Intermittent instrument cluster

[Omega man 1969]

I have an issue with my instrument cluster where the dials will drop to zero and then come back to life from time to time. I have checked the power on pins 15,21 and 23 of the 26 pin at the rear of the cluster and it all checks out ok.
With DIS connected I can see that it thinks terminal 15 (pin14 of the cluster) doesn't have supply voltage. This leads me to the conclusion there must be a dry joint in the cluster itself. I have checked everything I can on one side of the cluster PCB but can't figure out how to remove the PCB from its plastic backing. Has anyone here been successful in removing the PCB?

[revtor]

The PCB is mounted with plastic heat stakes. The only way in is destructive: Drill or cut off the heat stake heads. Don't worry too much about the fact that you can't secure the PCB anymore on the decapitated stakes. When the unit is reassembled the PCB is sandwiched between both halves of the instrument cluster and can't go anywhere...

Don't forget to take off the trip/odometer unit first (depress tab and slide unit down).

[Omega man 1969]

Thanks Revtor, I thought you would know :-)

How about a DME with fuel trims that are stuck at zero ? All inputs read good , temp, Lambda etc. I’m thinking DME RAM failure .

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When you say heat steaks , do you mean the 5 plastic pins sticking up? Do they just snap off ?

[revtor]

No no! Don't remove those pins!

Carefully look over the PCB and you'll find 7 plastic rivets that secure the PCB to the enclosure. These are the heat stake heads.

About the DME mixture adaptations stuck at zero... Although it is theoretically possible zero values are the proper adaptation values for that module, chances are small. The adaptions are lost on battery disconnect or removal. Are you sure you did not remove the DME very recently? Are the adaptation values still zero after you let the engine run for some time or took the car for a short drive (diagnose with the engine still running - maybe a wiring issue cuts power to the DME when switching off the ignition)?

[Omega man 1969]

No no! Don't remove those pins!

Carefully look over the PCB and you'll find 7 plastic rivets that secure the PCB to the enclosure. These are the heat stake heads.

About the DME mixture adaptations stuck at zero... Although it is theoretically possible zero values are the proper adaptation values for that module, chances are small. The adaptions are lost on battery disconnect or removal. Are you sure you did not remove the DME very recently? Are the adaptation values still zero after you let the engine run for some time or took the car for a short drive (diagnose with the engine still running - maybe a wiring issue cuts power to the DME when switching off the ignition)?

OK I will take a look for the plastic rivets, thanks.

I did disconnect both DME's then let the car warm up, the other DME was adjusting fuel trim short and long term. Both had the same engine temp value along with load, ignition timing etc. I could see that closed loop was on so that rules out failing o2 sensor, that was my first suspicion. I will swap the DMEs around and see if the fault moves.

[Omega man 1969]

Can't see any rivets...can you point one out please.


Ah I think I see them.....there is one either side of the catch at the top of the PCB, just where the lacquer ends . 8 in total .

[revtor]

All heat stake locations. I remember only seven, though. Where do you see an eight one?


Click for larger

[Omega man 1969]

You’re right, only 7. Also you have to stick two small pins down the back of the cable connector as it also locks the pcb against the plastic backing . I managed to free the PCB and will see if I can find the problem .

on the DME issue, I swapped them and the fault moved with the DME, it also shows an error code “DME control unit 333”

[Omega man 1969]

I checked the capacitors on the instrument cluster today, they all checked out good as do all the other components that I can get to. I think the next step is to try a used cluster. Gave the car a much needed clean today .

[850Freek]

I am having a issue with my cluster where the lcd does not display anything and the four gauges (Fuel, Tach, speed, temp) do not work. But they all work if i do the self test by holding the reset button. I also notice that the 2 light bulbs behind the lcd turn on very dim. Does this mean a short on the board? Any help would be greatly appreciated.

I replaced the 3 capacitors and the cluster was working but was going off and on until it just does not come back on.