VDO Mechanical Clock Repair: Use inline Thermal Fuse?

[DSouth]

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=2032058.2032234.2032300&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.

[dlagerstrom]

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.

[DSouth]

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?

[DSouth]

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?

[dshepp806]

Originally Posted by DSouth

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=2032058.2032234.2032300&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.

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.

[Jim727]

Question for Electrical Experts

[dlagerstrom]

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?

[DSouth]

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....