Author Topic: Clock repair alternative to replacing solder fuse  (Read 198 times)

GM

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Clock repair alternative to replacing solder fuse
« on: October 17, 2020, 16:07:14 »
Hi all,
My project this week is repairing my clock.
I found this YouTube video that is a nice explanation of how/where to install a zener diode and capacitor in lieu of using the specialty solder fuse that is a common failure point for the clock, per the famous James Mahaffey article.
https://www.youtube.com/watch?v=zaoUMLz8vBc
I can add it to the Tech Manual if members want it included.
Gary
1971 280SL
180G Silver Gray Metallic
Black MB Tex

mrfatboy

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Re: Clock repair alternative to replacing solder fuse
« Reply #1 on: October 17, 2020, 17:44:13 »
Adding info to the tech manual is always a good idea👍
1969 280sl (Aug 1968 build)
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4 Speed

mbpaul

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Re: Clock repair alternative to replacing solder fuse
« Reply #2 on: October 17, 2020, 18:59:26 »
Here is an article on the MBCA website:

http://mbca.org/sites/default/files/7008874_Clockrepair2.jpg

It no longer includes the pictures but if you send me your email address, I can send you the entire document with the pictures, Word format.  The pictures are black and white and not the best but still give some good information. The procedure was written by James Mahaffey, a well known nuclear engineering expert from Georgia Tech, whose hobbies include these clocks and old Becker radios.

This article has some more information as well. 

http://www.benzworld.org/forums/r-c107-sl-slc-class/1545131-1972-vdo-kienzle-clock.html

In the youtube video referenced by GM, the person in the video calls the diode a "zener diode" but it really just a plain old diode.  Amazon has the 1N4002 for but you may have to buy them in packs of 5 or 10.  Most any diode will work.

My clock had not worked in about 30 years and this mod was all it took to get it going again.

GM

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Re: Clock repair alternative to replacing solder fuse
« Reply #3 on: October 18, 2020, 16:26:55 »
Thanks, mbpaul for your help. Apparently I missed your earlier post of that video.

Well, the clock repair didn't exactly go as planned. After opening the back, I discovered what looked like a "mini explosion" happened, which resulted in a large area of black soot and pieces of who knows what on the inside of the plastic cover.
Not only was the solder fuse connection melted, as expected, but whatever happened also resulted in a resistor badly overheating and partially melting some of the teeth on a lower gear. Oh, and the over heating also partially melted the main solenoid coil and its core, which is now coming out of the bottom of the coil.

Any speculation on what might have happened?

On to finding a good reasonable repair shop, and the dilemma - to restore or go quartz?
Gary
1971 280SL
180G Silver Gray Metallic
Black MB Tex

mbpaul

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Re: Clock repair alternative to replacing solder fuse
« Reply #4 on: October 18, 2020, 16:54:56 »
Have no idea what might have happened.  I suspect I would try to find a quartz version.  Plenty on ebay along with some of the kind you have.  And the prices seem reasonable.

There are some places selling new clocks in the $400 to $500 range.  I suspect I would take the risk that goes with ebay.