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I don't seem to be getting anywhere finding a replacement cluster so am investigating replacement of the relevant electrolytic capacitors, which I assume are the the cause of he misbehaving fuel and temperature gauges. I've read about there being three capacitors which can cause issues, the third being for the panel lights (which work just fine).

Anyway, I was a bit surprised to find that there are 12 capacitors in total with very little commonality between them. On visual inspection they all look fine, but that probably means nothing.

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I have done a sketch of the capacitors and their details and wonder if someone would be kind enough to tell me which ones I should be ordering.

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I'm not sure my soldering skills are up to replacing the very small ones, so the next step is finding someone to test/replace the suspects.

Any help would be greatly appreciated.

 

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Whilst there is nothing obviously wrong on the side with the larger components on it, the other side is a different story, which is no doubt a result of the historic damp issues. All of the solder joints are suffering from surface corrosion, which hopefully will clean off with contact cleaner. However, in the following picture the corrosion on the solder joint to the left of C126, which is the positive connection to capacitor C132 on the other side, appears to be spreading, potentially onto part of the circuit it shouldn't.

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Here's another picture showing corrosion on the many smaller components:

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It looks like I need to be busy with the contact cleaner, fibreglass pencil and magnifying glass. Who knows, I might get lucky.

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Well, cleaning up the rear of the PCB made it look better, but unfortunately didn't cure the problems, so I now throw myself at the mercy of any electronic experts who might be reading this.

I did speak to BBA-Reman this morning, who said a repair would cost in the region of £175, which I'm a bit reluctant to shell out for at the moment.

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The fuel gauge always shows empty with the low fuel warning light showing on the first start of the day, although on a subsequent starts it usually shows the correct level, with no warning light. However, I did notice last year that on a longish journey the needle would slowly drag itself to the correct position, but that could take anywhere between 30 minutes to an hour.

The temperature gauge only ever moves a few millimetres from it rest position, not even reaching the lowest mark. However, I did dismantle the entire cluster last year in an attempt to sort out some non-functioning lights (which @steve2006 kindly sorted out for me in the end), but I wonder if I accidentally damaged the gauge in some way.

All other functions of the cluster work normally so it makes sense to repair my existing unit rather than try and source a used one, which might have its own issues. At least swapping the odometer is simple enough.

Any advice you can offer would be appreciated.

 

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Easiest way to determine if it’s the cluster or sender unit is to remove the connection to the sender on the tank and ground it...this should produce a full tank indication on the cluster. If it doesn’t you either have a broken wire between the sender and cluster or a faulty cluster.

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Not impressed with their electronics maker. Any such circuit should have been sprayed with a conformal coating AFTER the circuit was soldered and that pretty obviously hasn't or there would be no corrosion on those contacts. Mind you it's been good enough for 20+ years and Lexus really don't care after 10 years.

You can reflow those solder joints with a soldering iron, but you need to be aware of what you are reflowing and what effect the heat of the soldering iron might have. Electrolytic capacitors do not always look visually damaged when they die and the only real way to test them is to remove them and use a capacitance meter on them.

As Steve said, I would eliminate all other possible causes, and once certain the problem is in the instruments, send them off to be done by a pro.
Messing with electronics you can sometimes cause more damage than you fix, especially if there are CMOS integrated circuits in there as they are very sensitive.

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Thank you Steve and George for your replies.

As far as the fuel gauge is concerned I am assuming, possibly incorrectly, that the sender is OK since the it works fine once the car has been running for a little while, even just on a local trip to the shop. Nevertheless, I will test it as suggested.

On the other hand, the temperature gauge is consistently misreading, so it might well be that the sender is faulty.  I see from the wiring diagram there are two wires, brown and red/blue. I have just watched a video testing a sensor in situ with a multimeter which looks straightforward enough.

In layman's terms, what is the function of an electrolytic capacitor?

Do faulty capacitors tend to give consistent symptoms?

I do have a spare cluster, albeit from a 1997 model, but perhaps the gauges themselves could be swapped, if other tests prove inconclusive.

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I'm assuming the coolant sensor, of which there appears to be only one, sends a signal to the instrument cluster, either separately or  via the ECU. As far as I am aware I have no running issues, which seems to be a symptom of a failing sensor.

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16 hours ago, Howplum said:

I'm assuming the coolant sensor, of which there appears to be only one, sends a signal to the instrument cluster, either separately or  via the ECU. As far as I am aware I have no running issues, which seems to be a symptom of a failing sensor.

 

16 hours ago, Howplum said:

Thank you Steve and George for your replies.

As far as the fuel gauge is concerned I am assuming, possibly incorrectly, that the sender is OK since the it works fine once the car has been running for a little while, even just on a local trip to the shop. Nevertheless, I will test it as suggested.

On the other hand, the temperature gauge is consistently misreading, so it might well be that the sender is faulty.  I see from the wiring diagram there are two wires, brown and red/blue. I have just watched a video testing a sensor in situ with a multimeter which looks straightforward enough.

In layman's terms, what is the function of an electrolytic capacitor?

Do faulty capacitors tend to give consistent symptoms?

I do have a spare cluster, albeit from a 1997 model, but perhaps the gauges themselves could be swapped, if other tests prove inconclusive.

A capacitor is basically a reservoir of power that enables a constant supply through surge and drain episodes it is also used for shunting components such as electric motors that are induction motors  which need a power boost to start rotating.

If a capacitor is failing symptoms that you are describing do occur but are not limited to a faulty capacitor.

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I find all this electronic mullarkey starting to go awry so so frustrating  .........  we have fabulous cars, comfy, powerful and purring like a pussycat and we can relatively easily achieve component continuation ..  e.g UCAs etc ................... BUT the quarter century old electronics seem to be not quite so well at " holding up " and very tricky to resolve

Can't for one moment imagine that a quarter century young new, modern EV will be any better tho .................  and probably just simply a throwaway :wink3:

Malc

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1 hour ago, Malc said:

BUT the quarter century old electronics seem to be not quite so well at " holding up " and very tricky to resolve

I suspect almost any car over a certain age will have electrical gremlins, which is why forums such as this, and enthusiasts in general, help keep our cars on the road, despite the lack of support from most manufacturers.

At least Lexus didn't use bio-degradable wiring for the engine harness, which is what Mercedes-Benz did in the 1990s.

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