Analog Clock In Dash Not Working...

[longston]

My clock used to work great. Then I replaced the old battery in my '82 W126, and since then it stopped working. The fuses all check out in the fuse box under the hood, so is there another one somewhere? I'd like to have my clock back.

[Ron Johnstone]

This site has a great article on how to repair clocks. I need to do it also, but just need the time (no pun intended)
http://hsb.baylor.edu/html/easley/autofaqs/clock.htm

Scott,
Repairing the clock is fairly simple. Remove instrument cluster. Remove tach&clock assembly. Gently pry clock hands off. Leave tach hand in place. When you get the clock works out you will see two electrolitic capacitors. One of them is probably bad, but go ahead and replace both of them. They cost $1.00/each at Radio Shack.The original ones are rated at 16 volts; the new ones at 35VDC. The size is 100uF. Radio shack part No.272-1028. I repaired the clock on my 1983 300SD last fall.Works fine. I also fixed the glow plug relay by replacing a capacitor. Same size as the one in the clock. Seems as though the 16 volt rating is not high enough. A fully charged battery at optimum temp. is 13.2 volts. Not a lot of leeway there.
Bill Lewallen Lexington,Ky. Where diesels purr and turbos whirr and our cars are full of the Green coolant.

[Palangi]

It's a minor point, but proper circuit design is to select an electrolytic capacitor rated about 20% higher than the applied voltage. In this case, being a very low demand situation, it won't really matter much though. It would certainly outlast the remaining life of the car itself.

Paul,
For some reason the capacitors rated at 16 volts will not last the life of a Mercedes. I would prefer replacing it with one rated at 35 Volts. And they are the same physical size. I have replaced dozens of them, and they are all working just fine.
Bill Lewallen Lexington,Ky. Where diesels purr and turbos whirr and our cars are filled with the Green coolant.

[Robert W. Roe]

Yeah, I see 14 volts all the time on my SD. 2 volts isn't much reserve for power surges, jump starts, chargers, etc. I thought as far as working voltage, as long as you don't go too low, you are ok. In other words, 100 or 35 volts would be fine for a 14 volt application. As long as you don't reverse the leads on a polarized electrolytic

[Palangi]

Bill, It's not a matter of conservative rating. Electrolytic capacitors eventually die of old age. The closer they are run to their rated voltage during their lifetime, the longer they last. When we are talking about low voltage at very low current like in this clock circuit, we are basically talking shelf life of the component. It will most likely go bad in x number of years whether it is in a Mercedes clock, or sitting on the shelf at Radio Shack.
If you want to experience the thrill of a really bad electrolytic capacitor, if you go dig up some old tube-type radio that has been in the attic since the 50's, it will probably have some paper electrolytics in the 150 to 250 volt neighborhood. There is a good chance when you power up an old radio like that, there will be a nice BANG, accompanied by paper and tinfoil confetti. Pretty neat entertainment!
Cheers

Palangi,
The 16v rated capicators in MBs are only 2.8v over the battery voltage. If a capacitor should have a working voltage of 20% more than the circut voltage,and with a fully charged battery of 13.2 volts, that would call for a capacitor with a working voltage of 15.84volts. Thats getting close to the rated voltage of 16v. It's a wonder they last as long as they do. All the ones I have replaced have been rated at 35WVDC maximum. I didn't ask, but I doubt if Radio Shack has any 100uF electrolytic capacitors rated at 16WVDC.
Bill Lewallen Lexington,Ky.Where diesels purr and turbos whirr, and we fill our cars with Green coolant.

[Palangi]

Actually, this is one of the little things that needs fixing on mine also. One of these days when I have some spare time I need to get a handfull of bulbs, some tuner wash and a couple capacitors, pull the cluster and take care of everything back there. I suspect the clock has been replaced on mine before I bought it. The clock hands are still a bit orange, all the other hands are pretty much yellow.

[longston]

I've let this thread go in the hopes that someone eventually would say that there was an in-line fuse on the back of the clock, or something like that. But then, everytime my door bell rings, I keep hoping it will be Ed McMahon standing there with a huge checque for me.

Oh well, I'm no stranger to my Unger soldering iron, so I'll get around to it in the near future, just like I fixed my tach sending unit by soldering on it a couple of months ago.

Thanks to everyone for their help, especially my friend, Bill, I put in green coolant for St. Patty's Day, Lewallen...

Scott,
Bless you. I hope you get your clock fixed in time for St. Patricks Day. I'm like you in a way; I like for the clock in my car to work. All three of mine work, and they keep very accurate time. Had to fix two of them.
Bill Lewallen Lexington,Ky. Where diesels purr and turbos whirr and we put The Green antifreeze in our radiators.

[jcyuhn]

I actually performed this surgery on my '87 300TD within
the last few months. The clock hadn't worked since I
purchased it a year prior.

Upon removal, I found that the single resistor on the
circuit board was burned up as well - ugly black carbon
and all. Digging out my handy multi-meter, it appeared
to be about 150ohms (could not read the color bands on
it - they were ruined by the overheating.) One more trip
to Radidio Shack, and we were back in business.

Amazingly enough, after replacing both capcitors and the
resistor, the dang thing worked, and keeps perfect time.
I can't believe.

Total time start to finish, including coffee breaks, trips
to the 'Shack, explaining to my wife what we were doing,
etc. was about four hours.

- Jim