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  #1  
Old 09-06-2005, 07:44 PM
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Tach Amp Question?

Anyone know how to take the tach amp apart? Mine is still being very flakey & I'm thinking that maybe some solder connections are coming loose like the ACC & Cruise modules. I looked at it a while ago & didn't see how to do it.

Thanks!

Mike

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  #2  
Old 09-06-2005, 11:48 PM
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Quote:
Originally Posted by McRoth
Anyone know how to take the tach amp apart? Mine is still being very flakey & I'm thinking that maybe some solder connections are coming loose like the ACC & Cruise modules. I looked at it a while ago & didn't see how to do it.

Thanks!

Mike
its potted in a silicone glop...not easy to remove or redo afterwards..
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  #3  
Old 09-07-2005, 12:46 PM
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Mike,
Let it go. Everyone on this board will tell you they don't work except for a few individuals who have been smiled upon by some supreme being. You want something else that never worked? Try the cool removable combo glove box light/flash light in the first 450SLs.

Peter
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  #4  
Old 09-07-2005, 01:06 PM
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I screwed with that stupid thing 2 dozen times over the years, for about a 2% success rate (total). The last time, I actually had some success. Instead of foam under the cap, I used a wavy washer. Then, I crimped the sides of the pins (careful, I cracked part of one off) to try to get the pins to contact better. Now, it works 80% of the time, maybe more. Don't get your hopes up though. It's been 2 months now, but I'm still waiting for the other shoe. BTDT.
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  #5  
Old 09-07-2005, 02:06 PM
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Quote:
Originally Posted by boneheaddoctor
its potted in a silicone glop...not easy to remove or redo afterwards..

once you have it off just melt your fav. color crayon on the top of the board.
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  #6  
Old 09-07-2005, 02:52 PM
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remove the silicone carefully.i admit a rather tedious process.there you will find a small circuit board.examine this carefully with a high power magnifier and resolder any suspect joints.test it and if alls well reapply some silicone and congratulate yourself on solving one of the most irritating small problems that we MB owners face
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  #7  
Old 09-07-2005, 03:39 PM
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Quote:
Originally Posted by michael cole
remove the silicone carefully.i admit a rather tedious process.there you will find a small circuit board.examine this carefully with a high power magnifier and resolder any suspect joints.test it and if alls well reapply some silicone and congratulate yourself on solving one of the most irritating small problems that we MB owners face

It worked for me. Remove silicone you will find corcuit board. resolder alljoints. Se if work .apply silicone.
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  #8  
Old 09-07-2005, 03:53 PM
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Quote:
Originally Posted by 83sdturbonut
It worked for me. Remove silicone you will find corcuit board. resolder alljoints. Se if work .apply silicone.
You can't use just any silicone....most weep acid when they cure....acid and electronics don't get along well with each other.
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  #9  
Old 09-07-2005, 03:55 PM
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Quote:
Originally Posted by michael cole
remove the silicone carefully.i admit a rather tedious process.there you will find a small circuit board.examine this carefully with a high power magnifier and resolder any suspect joints.test it and if alls well reapply some silicone and congratulate yourself on solving one of the most irritating small problems that we MB owners face
I found removing that silicone somewhat akin to cutting a tall, thin piece of tapioca pudding.
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  #10  
Old 09-07-2005, 04:05 PM
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I wonder what it woud entail to design and make a 'replacement' amp?

In my infinite wisdom, I reefed down on the cap one day to restore the tach to wholeness and managed to break my circuit board in two. I think that if I could ever figure out what components it took, I'd breadboard an amp and hard-wire it into place.
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  #11  
Old 09-07-2005, 04:11 PM
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You would be the hero of a lot of people here if you figured that out...I have not heard of any schematics of that assembly....nor have I tried to reverse engineer one yet...I do have a dead one, all I need it time.....maybe this winter.. as long as there are no house labled components... or special ones (fairly doubtful on the old stuff)
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1971 280SE W108
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1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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  #12  
Old 09-07-2005, 04:27 PM
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I really tried to figure it out a while back. That stupid silicone really stopped me. If anyone ever makes an alternative, I'll bite. They want a lot for the same dumb thing that doesn't last.
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  #13  
Old 09-08-2005, 07:48 PM
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Wow, finally checked back in on this thread & I guess I hit a nerve! Darn thing! I'll probably try to take it apart one of these days & resolder it then. Just buggs the CR** out of me!

Thanks for all the tips/replies!
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1982 300TDT Wagon
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  #14  
Old 09-08-2005, 10:32 PM
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Yep I agree

the tachs seem to be possessed but if you figure this thing out please post a reply...Mine jumps up and down and dances a jig on a regular basis...
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  #15  
Old 09-09-2005, 07:50 PM
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Long walk through dense forest - anybody up for it ?

I too have a suspect tach amp - I've been trying to mount a tach in my 240D (more news later...)

I took it apart, and took a dremel wire brush to the silicone goop - there is a LOT of that stuff- but the wire wheel (stainless) seemed to whisk/melt it away without doing TOO much damage

I made a pencil drawing of the botton of the circuitboard, wire colors are mapped out, I could post this stuff up BUT:

1) I accidently wirewheeled off the markings on a big capacitor - no longer readable

2) There is a 14 pin DIP (microchip thingie) in the middle of the board - I dont think it had any markings on it when it was put on - I left the top untouched so I didnt remove any more markings - but I cant find any. Some of the pins are unused, but that doesnt make it any easier (unless we have some **serious** EE power on this board.

3) most of the rest of the components are simple resistors or diodes - It'd be tough to read the values on everything else but could **probably** be done = more than I cared to do last night.

I'm not sure how many 14 pin DIPs there were in 1970-something (when this was designed ?) but unless someone on the board thinks that they could piece together the DIP and the capacitor (or dremel apart thier own tach amp and hope it is marked better) I'm not inclined to continue my quest - any thoughts ?


(I may have big news for 240D owners that want a tach though- it looks like the pickup from a 300D should fit - I've yet to test - I'll put results in the 240D tachometer thread when I get them...)

Does anyone want to walk with me on this tach amp thing ? I dont have a digicam (seeing the size of things might help) but I can steal my brother's if I need to.

-John

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