So, one of the main problems on my 2004 TD6 is that in various lighting conditions I can't read the speedometer and other gauges, nor is the little green display very bright. With the lights on, the little lighting control turns the lights from very dim to off, and there seems to be too little backlighting at all times. Some warning lights are OK, including the gear selection lamp

I can't find much in the way of videos or descriptions of how to check any of this, so here are the questions:

1. Does replacing or even checking the 5 backlighting bulbs involve taking the whole console out?

2. Is it simple to replace the bulbs with led's?

3. What does the phototransistor shown in RAVE do? If this had blown, could it leave the backlights permanently dim or bright. I have tried shining a torch at it after midnight and it seems to have no effect on the lighting.

4. If I chickened out of replacing bulbs myself, can anyone guess what sort of cost I should expect if I took it to a specialist indy to get it done? Old 110 2.3 Petrol ???? - ????
Old 110 200tdi ???? - 2004
1996 Discovery 300tdi 2004 - 2015 met fiery end being welded
2004 JEEP Grand Cherokee 2015 - 2017
2004 L322 Td6 2017 -

Q1. Yes.
Q2. Not sure about the speedo/ rev counter bulbs, but the pixel readout yes they can be changed to led's.
there was a chap whom did the new ribbon on the pixel readout, he converted them to led's, weather that was for the clocks I don't know.
Q3. If the photo transistor is the little sensor above the hard nav button, try giving it a clean, worked on mine. Other than that, I don't know.
Q4. Don't know of anyone, other than the chap above who does them.
someone else on here may know better.
Hope it helps a little.

Thanks, that is helpful, if a bit depressing, as I was hoping not to have to dismantle the facia in the third week of having the car.

Not the sensor I was thinking of. Didn't know there was one their.
the hard nav button resides by the information screen, the phone and music buttons are below .
the sensor is right at the top of the row of buttons (hard).
I don't think that's your problem though, as the sensor dims thr screen at night.
Sorry, I have no more ideas.

I think the dial back lights are surface mounted LEDs already, but as above the LCD backlights are bulbs which can be replaced. That being said, led replacement don't give off the same even light as filament bulbs so the back ground of the LCD is uneven ... Sometimes it looks crap basically.

The backlight brightness is all controlled by the LCM unit. Are all the backlights of all buttons dim on the dash like the cluster? I.e Heater controls etc?

Is so then more likely to be the LCM power transistor ... Basically digital current controller which feeds all backights throughout the car and the output is controlled by an input voltage signal from the dial at the light switch.

It is in theory possible to replace the MOSFET transistor... I once find a source of them years ago, but never committed to the swap out of my failing one. It would involve some decent soldering. V8 or else ...

It had to go dark to check the lights....

I've been reading up on LED's and I now think they might be a step too far at the moment. I will need to find the precise spec of any bulbs behind the console, though.

Yes the backlights of the heater controls are dim. So dim that I didn't realise they were backlit. Their lighting is controlled by the dimmer knob, but like the speedo etc., just from dim to off.

I see that the LCM unit is mounted in the A-frame. Now, I know this will sound stupid, but which is the A-frame? Is it just in front of the driver, just behind the driver or behind the back seats? I assume it's in front of the driver as nothing else looks anything like an A.

A long, long time ago, I was a sort of electronics engineer, but I always thought cars, vibrating and damp, were a stupid place to put electronics.

I might be able to solder replacement transistors in, but it fills me with horror. I see the headlights etc are also driven by MOSFET's, but I haven't found any mention of the panel lights and their power supplies at all. Neither can I find any pics of the insides of an LCM.

Oh dear, it sounds as though this might be expensive. Old 110 2.3 Petrol ???? - ????
Old 110 200tdi ???? - 2004
1996 Discovery 300tdi 2004 - 2015 met fiery end being welded
2004 JEEP Grand Cherokee 2015 - 2017
2004 L322 Td6 2017 -

The MOSFET was about £10 I think because you would only be buying very limited qty. Couldn't tell you what the part number is, I read it off the top of the chip itself, then googled it for ages to find a source.

The MOSFET had a few large legs to solder to the board along with the base of the unit itself being soldered to the board as well from behind. I honestly think its a doable proposition if you have reasonable soldering equipment to flow solder. If you look at the circuit diagram of the lighting circuits in the RAVE manual, it is possible to follow that from the pin number on the connector, along the circuit board to the correct MOSFET. The circuit lines are large enough to do that by eye.

As for the LCM unit's location, its tucked in behind the trim of the footwell to the right of the accelerator pedal (on RHD vehicle). It just bolts to the bodywork at the bottom of the A-pillar. Once out, it comes apart fairly easily with a few screws IIRC.

As I say, its been quite a while since I had mine out to look at it. .... it looked like this:

Click image to enlarge

Thanks for the pic, it looks like something I could possibly take on, although I haven't actually got any hot air flow-soldering equipment "yet". I have occasionally used friends to help service smt electronics.

I'm still intrigued by the phototransistor in the speedo panel that's mentioned in RAVE. In some ways, a failure of this in a way that lets it signal a permanent "DIM" to the auto-dimming might give the symptoms that I have, but there seems to be little info anywhere about this component.

I would have thought that a power MOSFET would be likely to result in no instrument lights or full brightness rather than the dimness that I have, but I haven't yet had time to dig out the LCM and have a look at the actual beast for burning, whiskering and so on.

The main problem, having only had the L322 for 3 weeks and having bought it knowingly in "sold as seen" condition (but with a large amount of recent garage bills), is that I'm trying to guess what needs to be tackled first to keep it on the road, so I may have to get the clunks and broken bits sorted before dismantling the electronics. I'm too old to tackle much mechanical stuff now, so most of that will have to go to the professionals.

Thanks again Fisha, that's been a great help. Old 110 2.3 Petrol ???? - ????
Old 110 200tdi ???? - 2004
1996 Discovery 300tdi 2004 - 2015 met fiery end being welded
2004 JEEP Grand Cherokee 2015 - 2017
2004 L322 Td6 2017 -

Again, its a long time ago, but I *think* that each of the MOSFETS contain multiple power circuits which are paralelled up to increase the power ... you can see this from how multiple legs are soldered to a single circuit board track. It could be possible that some of the paralleled circuits aren't working ... so reduced brightness. When mine went, it flickered in brightness, and then ended up very dim for a long time.

As for the brightness sensor ... no idea ... I cant recall ever thinking/noticing that brightness of the lights varied with the ambient light.


I also dont recall from the circuit diagram that the sensor had influence over the input to the MOSFET ... I would need to go back and check. V8 or else ...