MOVs are wonderful devices. I never knew anything about them until I had a problem with my 1983 Gold Wing Aspencade. That bike had a digital gauge cluster, and it had a MOV on it too, between the main power lead coming in and chassis ground. It was rated at 16 VDC or something like that. It's purpose was to shunt excess voltage to ground when voltage spikes occurred in order to protect the digital cluster. Sort of like a voltage relief valve, it would pass current if the voltage rose above a certain point.
So, here I am, out for a leisurely ride one evening in August of 2000 (yes I remember the date!) when the bike starts to miss and act up. I put on the brake to pull over and as soon as I did so, it straightened right out. Very odd. Let off the brake, and it started to balk and misfire. Step on the brake and it ran fine. So, I turned around and headed for home while keeping the brake engaged just enough to keep the brake light lit. Next thing you know, it started to miss again. I put the headlight on high beam and kept the brake on, and it ran fine. All this time my mind was not comprehending what was actually happening until I suddenly had lots of smoke come out of the gauge cluster and everything went dead. Engine, lights, you name it, nothing would work.
Managed to get the bike home (that's another tale that I do not wish to go into at this moment) and tore the cluster apart. Every light bulb in it was toast, as well as the headlamp, the tail/brake lamp, and a couple of scorched spots on the circuit board for the cluster. Not good. Found that the main fuse was toast too and quickly surmised that the voltage regulator had gone south and was letting everything charge full tilt. Replace the regulator and the main fuse and all of the bulbs and everything worked fine except for the cluster. Checked with Honda for the cost on a new board.... over $800 and that was back in 2000! That kind of money was out of the question, as I could retrofit the bike with a used cluster from the Interstate model for about $150, but I thought I would try a couple other things. I called every speedo shop on the planet; nobody would even touch it once they found out it was for something other than GM or Ford. As soon as I said Honda they would scream and cry like they had been hit with a hot poker and said "Nope, no way, can't help ya, g'bye!"
Not one to be beat, I knew that somebody somewhere would know what the story was, so just for grins and giggles I took it to a shop that did work on DC motor drives and on VFDs. They were a vendor for the company that I worked for, and I spoke with them on a rather regular basis, so I gave them a call. They said "Sure, bring it over, we're always up for a challenge!" and away I went. Upon arrival at their shop, I told the story of what had happened and one of the techs said, "I know what the two burnt parts are. One is a MOV, it goes right here (pointing out where it belonged) and the other is a resistor." He told me what parts to get from Radio Shack and I asked what I owed him. "Nothing! It's for a bike, that's all that counts!" I was dumbstruck. I tried to pay him, but he would not hear of it.
So, I paid a visit to my local Radio Shack and ordered two of the MOV's at $.69 each, and the resistor I needed, for a grand total of about $4 with shipping costs. A few days later, the parts arrived, and I diligently soldered them in to their respective places on the board, reassembled everything, and then very nervously hooked up the bike's battery. Nothing. Turned on the key..... and..... VIOLA!!! The gauge cluster was working! I don't think I have ever been so elated or relieved as at that moment!
Sorry about getting off topic, but this is one story that I always love to share!
