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Am replacing Speedometer and Tachometer backlight CathodeTubes.
Was able to extract Meter Assembly following shop manual instructions.
However, there is little information on how to disassemble the unit so as to permit installation of the cathode tubes .
The white rear cover appears fastened to a circuit board from the inside, so am seeking input on best way to separate the circuit boards to gain access.
The rearmost circuit board appears vertically jumpered to the intermediate circuit board with molex style header pins..so what is the disassembly process?
Have worked on other Lexus clusters without encountering this issue.
Several images of the cathode backlight tubes.
Have an eye for backlighting..
Meter lacks uniformity and there appears several shaded areas - especially on the inner kilometers scale.
Worked on backlighting projects for Stewart-Warner and Motorola when once upon a time both companies were producing automotive instrument clusters...
Tachometer Cathode Tube Speedometer Cathode Tube Topside of Meter Backside of Meter Underside of Meter
Have you looked at Body Electrical, Combination Meter - Disassembly?
Here's the thing...
The illustrious Lexus Shop Manual provides that you simply remove 7 screws and it opens..
Wrong...and someone's going to ruin their cluster with these instructions
Here's the rub...they fail to mention a molex header strip.(not a flex cable, but a header strip) that jumpers between the circuit attached to the cover and the main board....
The shop manual is not instructive how this separates....
Here is how easy the shop manual presents disassembly of the back cover...this is incorrect. See next image. The header strip is shown in background. This must be seperated...
An access panel presents the top of the connectors...but what tool is used to release the header pins:
Access panel removed. What tool to use to release the header pins?
Modified my response to include an image with back panel access cover removed.
It depicts the male pins protruding through the female connector.
It would appear a special tool.is necessary to push them out in order to release the circuit board..
In any event, the shop manual.is, to put it mildly, incomplete..
Thank you that's a much better pic, can really see whats going on now.
I've seen these connectors before and they have always been friction fit on stuff I've worked on.
They can be a little stiff & crusty feeling coming apart and is easier to pull as straight out as possible.
I understand that you don't want to damage it by rough handling and like you say maybe it needs a special tool I would not want to tell you wrong.
Really looks like friction fit best I can see.
Your pic I am looking at.
Last edited by Margate330; Dec 15, 2021 at 09:17 PM.
Thank you that's a much better pic, can really see whats going on now.
I've seen these connectors before and they have always been friction fit on stuff I've worked on.
They can be a little stiff & crusty feeling coming apart and is easier to pull as straight out as possible.
I understand that you don't want to damage it by rough handling and like you say maybe it needs a special tool I would not want to tell you wrong.
Really looks like friction fit best I can see.
Your pic I am looking at.
Referring to the Meter section of the shop manual was raised...
The Author failed to include a critical initial step in procedural progression for separating the two circuit boards...and so as implied, it is not as simple as removing 7 fasteners depicted in sequential shop manual illustrations.
The access cover suggests some type of tool is required to accomplish this task and am pursuing this information.
Perhaps Toyota/Lexus issued a TSB or shop manual addendum...if anyone knows...
Visited Service Department at McGrath Lexus Chicago for input on best way to separate circuit boards.
It was suggested to use a fine pick to slightly move male header pins side to side in female compression connector.....and viola, separation.
After 23 years they were somewhat stuck.
Following Lexus Shop Manual instructions allowed disassembly of the cluster.
There are 16 dual purpose contact/retainer spring clips that hold gauges; fuel, tachometer, speedometer, water temperature to the cluster housing/flex circuit.
Removing these clips allows removal.of gauge face and access to circular Cathode Tubes.
Both tubes were slightly blackened, but not bad functioning for 23 years old.
Hopefully this resolves the splotchy backlighting and dim spots on the cluster face.
Will also change out some or most of the incandescent bulbs...doesn't make sense to replace those never on.
Back cover and circuit board separated from main board. Numerous electrolytic capacitors... Any input whether they should be repaced? Probably a good question to ask whether replacing any capacitors will erase mileage.. Majority are type "KME" ... United Chemicon??
Original tachometer cathode tube in cluster depicts blackening of tube - more noticable at uncoated tube ends. Replacement tube below.
