VDO Mechanical Clock Repair: Use inline Thermal Fuse?
 

Hi All,
I've been looking around the board and found a few threads on repairing the old VDO mechanical clocks. I decided to have a look at mine. I see if it was the same broken thermo solder link as many others. I've seen a few repairs where a more or less regular wire link is used to connect the two terminals and get the clock running again.

I've been wondering though if it makes sense to use a true thermal fuse to connect the two points, like this one:
http://www.radioshack.com/product/index.jsp?productId=2062259&cp=2032058.2032234.203 2300&parentPage=family

Its thresholds are very close to those specified on the clock cover(120 C or 248 F degrees), at 128°C (262.4°F).

My understanding is that resistance from "gummy" oil on the watch-train shouldn't have any impact on increased electrical resistance to the winding mechanism, but this just makes me wonder why Porsche/VDO makes such a big deal about using the right low temp solder for this specific connection. Is it really just meant to work as a fused link? If that's the case then I might conclude that an inline fuse before on the positive lead to the clock should suffice. Thoughts? I can post pics of my clock if that helps.

My understanding is that it is simply a fused link.

I ended up putting a small diode in the circuit as I could not find any low temp solder. I have blown up so many diodes with over current in my days, I thought it would make a nice 'fuse' so to speak.

In theory, I guess a fuse in front of the clock makes sense.

My diode has been running for about 3 years now with no issues.

Dave,

When you say small diode, how small are we talking here. Any specifics on it? Something that can be found an Radioshack or some other electronics store?

Dave,

When you say small diode, how small are we talking here. Any specifics on it? Something that can be found an Radioshack or some other electronics store?

Have you the circuit print for the clock? I'll have a look around the group, as I'm quite curious as to the components' function in the circuit. I would hardly think a wire install would be correct substitute (insofar as this type of component is concerned) I wouldn't necc. equate "thermal protection" as being the same as "overcurrent protection" (fuse), at all. Why aren't most people just installing the correct component? (Just wondering) ...

My best,

Doyle


Post a circuit print, if possible.

I don't have a circuit diagram at my fingertips. There are some good threads if you do a search. The diode I used was nothing specific, just a small one I had in my kit. I don't remember the specs.

The purpose of the low temp solder is to create a fuseable link. That is even what it is called. The issue is that it is difficult to find this low temp solder. As I understand it, the reason the solder/link would fail is if it gets too hot and this would be caused by an over-current situation. Meaning, a low current fuse would provide the same protection. Or am I all wet?

Thanks everyone. I did a search but hadn't found the thread that Jim727 posted here. That thread seems to support a thermal fuse in place of the hard to find(if not impossible to find) low temp solder. I think I'm going to go this route. I've learned a great deal from this forum, so I'll post pictures of my repair work, in the hopes that it will help someone else in the future. More to come....