LS400 cluster not lighting up

Jack.pe · January 15, 2022

Hello all!

I have an LS400 with the backlights in the cluster not lighting up. All the dials work and all the smaller lights in the dash like indicators, gear selector, all work. However it’s the cathode tubes that don’t seem to light up. The needles flicker on for one second when the car is started and then go off and stay off. The car had a water leak from the windscreen for a long time so the cluster would have been subject to humidity but the board and contacts do not look corroded.
I found a scorch mark (pictured) on the board but the traces around it are still working.. so not sure how that happened.. also found one capacitor where the heat shrink had shrunk down indicating overheating so I replaced it (pic attached). Also found two resistors under the mosfet heat sink (mosfet and heat sink pictured) that looked overheated and replaced those too.
But still no lmprovement.
So it seems everything apart from the cathode tubes and needle lights is working.. but I’m not sure where to go from here any ideas or guidance on which components I should change next ? Is it the mosfet that feeds the cathode tubes? Should I try and change that?

I have been through about 20 second hand clusters on eBay and FB groups from 95-97 cars like mine but none are an exact match. There are so many variations so can’t just replace this cluster with a second hand one. Thank you 🙏

Malc · January 15, 2022

I have no idea how to advise you on your in-house repair issues ......... my dials sometimes "play-up" etc BUT earlier somewhere on here there's advice that a company called REM at Rochester Kent is a sound purveyor / repairer of our model clusters etc

I'm in Kent and propose visiting them sometime to have a chat about my issues .... when they can see first hand

You're in Oxfordshire so not so convenient BUT might be worth a call to them to discuss your options :unsure:

Malc

Howplum · January 15, 2022

My faulty instrument cluster was the bane of my life for most of last year, until I managed to source a replacement, although I did not have the same issues. Anyway, I have a couple of spare incomplete clusters and a full set of electrolytic capacitors which you might be able to use. My car is a 1996. It sounds like you are handy with a soldering iron, so PM me if you are interested. Incidentally, if you do end up replacing it, I found out how to retain the mileage.

Jack.pe · January 15, 2022

57 minutes ago, Howplum said:

My faulty instrument cluster was the bane of my life for most of last year, until I managed to source a replacement, although I did not have the same issues. Anyway, I have a couple of spare incomplete clusters and a full set of electrolytic capacitors which you might be able to use. My car is a 1996. It sounds like you are handy with a soldering iron, so PM me if you are interested. Incidentally, if you do end up replacing it, I found out how to retain the mileage.

Hey, yes I saw your excellent thread.. what a challenge!

I will PM you!

Malc · January 15, 2022

please let us know the continuing story and outcomes

Malc

Jack.pe · January 15, 2022

incidentally I have a YouTube channel and for background this video might be useful! another update specifically on the cluster coming soon,

The Water Leaks On My Cheap Lexus Are Much Worse Than I thought! (Luxobarge S2:EP3)

Razor61 · January 16, 2022

According to this https://lexus-europe.epc-data.com/ls400/ucf20r/5092/electric/8301/83291/ the ‘computer, combination meter’ for production period 10.1994 - 08.1996 may not work as the later versions are not listed as a substitute. For the remaining production periods they look to be interchangeable. I suppose the only way to proceed would be to find one from a car produced between 08.1996 - 07.1997 using the vin number.

I used epc-data to figure out if a later ECU would work which was listed as a substitute, I checked with Lexus and they confirmed it. So it’s pretty accurate with substitute bits.

steve2006 · January 17, 2022

Although for the earlier model this tutorial may prove useful in converting from cold cathode tubes to LED backlighting, it will obviously require a bit of detective work locating the required power supply for the LED strips but given your present level of electronic engineering competency should be do able.

http://www.lexls.com/tutorials/lighting/clustercolor.html

Linas.P · January 17, 2022

On 1/15/2022 at 10:03 AM, Jack.pe said:

Hello all!

I have an LS400 with the backlights in the cluster not lighting up. All the dials work and all the smaller lights in the dash like indicators, gear selector, all work. However it’s the cathode tubes that don’t seem to light up. The needles flicker on for one second when the car is started and then go off and stay off. The car had a water leak from the windscreen for a long time so the cluster would have been subject to humidity but the board and contacts do not look corroded.
I found a scorch mark (pictured) on the board but the traces around it are still working.. so not sure how that happened.. also found one capacitor where the heat shrink had shrunk down indicating overheating so I replaced it (pic attached). Also found two resistors under the mosfet heat sink (mosfet and heat sink pictured) that looked overheated and replaced those too.
But still no lmprovement.
So it seems everything apart from the cathode tubes and needle lights is working.. but I’m not sure where to go from here any ideas or guidance on which components I should change next ? Is it the mosfet that feeds the cathode tubes? Should I try and change that?

I have been through about 20 second hand clusters on eBay and FB groups from 95-97 cars like mine but none are an exact match. There are so many variations so can’t just replace this cluster with a second hand one. Thank you 🙏

Great content on your channel, I was wondering how long it is going to take to hear about Sumo on this forum 😄

Sadly can't help you much with the cluster, but hopefully you find the way to sort it out. The only comment I had on youtube was about wires which seems to be a little crusty, event thought (I assume) there is continuity, maybe they short to the board or to each other. I wasn't even convinced the burn mark was from trace on the board - if it would be trace it most likely be burned through. So my bet was on the wires causing the burn, perhaps replacing the wires or insulating them better could help?

Jack.pe · January 18, 2022

Thanks! I’ll make sure they are insulated but they shouldn’t short against the board as the part they were close to doesn’t conduct..

steve2006 · January 18, 2022

If they are the high voltage wires for the needles they could be arcing across hence why they light up for a second or 2 then go out.

I would separate the wires and as suggested apply some additional insulation to each one, PTFE tape is a good choice or a few layers of insulation tape.

I would also clean all those burn marks off the PCB as there could be arcing between the track and connector, a cotton bud and some isopropyl alcohol should do the job

Jack.pe · February 13, 2022

Got the spare dash kindly sent by HowPlum and swapped a few bits over but no luck. Trying to send to BBA Reman on Monday… see if they can fix the thing!!