Original speedometer cathode tube (top).depicts onset blackening. New tube below. Original Tachometer cathode tube (top). The pattern of heater(??).resembles Greek key inverse Meandre... Original speedometer cathode tube backside image above new tube. New cathode tubes installed in cluster housing...next is reassembly. Subject to availability, will replace 16 contact spring clips that retain water temperature, tachometer, speedometer and fuel gauges to the housing/flex circuit. 4 dual purpose spring clips per gauge serve as retainers/contacts between housing/copper flex circuit traces and gauge contact pins. Slight oxidation, so will replace all.
1998-2000 LS400 Instrument Cluster Meter uses Cathode Tubes for backlighting and incandescent bulbs in twist lock sockets for status fault indicators.
Am presenting the Japanese version because it provides clear labeling of bulbs and sockets for respective fault/staus indicators, while the North Ametican version is fair.
Tachometer and speedometer are reversed on right-hand drive, but bulb and sockets are correctly labeled.
This is what Lexus Dealers in North America are given to work with...
Hopefully this resolves the splotchy backlighting and dim spots on the cluster face.
Back cover and circuit board separated from main board. Numerous electrolytic capacitors... Any input whether they should be repaced? Probably a good question to ask whether replacing any capacitors will erase mileage.. Majority are type "KME" ... United Chemicon??
Great thread Yoda.
I would expect the car's milage must be stored in a non volatile EEPROM.
Below is a pic of some caps that act like backup batteries on a piece of
foreign equipment and they look different from other caps.
Only really used for keeping custom settings & parameters and real time clocks and stuff
like that but nothing as catastrophic as losing vehicle's mileage would ever be trusted
to a cap style backup battery because they can die and fail to hold charge
sometimes when they get old. Kinda like a rechargeable battery.
As far as cap replacements I always do a physical inspection and then a
"health check" with my ESR meter and change them as needed.
See the big fat caps in pic.
PS- looking forward to seeing pics of your work installed and all lit up when you get it done.
Last edited by Margate330; Dec 18, 2021 at 09:25 PM.
Back cover and circuit board separated from main board. Numerous electrolytic capacitors... Any input whether they should be repaced? Probably a good question to ask whether replacing any capacitors will erase mileage.. Majority are type "KME" ... United Chemicon??
Those capacitors are nothing to do with the stored mileage. The EEPROM holds it.
Regarding the type KME, those are standard 105℃ type conventional capacitors manufactured by Nippon Chemicon/United Chemicon in the late 90s and early this Century. Those are succeeded to KMG and do not contain the QAS liquid. They do not leak but evaporate in accordance with the Arrhenius equation. It will be a smart idea to use an ESR meter as Margate330 mentions and replace only poor ones. You can check most of electrolytic capacitors's ESR without removing them from the board.
Yoda, just for fun you feel like posting up pics of the chips on the circuit boards?
Maybe we can figure out if the mileage is stored in the cluster assembly if we see an EEPROM or if not it mostly likely the Engine ECU.
Also be cool to see what they are using to drive the circuitry if we can identify the chips.
Yoda, just for fun you feel like posting up pics of the chips on the circuit boards?
Maybe we can figure out if the mileage is stored in the cluster assembly if we see an EEPROM or if not it mostly likely the Engine ECU.
This is a good question cuz on my '93 I need to change my cluster with a rebuilt spare I have. Only problem is my car has 85K miles and my extra cluster, also from a '93, has around 185K so I'd like to change over the mileage some how. I'm not into electronics so I have no idea how, or if, this could be done. Sorry to jump the thread with different years.
Yoda, just for fun you feel like posting up pics of the chips on the circuit boards?
Maybe we can figure out if the mileage is stored in the cluster assembly if we see an EEPROM or if not it mostly likely the Engine ECU.
Also be cool to see what they are using to drive the circuitry if we can identify the chips.
The photo below shows my JDM 98 Celsior's main cluster board and the red arrow indicates the EEPROM for the odo meter.
The reason why I took this photo several years ago was to check how electrolytic capacitors were worn. The capacitor indicated by a blue arrow was not fully OK but still functioning. As you see the capacitor's top, the brown tube was shrinked too much. This must be affected by the heat from the heat sink used for the 5V regulator located to right next to it. The capacitor indicated by a green arrow also showed a bit higher ESR and smaller capacitance but this was still in OK range. With these results, I only have replaced the capacitor indicated by the blue arrow.
Need Input on 1998-2000 LS400 Cluster Disassembly
