For the last year, my Elmo 16CL haven't been running. It is my main 16mm projector and is located at the cabin, and even though I have an old manual Bell & Howell at home, it is nothing like the ease of using the channel loading Elmo 16CL. So the last year, I haven't seen much 16mm. I have tried figuring out what was wrong, but my lack of electronic skills was just too evident.
In short it has had no sound. At least most of the time. If I ran it for a while, the sound would come back some times. All the fuses were ok. When the sound was gone, the exciter lamp was dead. Last weekend I took another closer look, and the amplifier worked even though the lamp was off. If I used an other lamp and lit into the sensor, I would get some audio. When the lamp was out, I got 0.5V on the lamp socket. It should have been 4V.
When I got back home, Greg had found two interesting links for me:
1. http://16mmfilmtalk.com/viewtopic.php?f=...ridge+rectifier - This is a forum post over at the 16mm film forum that described my problem exactly, with the same measurements to the lamp socket. It suggested I had a bad bridge rectifier.
2. A youtube video where someone made a step by step guide to replace the bridge rectifier on an 16CL:
The symptom of a bad rectifier on the 16CL was to have 0.5V on the lamp socket, just what I had, so I took the chance and ordered a new part from the US. It arrived in two days, so I got it in time for this weekend at the cabin.
I started by measuring the bridge rectifier to identify the problem, just as in the video. But to my disappointment it was not showing bad values. I checked many times to be sure I had measured tight. What a bummer. I started the projector and surely the lamp was off. I almost gave up, but made a new measurement. Now that the projector had been running, the measurements changed, and I got values that were off on one side. Could it be that it was the bridge rectifier after all? I took the chance of replacing it and soldered off the old one.
I love my soldering station. Before I got this, I had a cheap soldering iron. It was hard to use, and I thought it was just me being awful at it. But then I spent some money on a soldering station, and man what a difference! I suddenly felt like a pro! It heats up super quick, but as it has a temperature sensor at the tip, it makes sure not to keep on heating when the correct temperature is reached. Taking the soldering off is not what I am best at. I have a vacuum pump to suck the soldering off, but I am not good at it. I had better luck with copper laces. But off it went.
The new one is quite much larger than the old one. As the old is not longer possible to get, I got the same as in the video which has the same specifications, but is quite much larger:
The Elmo has two equal bridge rectifiers, and on the video you can see them at a 90 degree angle. And on the circuit board, you have nice prints with 4V, plus and minus etc. My projector must be a different revision as the two bridge rectifiers are parallel and the circuit board didn't have those nice printed texts. I had to make sure to note which way the plus and minus was placed from the old one before soldering it off.
The different layout on mine just made it impossible to get the new one in, It was simply not room for it between other parts. After trying for quite some time, I gave up and decided to solder on some cables instead.
The cables I had at the cabin were thin ones from a previous Arduino project with pins at the end. At home I have a lot more, but that didn't help me here. I had three only, and the bridge rectifier have four pins. So I had to cut one of them in two:
The rest was quite straight forward, soldering the cables on:
I added some tape to avoid making a short circuit as it is loose in there:
Finally I placed it where it was room for it, with a little tape to keep it in place:
I tested the machine after this, and voila! The machine worked with the exciter lamp on!
I was afraid the cable would get hot. I measured the voltage drop between one and and the other. It was 16.35V and 16.25V. Not much. And after running it for half an hour the cables were not hot. But that IS the bridge rectifier. I consider using some thermal paste I have for PC CPUs and a heat sink to get it a bit cooler, but I guess it is OK as it is.
That half hour of testing was also for making sure it was in fact repaired! The exciter lamp sometimes lit for a few minutes when I ran it before the fix. So it COULD be that the first test was just pure luck and the new bridge rectifier had nothing to do with it working at the moment. But it ran smoothly for that entire half hour, so now I am pretty sure it is working. I am super excited and very ready for watching some more 16mm films again!
A BIG thanks to Greg for providing me with the two links that made all the difference for me getting it fixed!
