This is a long boring response to some technical questions that someone asked me about the door lock module. Some of you might find this interesting. This was in response to my original post on the DML, Theory of operation (was Diode in Lock Module): QUESTIONS: My question based on your findings: Yellow diode blew. Have you come up with a replacement since you wrote your article?? If the diode is protection, would the door locks work without it?? If not, are there any other parts that could be replaced that would have been damaged?? Here is the lock modification link that I plan to use: ftp://dmcnews.com/pub/lockmod91.pdf ANSWERS: > Have you come up with a replacement since you wrote your article?? No, I'm using the LockZilla with the optional Zilla remote. So I haven't been motivated to refurbish my OEM module. The diode burns out because it is too weak for the job. I suggest replacing it with something that can handle a lot of current without being excessively bulky. I would choose one by just going to Radio Shack and picking one off the wall that looks good. > If the diode is protection, would the door locks work without it?? Yes, certainly. The diode can only supply protection against reverse-polarity surges. If you tried to use a diode the other way, it would conduct the battery voltage to ground and burn out. Think of a diode as a one-way valve for electricity. As it is used in the door lock module, it works great for shunting reverse-polarity surges but totally ignores forward-polarity surges. A diode is unable to tell the difference between battery voltage (+12 volts) and a positive surge (something greater than +12 volts but likely not more than +100 volts). I'm curious to walking into a custom car audio shop to see if they sell any general purpose surge protectors that would protect positive as well as negative surges. I hope I haven't lost you in the technical jargon. The diode is primarily protecting the rest of the door lock module, but it also protects the whole car per se. Even while the car is not running, the diode is still connected across the battery. You could put a dozen of these diodes at different points throughout the car and it wouldn't make much of a difference. The diode tends to protect the devices that it is closest to. This is the nature of surges. They can happen very quickly and tend to act kind of like lightening. You never know what path lightening will take, but the path it does take is generally the shortest one. In comparison, a diode at the power input to a device tends to shunt spikes going into the module. It also shunts spikes generated within the module. > If not, are there any other parts that could be replaced that would have been damaged?? Not likely. The most sensitive parts in any device are the semi-conductor junctions. These include other diodes & transistors. So in the case of the door lock module, the most likely ones to be damaged are the transistors driving the relays. It has been a while since I looked at the link: > ftp://dmcnews.com/pub/lockmod91.pdf At the time I glanced it over and have not yet read all of it. I trust that the transistor that the author suggests for replacement is well suited for the job. In fact, there are probably dozens of readily available transistors that would make fine replacements. To choose one on your own, you need to be familiar with how to read the cross-over books to make a reasonable choice. If the transistors in your module work, you are probably just as well to leave them alone. The fatal flaw that I noticed in ftp://dmcnews.com/pub/lockmod91.pdf is that the author replaced the relays with ones that weren't much better. I remember him stating that he was planning on replacing these relays occasionally as a maintenance issue which to me sounds ridiculous. Fix it right the first time and be done with it forever more! The fatal flaw with the design of the OEM module is that the relays de-energize slowly meaning that the contacts open gradually. In the process, this allows the current they carry to spark & arc which does unacceptable harm to them in short order. I have heard of two fixes that are reasonable. I'll explain them as follows: Method 1: Keep the OEM relays or equivalent ones in there, but instead of having them drive the door lock solenoids, have them drive larger relays instead. Then these larger relays drive the solenoids. How this is an improvement is that even though the original relays are still switched slowly, they are switching much less current because they are only driving a slightly larger relay instead of the solenoid. So the original relay's contacts will last considerably longer. Since the larger relay is being switched by the smaller relay, there are no problems with the contacts of it releasing slowly and burning. To me this seems like an acceptable fix but is a little too much of a Rube Goldberg contraption for my tastes. Method 2: This one is promoted by Martin Gutkowski. The fix is to replace the weak OEM relays with better ones that are hermetically sealed (air tight with inert gas inside). Even though the relay contacts are still released slowly which promote arching, the contacts have no flammable air around to burn them. I consider this an elegant fix and admire Martin's ability to have thought this through. The last I heard, Martin was offering for people to send him their old modules for upgrades using the sealed relays he found. He was willing to do this at minimal cost. You might want to ask him about it. Or if you are handy with a soldering iron, maybe he can tell you where he found those relays as I know sealed ones are rather unusual and hard to find. Many people got tired of this discussion on the DML, so at my suggestion Martin started an alternate Yahoo news group titled DeLorean Electrics. I suggest you subscribe to this list and read the archives since it will tell you more about upgrading the relays. http://groups.yahoo.com/group/dmc_electrics A while back I had a falling out with the DML moderators with their precarious & inconsistent standards and started an unmoderated newsgroup, the DMCForum. I invite you to subscribe & participate. For now the only way to subscribe is to the unmoderated version through Yahoo. Soon members will have the option of subscribing to a moderated & highly organized digest version with the goal that it will make topic threads easy to follow. The link for it is at: http://groups.yahoo.com/group/DMCForum There is a prototype of the DMCForum official web site at: http://216.167.99.38/ It is just a shell of a website now, but the authors are still writing it. Check it out. Walt To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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