As per my earlier thread, i replaced the 2n7002 Mosfet on the small board in the rear lamp assembly but just have a tail lamp working and no brake lamp. Any ideas guys?
Thanks
Peter
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Sounds like the PWM dimming function is not working.
Easiest way to test this would be with an oscilloscope on TP2, but after looking at the circuit, its either the 555 timer or more likely the transistor Q2 (A3904 I think - really hard to read) that pulls the positive rail to ground that's shorted (so there is no pulse width modulation - its bright all the time).
Check between R7 and ground - depending on which end you get you'll either get 10K or a few ohms.
Thanks Heath
It does look rather bright allright! I think I will just try to get another board or even a complete lamp assembly! Any Ideas anyone as to where I might find one?
In the case where I am compelled to have existing boards repaired, How does it work?... the Q2 keeps the led array dimmed and when the brake switches are activated the Q2 is taken out of the loop thus giving full strength illumination (brake light effect)?
Sorry for the rather asinine non-tech language!!
Peter
Yep that's basically it. The 555 Timer provides pulses for PWM (dimming) when the brake is applied, the transistor shorts the supply (provided via a resistor) to ground. This turns off the 555 and you get full brightness.
If you get stuck getting parts or fixing it there is someone local here who is wrecking a Vectrix, I could get you the board or full taillight assy.
That is great thanks Heath. I am, picking up a 10 of those transistors today from RS Components Transistor GP BJT NPN 40V 0.2A SOT23 and will see how I get on.
Had the new transistors fitted to Q2 and Q3, the lamp lit dimmed for about 3 secs and then went bright again..... before I had a chance to even try a brake lever. Any idea as to where I might get a board? :-(
Cheers
Peter
Took it apart and visually checked board for burnt components.. could see no damage ....reassembled and it starts dim for about 6 seconds and the goes bright. repeated a few times and still the same. ???
Hi, the symptoms you describe could be caused by a number
of things.... since the symptoms changed a bit when you
installed the new transistors, the next thing to look at
is the input diode(s) (the schematic resides in the Collaborative
Handbook under the tail lights section) specifically D2.
If you are still looking for a replacement board I have
a spare that I would be willing to let go....
PM me and we can work out the details.
Galago