Electronic experts!!!!

Guys, is there anyone out there who may be able to explain the wonderful circuitry associated with the SPEEDOMETER?? I have recently had the usual speedo problems and have tried the usual fixes described on the forum with mixed success.
I have had periods where it has been OK for days and then others where it is intermittant over various miles. The one thing that I have noticed, is that when the speedo is not working is that if I switch something On and then Off, such as the heated rear window, heater blower or the central locking switch then the speedo starts working again???
It has to be a quick on and off, switching either of these on and leaving them on doesn't make it work. I have also tried switching other things, such as the lights, radio or window switches and they have no affect either.
It always works with these others, which makes me suspicious of the circuitry - are there any transistors that could be affected by this sudden surge? Does anyone know what the circuit board does on the speedo console where the speedo plug attaches. Any suggestions will be most welcome.
Thanks,

Jeff

Can't advise on the circuit but I used to find that I could get mine to start working by switching the ignition off and on - whilst on the move if possible. So your theory about the dropping voltage could be right. Its almost like there's some sort of latching arrangement whereby if it doesn't get a certain voltage or signal within a certain time after starting then it just gives up until the next time its started, or its power supply dips and surges enough to make it think that the car has been started.

I'm sure I've seen posts on this forum before that discuss the circuit board and how one of the chips is a custom chip that nobody can fathom out (but my memory could be playing tricks on me)

Jeff mine used to do the same thing with blower or window. If you think about it both cause a big voltage spike and yes, that can seem to bring it back to life.

The whole instrument pack uses extremely low voltage signals so according to a mechanic I was talking to recently he found the only way to effect a permanent fix was to go through the entire speedo loom, remove all the plugs and clean solder everything together. That way all the dry joints and potential voltage drops across the push-fit connectors are removed.

However it's a GTA speedo so who knows! Anyone here who saw the 'Watchdog' article about Audi TT instrument packs tonight must have laughed their head off.

LOL....


How about all Alpine owners call the Audi helpline and see what suggestions we can get out of them, perhaps one will work for us.
As for 600-720 for a new speedo, that makes the Alpine one "cheap".

I sat saying 'its just like my Alpine!' to Trudy and chuckling. Weren't they all getting very upset too..bunch of gimps!!! We just laugh about ours

They drive a TT what do you expect ,bunch of stockbrokers

Well I am an electronics designer, but not sure that makes me an expert.

Would suggest that a logic section in your speedo is locking up, turning a high demand 'other device' on is causing either a spike or voltage drop that causes the locked logic to 'de lock'

Renault and their instrument manufacturers were a pain when designing their instruments as they nearly always use 'application specific' IC's, which are very difficult to debug and almost impossible to get hold of.

Can anyone supply the instrument pod wiring diagram for this car, with that I might be able to suggest some noise filtering for the speedo that may prevent it getting into the locked state. Also and in the mentime there would be good value in ensuring that the speedo is getting a decent 13.2 volts by making sure that the earth and supply feed is good.

Just as aside, and not much good to you probably, if anyone has same problem on 5t or A310 then they should contact me as I can build you (at a price) a device that replaces the dodgy electronics of your speedo

[Alpineandy]

A310 then they should contact me as I can build you (at a price) a device that replaces the dodgy electronics of your speedo

The only problem I've had with the A310 speedos is that the needle sometimes warps and gets stuck on the view glass. I didn't think the speedo was dodgy electrics......

Whereas the rest of the electronics do look a bit 'iffy'.

My car always did the same thing - used to turn the ignition off and on quickly to make it work.

As I recall the problem has been identified as a specific component on the little circuit board located in the dash next to the speedo. It was in a Le Journal issue a few years back. Apparently easy to fix. I will try and get a pic of the board.

That was a diode on the PCB to the right of the rev counter, but some people have said it's nonsense.

Anyone have a definitive answer....... please! Or do we just have to point and laugh at TT drivers.

I loved the bit about the TT fuel gauge. At least it is a fuel gauge and doesn't use some crazy French logic based around fuel flow, the level originally in the tank and the number you first thought of.

An A310 wiring is fantastic in comparison to the 5T and an A110, so consider yourself lucky!

The A310 speedo can fail for the same reason as a 5T (version 1) as the drive electronics are the same. The application specific IC which is longer available fails. My fix replaces the electronics with new, using the original sender with the advantage that it can be calibrated for different front wheel rolling radius

[Alpineandy]

An A310 wiring is fantastic in comparison to an A110, so consider yourself lucky!

I consider myself lucky because I have an A110 and 2 A310s .
The A110s electronics appear basic and agricultural but hasn't been a problem (and I'm a poor mechanic and a truely cr4p auto electrician).
When something electronic doesn't work in an A110/310 check the earthing. If that doesn't fix it, call a professional

Well I've had my fair fill of speedo problems and found that squirting switch cleaning into the connector blocks works - at least it did until very recently

Now, after cranking the engine, it either flys up to 160 MPH or flips to around 28MPH or just lays at zero and doesnt work....

The only other thing I've noticed that might have something to do with this is the fact that the cold weather seems to have taken its toll on the battery as it feels a little hesitant on turning over - me seems to think if the voltage is dropping below a threshold on start up it plays the speedo circuit up causing these faults..

I'm putting the battery on charge this weekend so it will be interesting to see how it performs afterwards.

On my GTA the speedo will fly off to 160 when the battery is very low

[Alpineandy]

On my GTA the speedo will fly off to 160 when the battery is very low

When my battery is low I like to fly off.
Is this the sign of an alpine man