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  #1  
Old 03-16-2009, 05:55 PM
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'86 560SL clock problem - replaced capacitors, but???

I just replaced the capacitors in my clock and I still have the thing on my bench, hooked up to 12 volts. I have power - the wheel is moving, but it is not rotating - it jumps back and forth, from one side to the other and as a result, of course, the hands are not rotating, nor are any of the plastic 'gears'...

Can you install these capacitors backwards - is this an electrical issue or a mechanical one - something binding?? I can't SEE anything, but I'm not a clock expert!

Clock was working fine and then just quit...

ryan

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1984 300D
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1986 560SL
1991 300CE
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  #2  
Old 03-16-2009, 06:47 PM
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Those capacitors are electrolytic and are polarized so you must install them correctly. The originals may have had a small + sign on the positive side or may have had a stripe on the negative side. Replacements should be the same capacitance in microfarads and a voltage rating at least that of the originals.
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  #3  
Old 03-16-2009, 08:15 PM
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OK, I'm pretty sure I installed them correctly - and I used radio shack 100uF, 35WVDC, part number 272-1028 (which got from the archives). I'm going to to do it again and double check - but it almost looks like there isn't enough juice. Kind of like what a battery operated clock will do when the battery gets low...

ryan
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1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 03-16-2009, 11:32 PM
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If the clock is working properly, it will work fine on a 9 volt battery (it will probably be killed by reverse polarity, so be careful!). I have a spare mechanism that I repaired earlier, and I just tried this.

Are the gears reasonably clean? This thing has very, very little power to work with. If not, I might try a little silicone spray and a Q-tip on them. DO NOT USE OIL OF ANY KIND, period.

Are all the gears straight up and down? I had a mechanism that I could not repair with a broken pin on the end of one of the gear shafts.

There is a - sign on the back of the PCB where the - stripe on the capacitor should line up at. It's small and you might need a magnifying glass to see it. Note that this is different than (at least US) convention, where + is marked.

Did they give you TWO of each? it isn't unheard of for RS stuff to be DOA. I'd try again, being careful not to overheat the board and lift the traces. This is not a modern board and it will not tolerate a lot of heat.
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  #5  
Old 03-16-2009, 11:47 PM
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Strife,

Thanks for the reply. I just got done a little bit ago and currently the clock is working great. I believe that I had one of 2 things happen - a bad capacitor from RS, or I did get things too hot and shorted out some of the trace lines with too much solder. I think I ended up connecting a few lines that I shouldn't have...with excess solder. I went back to RS and bought 2 new capacitors and installed them, so I think I had one bad capacitor.

I know this - I definitely got the board too hot and did lift some of the solder lines from the board! I tried to fix them as best I could and on my last repair attempt, I clearly had a broken solder line. As best as I could, I got the line connected with some new solder and currently the clock has been keeping time for the last 90 minutes or so. I had trouble with the simplest things - like cutting off the excess capacitor wires after soldering - this caused a line to break and I had to do some more soldering...

I did figure out how to check the resistance/continuity of the circuit board lines with my analog meter. I think everything is put back together pretty solid, but I am going to look for another clock! Do you think using too much heat and lifting some of the trace lines is going to cause me trouble down the road?

ryan
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1984 300D
1972 250
1986 560SL
1991 300CE
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  #6  
Old 03-17-2009, 12:49 AM
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A good, but ugly way to replace a broken trace is to remove what's left of it and replace it with a cut-off lead from a resistor. If the whole thing isn't actually lifted off but just broken or lifted in the middle, you use the cut-off resistor lead to bridge the two pieces and solder it to the traces. This, for example, is what I did with my repair on the infamous blown trace on the back of the later electronic speedometers.

Using solder alone to bridge something is not a good idea, because it's brittle on its own and won't take a lot of vibration or flexing.

Well, I wouldn't put it on the Space Shuttle, but as long as the traces are not actually floating way above the board (where they will vibrate and break), I'd push the trace down flat against the board and tack it down with (a very little bit of) Superglue.
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85 380SL
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http://juliepalooza.8m.com/sl/mercedes.htm
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  #7  
Old 03-17-2009, 04:32 PM
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I got everything back together and clock works fine - but my tach doesn't work now! I had to pry the needle off and then press it back on and I guess I must have used too much force pushing the needle back on the post. Took the car for a drive and the gauge read 1300 rpms - period. Turned the car off and the needle stayed at 1300 rpm's.

I pushed the needle on with some force - if I didn't then the needle would flop around. Any ideas?

Ryan
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1984 300D
1972 250
1986 560SL
1991 300CE
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  #8  
Old 03-18-2009, 12:17 AM
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Did the needle spin free when you replaced it?

Is the needle bent and rubbing on the gauge face?

The only other thing I can think of is that the shaft is off of the bearing on the back of the tachometer, and I've never gotten that far into it.

The good news is that spare tachs are not nearly as expensive as spare speedometers (although you may not get one cheap with the redline that you want).

Why did you remove the needle?
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With homebrew first gear start!
85 380SL
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http://juliepalooza.8m.com/sl/mercedes.htm
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  #9  
Old 03-18-2009, 12:31 AM
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Popping the needle off made removing the clock mechanism much easier - it got the face out of the way.

The needle did not spin freely, mostly because I pushed it on harder to keep it from dropping down (counterclockwise) into the clock area.

The needle pops off - with some force - using a screwdriver, and it just pushes back on. I don't really understand how the tach works - maybe the needle isn't supposed to be pushed down as far as I tried to push it.

I can't see it binding anywhere...maybe from the rear (I could have bent something pushing the needle back on).

Ryan

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1984 300D
1972 250
1986 560SL
1991 300CE
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