Fix temperature warning LED flickering - M-Body LeBaron 1979

69-

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The red LED in my temp gauge was flickering all the time. The sending unit and the gauge tested just fine.

It turned out that after 40 years the condenser on the little printed circuit right behind the gauge (not the big one!) was gone. It obviously dried out and had almost no capacity. It's the gray part on the lower left on the last pic.

Following procedure to replace it - as there are 2 transistors, be careful with static charges to not kill them:
- carefully remove Dash bezel (8 screws, 4 upper, 4 lower)
- remove 2 screws (right upper and left lower) of the Ammeter + Temp Gauge sub-cluster
- take this sub-assembly straight off (there's no more clips)
- carefully remove the 2 plastic clips to remove the cover of this sub-assembly
- remove 3 screws of the 2 gauges
- carefully remove temp gauge
- note polarity of condenser (the old one has arrows to PLUS! Nowadays, MINUS is shown on them), a photo with your smarty phone helps a lot. Cut wires of condenser short off printed circuit (leave a lead to solder a new one)
- carefully scrap clean the remaining wires (otherwise, soldering may fail)
- solder a new condenser with the same capacity (47uF, 50V is just fine) and obey the right polarity! (see above, take a picture)
- assembly in reverse order

LED goes on only, if coolant temp rises above a certain level (I tested only with my testing switch - with "full/hot" setting, it lights).

Be happy :)


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Ele115

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Mine does that in one of the police AHBs when the temp is normal. Has done it for years. I ignore it. That LED thing is useless
 

Mikes5thAve

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Now imagine something like this going bad on a car with newer electronics... I'd insert the crazy smiley here but don't want to wait for those to load to choose it...
 

Ele115

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You can't even do a burnt out brake light on the newer stuff. My highlander has LED taillights and I had to get the whole shebang when it went out. It was under warranty, but if it wasn't covered that would have cost me over $300 for a light thats out
 

Aspen500

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We see that at the shop every so often. Taillamp is out, or a portion of it doesn't light up, and then having to tell the customer it's going to be $200, $300, $500 to repair. Same goes for interior items like the HVAC controls, instrument cluster or radio. There is no practical way to repair them in the field. Only choice is go without illumination or replace with new or remanufactured assemblies, and some of those are not what you'd call inexpensive, especially f they require programming to the vehicle after installation. Then you have the (on average) $40 3-day subscription charge from the manufacturer to access the database and then download the data into the new cluster, or other module using a pass-thru device and laptop, then reset all the the customer preference parameters, and who knows what else.................Just so the darn thing lights up. I love my job, I love my job, I love my job, LOL.:p
 

69-

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You're buying way to expensive light bulbs :cool::p (just kidding)

And as you all said - that's the reason I'll switch my daily ride (currently a leased X5) to this LeBaron. I'll just fix it myself.
My last owned daily was a 2009 Phaeton - great ride, really, and all those gizmos on board! But let ONE cable go wrong - and NOTHING moves. Had that problem. And a rear light assembly is >300 USD - just the part. It'll take approx 1,5-2h to change it @100USD+/hour at your local dealership (did that myself while adding a trailer hitch to the car).

Anyway. I'll fix all I can at the LeBaron and have a really smooth, dependable and relaxed ride. :)
 

MoparDan

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Those are some of the reasons why I don't have a modern car: a $15. part for an M-body is a $300. part for a newer car, not to mention how many times I've Macgyver'd my way home when something(s) broke...can't do that on a car today :)
 

69-

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So true.

The Phaeton had to be pulled out of a tight parking space with all four wheels up... See enclosed...
DSC_2281.JPG
 

Aspen500

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Much easier to change a $2.00 light bulb.

