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Home > Technical Articles > VDO Clock Repair

Guest Technical Article
VDO Clock Repair


Forward by Wayne:

     Demick Boyden has written us a fine article on how to repair your VDO clock.  The mechanisms from the various Porsche cars are very similar.  Although Demick speaks specifically of the 914, the VDO clocks that are used within the other Porsche models all share a similar mechanism, and the similar repair problems.  This article details the problems with the internal electrical solder connections that often fail.  There are a few other problems with the clocks that cannot be repared without special parts, such as new pendulum springs.  For clocks that need this additional repair, please contact Pelican Parts.

Figure 1:
Two Different Clock Mechanisms
VDO Clock Repair

     There are two types of clocks styles available in the 914 that I am aware of. Both look identical from the front, but are easily differentiated from the rear and have very different mechanisms inside. Both are shown in Figure 1. In the spirit of VW, I will refer to the clock on the left as Type I and the clock on the right as Type II. To the best of my knowledge, the Type I clock is the earlier model, and the Type II clock replaced it in 1973.

     Comparing the two clocks, I like Type I much better. It is much easier to open up and you will have a much greater chance of successfully making repairs. Also, Type I has a way to externally adjust the speed at which the clock runs so you can dial it in to be quite accurate. Type II has a different clock mechanism which presumably eliminates the need for adjustment (since there is no external adjustment, although I believe there is an internal adjustment), but I have never had experience with an operating Type II clock so I cannot verify its accuracy.

Figure 2:
Standard 3 Gauge Set on the 914

Type I

     The Type I clock has an easily removable rear cover. Three small nuts are all it takes to remove the rear cover (you may need to break the small plastic that goes around these nuts if the clock has never been opened up before). Inside you will find a series of gears and a coil and a couple of springs (Figure 2). There is a steel disk about " in diameter near the rear end of the clock which has an electrical contact mounted under it. When this electrical contact is closed, current is sent to the coil which spins the steel disk around about turn. This is how the clock is wound. The disk is spring loaded and will slowly over the course of about 3-4 minutes return to its original position - operating the clock as it goes around. When the contacts close again, the process starts all over again. For this reason, this clock only uses power for a fraction of a second every 3-4 minutes. You can turn the disk manually and see how this all works. The rest of clock works like a regular clock with all of the gears, etc.

Figure 3:
Standard 3 Gauge Set on the 914
     This clock has a built-in fuse, which is what is normally the cause of this clock not working. Right next to the coil is a set of metal tabs which should be soldered together (Figure 3). If your clock is not working, chances are that these two tabs are no longer soldered. The process to repair it is simple: resolder the connection. To do this correctly, you need to use a low temperature solder (specification is solder with a fusing point of 120C or 248F). Where to find this? I don’t really know. I had some low temperature solder laying around which came in strips and was designed to be wrapped around a wire and then melted with a match. It never worked good like that, but it worked fine in this application (minus the match). I don’t know what the actual fusing point of this solder was though. Using regular solder is an option that will work fine, but someday your clock will really get fried because this fuse didn’t melt like it was supposed to and you will not be able to repair it. The choice is up to you. Also, when you solder the two tabs together, be sure that the top tab is pulled down (so it is spring loaded) to meet the other tab and then soldered. Don’t try to bridge the large gap because this spring loading is what helps to separate the tabs when the fuse melts. Note: The solder job shown is Figure 3 is NOT done correctly for exactly this reason (big blob of solder bridging the gap)

     Well, that’s about it! Put the rear cover back on and plug it in. Adjustment of the clock speed is made by the small slotted screw which protrudes through the rear cover. Counter-clockwise goes faster. Best that I can tell, each 1/8 of a turn affects the clock by about 5 minutes per day.

Figure 4:
Standard 3 Gauge Set on the 914

Figure 5:
Standard 3 Gauge Set on the 914

Figure 6:
Standard 3 Gauge Set on the 914

Figure 7:
Standard 3 Gauge Set on the 914

Type II

     Getting inside the Type II clock is a bit more difficult. Just like most all of the other 914 instrumentation, it involves using a sharp object (small screwdriver, chisel, etc) and carefully prying around the outside of the outer face ring. This part is a real pain. You will have to pry the formed flange up for at least of the way around the clock, and then remove the clock ring and glass from the rest of the canister. Now it is time to remove the guts of the clock from the canister: remove the 3 screws from the rear surface of the clock and unsolder the ground connection (Figure 4). The guts of the clock should now slide out (Figure 5).

     Once open, you will notice that the inside looks quite different from the Type I clock. This clock is run by an electric motor rather than a spring loaded disk wound by a coil. The most common failure with this type of clock is a damaged gear. In my case, it was a gear whose support shaft had broken. In order to fix this shaft, I wanted to separate the PCB portion of the clock from the gear portion (shown separated in Figure 6). This is possible to do given the following: Remove the obvious screw which holds the PCB on, and unsolder the two posts which are arrowed in Figure 7. These two posts are how the electrical connection is made to the electric motor. If you do not unsolder these posts, the PCB is still very easy to remove, but your clock will never work again. The posts will come out with the PCB, but the very fine wires which go into the motor will break and there is no way to re-connect them (I know, I’ve tried - that’s why the motor in Figure 7 is partially cut open). With the PCB removed, you can get access to do the gear repair. In my clock, I did the gear repair very carefully with epoxy, and then found out on re-assembly about the broken wires - but I am confident that the repairs would have worked had I not broken the wires.

     Re-assembly is just the reverse of this process. Test the clock before putting it completely back together (that face ring is really a pain - you don’t want to do it twice). Also, note in Figure 6 that there is an adjustment pot mounted to the PCB. I believe that this pot is the clock speed adjustment and it is not accessible except by clock dis-assembly.

     That’s about all of the tips that I have, so good luck in your 914 clock repairs! There are not all that many 914 clocks that still work. Maybe with this information, there will soon be a few more....

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