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#1
05-09-2012, 04:49 PM
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Rheostat?
77 300D
Problem is that the cluster lights are VERY dim. All the bulbs appear to be good. The other lights (heater, shifter) are at full strength. All lights respond well to the dimmer. I thought a rheostat failure meant no lights at all, but perhaps I thought wrong?
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New, Used & Rebuilt Parts for Classic Mercedes mbzparts.com 
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#2
05-09-2012, 05:40 PM
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The bulbs appear good because they light up or because you pulled them and looked at the glass?
Incandescent bulbs wear out before they burn out. As the filament glows, tungsten thrown off, some of this sticks to the inside of the glass. This silvers the inside of the glass reducing light output.
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#3
05-09-2012, 05:42 PM
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Your rheostat can be very dirty too
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#4
05-09-2012, 05:43 PM
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Pulled and looked at them. Didn't see anything wrong but I could look again.
Seems odd that all the bulbs on the dash would wear out together and the other ones would be find...
__________________
New, Used & Rebuilt Parts for Classic Mercedes mbzparts.com
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#5
05-09-2012, 07:33 PM
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The bulbs between the dash could be different, the others were changed . Is your dash the printed circuit type? I've seen the copper tarnish increasing resistance / lowering light output.
Put the bulbs against a white background or white light source then look through them, if they look silver / black / smoky, change them. Also sometimes you can get bulbs with a higher CP ( Candle Power ) that have the same shape .
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#6
05-09-2012, 07:43 PM
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Answer
Quote:
http://www.peachparts.com/shopforum/general-information/296474-w123-instrument-cluster-printed-circuit-board-repair.html .
__________________
ASE Master Mechanic https://whunter.carrd.co/ Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 2003 Volvo V70 https://www.boldegoist.com/
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#7
05-09-2012, 09:58 PM
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The prisms can get coated with film, too. I added some electrical contact enhancer to the bulbs, cleaned the glass, cleaned the prisms, put some reflective tape on the cluster. It all added up to a brighter cluster.
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#8
05-09-2012, 10:35 PM
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If they all went out at once, THAT is your rheostat assuming all your fuses are good. Pull the instrument cluster, get a can of electronic cleaner spray... radio shack ect... clean it and end your issues.
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1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#9
05-10-2012, 04:14 AM
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Rheostat Rebuild
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there were three HP ratings on the OM616... 1) Not much power 2) Even less power 3) Not nearly enough power!! 240D w/auto Anyone that thinks a 240D is slow drives too fast. 80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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