Easier, sometimes. Ever see what it takes to change a headlight bulb or parking light bulb in a lot of newer vehicles? Step one, remove front bumper cover, pull back inner fender liners to access one of the headlamp assy bolts (in some cases), then remove the other 3 or so bolts from the front. Remove assy from vehicle. Then remove a cover on the back of the assy and finally, replace the friggin' bulb. Reverse procedure. Oh well, I guess that's what I get paid for, yes?:eek: Yeah I know, a headlight bulb is more than $2.00 but you get the idea. Maybe it's because I work on them all the time (newer vehicles, mainly 2007 and up now), they don't scare me. Of course, I own 3 vehicles, one is the '79 Aspen, then '96 Dakota and the newest is an '08 Mustang so don't really own a NEW car.
 

Cordoba1

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I agree that older iron is vastly, VASTLY easier to work on than the new stuff, but let's recognize what 69- had to go through to fix one LED, which would more-or-less be considered a non-serviceable item. 69, correct me if I"m wrong; but that looks like a 5 hour project -- and this assumes you knew what was wrong. $5 in parts... $500 in labor!

Great job and thank you for documenting!
 

69-

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You're welcome. That's what a forum is for, isn't it.

Pure labor was like 1h. The condenser was an educated guess, as old school transistors and resistors hardly give up (although, these transistors look like russian production, considering the special case...). And I have to admit, not the first dash being disected together with some good friend's IRC help.
All in, it probably took me less than 2h - with breaks.

I like to find out and fix (if I can). And seeing it being fixed is more rewarding than most things. Like you get THE new toy as a kid. :cool:
 

Cordoba1

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That's awesome! You're fast. I would take me an hour just to get to the part, let alone getting it on the bench with a soldering iron.
 

69-

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No no, it's quite easy. Just a couple screws. :D
 

Aspen500

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You're welcome. That's what a forum is for, isn't it.

Pure labor was like 1h. The condenser was an educated guess, as old school transistors and resistors hardly give up (although, these transistors look like russian production, considering the special case...). And I have to admit, not the first dash being disected together with some good friend's IRC help.
All in, it probably took me less than 2h - with breaks.

I like to find out and fix (if I can). And seeing it being fixed is more rewarding than most things. Like you get THE new toy as a kid. :cool:

That is big part of what this forum is for.

I always like to repair vs replace also (in certain cases), when possible. Even if I replace something, always end up tearing the old one apart trying to figure out what failed. The "I just gotta know" syndrome. Tough part with something like your gauge is coming up with the parts. Since Radio Shack went bye-bye a few years ago, on-line is about the only way to get a lot of electronic parts (at least around here). Or,,,,,,,,,,I can go raid my dad's basement. He has jars and jars (and jars, and jars......) of capacitors, transistors, resistors, tubes, diodes, etc. He was an electrical engineer until retiring a little over 20 years ago.
 

69-

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OK, I need to follow up on this one.

The new capacitor did fine the last 1.5 years. A couple days ago, the problem resurrected, unfortunately. Sometimes it did work as expected, and other days it didn't. Then, it was broke. The LED was lit all the time, the temp gauge worked flawlessly.

Re-examining the whole thing, nothing unusual detected. So, test the transistors - broke. :(

Checking for those types proved detectives detail-work. 2N5308 (a NPN-transistor) and a 2N5354 (it says GE5354, but - PNP transistor).
Not much information about those old types available. So, set up a circuit simulator, to find out how it works and being able to properly replace the transistors. It took me hours to find out, that both transistors are TO-98 case, but they have differnt pin layout.... :eek:
Replaced both correctly connected - and it works again.

Important information on this (found out with the circuit simulator): the circuit depends on the mechanical voltage regulator! If you replaced it with an electronic one (with straight 5V output for the gauges) it will not work, the LED will be lit all the time.
Difference is, that the mechanical regulator just switches 12V on/off like twice a second for 80 milliseconds. That is a big difference for the circuit - get a pulsed signal as input or a lower straight voltage...

I hope that this might be helpful for someone else

Here's the replacement transistors and the circuit in the simulation program.

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