite the board still having its 5v supply working . The control tracking winds its way back to the microcontroller so maybe there's a partial micro failure too, unless I’ve missed something obvious? If it’s the micro then this add a new twist and an obstacle for home repair frown

If... I can maintain the enthusiasm I’ll put a Pickit 3 on my Christmas list and attempt to salvage the hex file and flash a new chip, that might be fun. Assuming of course that it hasn’t been locked…. ooo

The offenders
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Testing the fog light
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Roger
2011 Plus 4