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Old 09-14-2008, 03:53 PM
Registered User
Join Date: Aug 2008
Posts: 6
cleaning climate control circuit boards 124 300 tdt

I'm having no defrost and would like to clean the circuit boards which are
corroded. I have the back off the push button unit but would like some direction before I break it in disassembly.
Thanks, Ken

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Old 09-14-2008, 07:59 PM
toomany MBZ's Avatar
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Join Date: Nov 2006
Location: central Va
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You may want to check for cold solders too, not sure how to clean, why does it need it? Other than spraying the circuit board with a contact cleaner spray.
83 SD

84 CD
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Old 09-14-2008, 09:00 PM
compress ignite's Avatar
Drone aspiring to Serfdom
Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
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"Search" and "Advanced Search"

"Teach a kid to fish,and..."

"Plug-in" your search terms in the top left box of the "Advanced Search" subset...
I got this:
Intermittent cruise control
(Excellent tutelage on Soldering in the links!)
'84 300SD sold
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Old 09-14-2008, 09:58 PM
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
I have never personally experienced major corrosion on the traces of a circuit board. Or do not remember a pronounced case of it anyways. I suspect a soldering paste heated a little with a soldering gun might remove any copper oxide. After all its function is to clean the copper to promote solder adhesion normally. Never use acid type paste. Still this should be taken with a grain of salt. Others may have better ideals. Then there is the problem of removing any residue from the board after the proccedure. This part should be manageable.

The far more common problem was surface conduction through contamination. Sometimes hard to find initially on electronic boards. An alchol bath was recommended if caught early enough. Sometimes the board itself would develop leakage or resistance through the earlier phenetic type of material. I used to drill out the area where possible and jumper the area. This whole area was always questionable as there might be other areas of the board just starting to conduct as well.

I assumed this effect was caused by contaminated board material used in manufactuing. Or heat and aging made the board conductive. You might be better if the corrosion is really advanced to check out a junk yard unit. If those traces have major corrosion one could be open for example either before or after the corrosion removal.

At the least in severe corrosion cases I would suspect you might have to rebuild the copper traces with solder. Wait awhile as certain people on site do marine electronics and might have good suggestions. I am thinking people like Yellit who service marine radar units in the gulf area of the southern united states. The operational salt climate there has to be rough on units. You might want to drop him a note as I do not know how often he is on site. Good helpful guy if any possible solution is practical in my mind.
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Old 09-14-2008, 10:58 PM
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Join Date: Aug 2008
Posts: 6
Cleaning climate control circut boards

I think my question was unclear. How do I get the circuit boards out of the push button unit. I have cleaned the easily visible board. I cannot access the board for the fan switch etc. How do I remove the buttons etc.
Thanks, Ken
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Old 09-14-2008, 11:18 PM
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Join Date: Mar 2006
Location: Sonoma Wine Country
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The buttons pull off. Takes a good grip, pull straight out. May have to use pliers to grip them or a pair of screwdrivers to pry them off. Work carefully, they will pop off one at a time.

"Buster" in the '95

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Old 09-15-2008, 10:33 AM
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Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,767
Popping those buttons on the 124 CCU is tough. You want to pull the caps, not the white retainer (you'll see what I mean). If you pull the white retainer off of the end of the shafts, you risk about a 50/50 chance of breaking the retainers after which they will land in your center console whenever the button pops up.


Gone to the dark side

- Jeff
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