Fuel and temp gauges dropping out

[hiy_po]

Does anyone have a wiring diagram for a VK Berlina dash? I have the diagrams that show EST and EFI and complete car but they all seem to stop at the dash.
My gauges all seem to work fine when I first start the car but after driving for about 15mins they both drop down to zero until the car cools again. I want to look a schematic to see if the two gauges share an earth or something that may not be connecting.
It has only started happening the last couple of weeks and because I have to do a bit of travelling soon I would like the fuel gauge to work continuusly. Has anyone else had this prob and solved it? what did you find wrong?

[VK SL 3800]

The whole dash shares the same earth im pretty sure, does the oil pressure gauge also go crazy? I have a tacho dash circuit board somewhere, ill have a look what connects to what.

[hiy_po]

No all the other gauges and backlights work fine all the time. The problem seems to only effect the working of the 2 gauges and they seem to fail or work together so I am looking for something common to both.

[vkberlina]

I have diagrams on my site, my money is on earthing

scott

[hiy_po]

I can only see the diagrams that I already have. Can you post the url to the dash schematic? Yer I would guess it is an earth but an actual schematic of the dash would really help to try identify and test for it. I am thinking the gauges share an earth but I also think the gauges share a positive and the fuel earths threw the variable resistor that is the sender unit and the temp gauge earths threw a thermal resistor in the temperature sender unit so could be a positive supply prob as well. A schematic would really help.

[drewVHSS]

I can only see the diagrams that I already have. Can you post the url to the dash schematic? Yer I would guess it is an earth but an actual schematic of the dash would really help to try identify and test for it. I am thinking the gauges share an earth but I also think the gauges share a positive and the fuel earths threw the variable resistor that is the sender unit and the temp gauge earths threw a thermal resistor in the temperature sender unit so could be a positive supply prob as well. A schematic would really help.

Correct, all the gauges are fed positive from the ign source. each sender earth's out to give the required signal to the gauge.
If after warming up you still have power on the positive side of each gauge, then you have an issue with an earth being shorted between the fuel gauge and the temp gauge.
These clusters are getting on a bit and i wouldn't be suprised if the voltage regulator on the cluster is on it's way out or you may have a dry solder joint.

[VK SL 3800]

Im looking at a cluster in front of me, those particular gauges share a common power wire not connected to anything else, it (12v ignition) comes in through a little cube (some sort of transistor i think) which has three legs, 12v ignition, resistor to earth (9.6 ohms) and out to temp and fuel gauges. Either the resistor or transistor are faulty is my guess.

Must run a different voltage to promote smooth operation without fluctuations like the volts and oil pressure gauges.

[hiy_po]

OK I found the specs on the voltage regulator

TCA700Y
Fixed Positive Voltage Regulator
Various
Positive Voltage Regulators
Output Voltage Nominal (V)=10
Load Current Max. (A)=220m
Supply Voltage Maximum (V)=16
Package=SIP-tab
Pins=3
Military=N

It looks to be the most likely cause, and they are now obsolete new. I do have a spare so will plug it in and see if it fixes the prob.
I made a little and very basic diagram of the circuit if anyone finds it useful

[TY318]

hmm kinda sounds the same as my oil gauge on my vh all my oil gauge dose is go straight to the other side of the gauge lol and stays there but sometime once its warm i can sit at a set of lights and the gauge will randomly work lol then i rev it and it just goes off the gauge again lol and also that with a new gauge and oil sensor

[VK SL 3800]

You have a broken wire somewhere between the gauge and sensor, an open circuit sends the gauge to max.

[TY318]

You have a broken wire somewhere between the gauge and sensor, an open circuit sends the gauge to max.

would it matter if the wirer is to big

[hiy_po]

I dont see how a wire can be too big? A wire can be too small, or do you mean your connectors are too big and a loose fit. That would most definatly be a possible cause of an open circuit that would sometimes work and sometimes not.

[TY318]

I dont see how a wire can be too big? A wire can be too small, or do you mean your connectors are too big and a loose fit. That would most definatly be a possible cause of an open circuit that would sometimes work and sometimes not.

sorry i ment to think connections r tight