Analog soundhead channel issue

[David Ferguson]

I'm having an issue with my analogue optical sound head on a Kinoton projector I'd appreciate some advice/help with.

I'm getting no audio out of the left channel at all, only the right. I've traced back the wires from the connector on the side of the projector to the wires that enter the solar cell using a multimeter in continuity mode, and all three of left, right and common are fine. I've also put a voltmeter across the common and right/left wires, and I get a small voltage on the right channel when I shine a torch on the solar cell, but no voltage across the left channel. All of which leads me to believe it's the solar cell itself.

I've been running things in digital the past few months, so don't know exactly when it stopped working. But I do know it was working in January, albeit a little intermittently. At the time I thought it was the cable I made to go from the projector to the CP500, but it seems not due to the measurements I took as mentioned above.

Can a single channel of a solar cell die like this? Is there other tests I should do to check it? And can I still get a replacement anywhere? I'd rather test things and be very sure it's dead before I do a replacement, as I lack a buzz track and oscilloscope so alignment will be... tricky.

The projector is a Kinoton FP38EC, with the older style incandescent reader, rather than a red light or reverse scan one. I've included a picture below to be clear.

[Sam Chavez]

Individual solar cells can certainly die and although it's fairly rare outside of being mechanically damaged by a Mylar film accident, etc., I've had a few that seemed to die due to a static discharge off the film itself. I'd see this happening in the winter in dry cold rooms.

I'm interested in how you measured voltage across the cell. Open circuit, or loaded down at the input to the CP500? It's a very small Voltage to measure reliably.

Just to be sure, if you have not already done this, switch the left and right solar cell inputs at the 500 and run some film just to be certain it was the cell and not a shorted input at the 500.

I may have a couple of raw stereo cells I could send you in the post. Good luck trying to attach them to the arm though.

[David Ferguson]

I measured the voltage open circuit by just putting the multimeter across the + and - of each channel without the CP500 connected, and then shining a torch over it. It was a small voltage, in the tens of millivolts, but there was a clear change on the right channel, and no change at all on the left.

Later this week when I have time I'll try swapping round the left and right inputs to the CP500, in case that makes a difference - although I'm not holding out much hope at the moment!

I'm guessing by your comment that attaching the cell to the end of the arm is no easy task? Do they have wires on them, or does they need to be soldered on (not too big an issue, but I think I would need to get a smaller tip for my iron!)? And then of course there is the issue that I don't have any test film or an oscilloscope, so aligning it would be tricky.

[Mark Gulbrandsen]

Coming up next... "Scopes and Spectrum Analyzers" to properly align this A-Chain.

[Randy Stankey]

I agree with Mark.

Before you go tearing things apart, you need to be sure that your sound reader is properly aligned. You'll need some test films and, at minimum, an oscilloscope and a volt meter. You should also use an analyzer but you can get away without it for the time being. Once you get everything in the sound reader to be "plumb, level and square" you'll be able to tell if there is something wrong in the cell or the wiring but you could end up doing a lot of work for nothing if you don't align things first.

You can use an analyzer and tune things up, the rest of the way, after you are sure that everything else is working the way you want it to.

Your problem could just be happening because the horizontal alignment of your sound reader is off. All it would take to fix this is a strip of buzz track film. Although it's better to use a scope, you can do a quick and dirty job just by running the buzz track and adjusting the sound reader by ear.

That will get you in the ballpark so that you know whether your system works. Then, you can go back with a scope and analyzer and cross your "I's" and dot your "T's."

[Sam Chavez]

Likely the cell is bad, but just double checking.

The cells come with wiring, red, green, black common. Main issue is gluing the cell to the arm. Avoid the temptation to use Crazy Glue as it will run and end up on the cell face.

Ask me how I know.

[Frank Cox]

I know nothing about fixing this, but maybe a good glue for this purpose would be contact cement?

[Sam Chavez]

Imagine gluing down a tiny solar panel, essentially a glass surface and a metal backing. Better to use cement with a little open time to allow a perfect fit on the bracket and can be held in place with tape that won't stick to the glass surface as the glue or cement sets.

[David Ferguson]

In my non-professional, novice opinion, I don't think that it's an alignment issue, as although I first spotted the issue due to only hearing the right track, I did test it with a voltmeter and shining a torch on the solar cell, and the right channel showed a voltage, and the left did not. So I don't think any amount of alignment would help with that!

Although whether I try aligning it now, or get a new cell and have to align that, it seems I'll have to do alignment either way. Sadly the only alignment loop I have is cat 1010 for my digital soundhead, and it looks like I'll need quite a few for this (a guide showed the use of cats 69T, 69P, 97, 530, and SMPTE buzz track, and something called a "snake track"). So the big question is... where can I get those? I saw Orselli has some for sale, but these are cyan dye soundtrack, and I need the silver dye one. (I'm actually pleasantly surprised they're still being made new, even if it looks like they're being run off a Cinevator).

[Sam Chavez]

Several places still carry 35mm test film. Check for the gray hair. Although alignment is necessary, if you don't disturb the lens during the changing of the solar cell, it will still be in focus and azimuth will be the same as before.

[David Ferguson]

I had a bit of a surprise today when running a trailer as a test, as it started playing in stereo, ie. both channels were working. I got about 30 wonderful sounding seconds of The Lion King's Circle of Life, before it dropped back to just the right channel again.

Would a faulty solar cell be intermittent like this? I've double and triple checked the wiring from the CP500 to the solar cell, and it seems perfect, or at least the continuity meter shows they are all fine. It was a nice surprise to have the left channel working, and then odd (and sad!) for it to drop out - as I was listening and the film was playing!. There wasn't a splice, or anything else that went through the projector at the time, it just stopped.

[Sam Chavez]

It is possible to have an intermittent fault. There is a tiny bead of solder that holds the cell wiring to the cell face at the bottoml. Another thing to check is to determine where on the cell the slit of light lands. it should be about 2/3 up toward the top of the cell. If it's too high, with vibration from the motor shaking things, you'll end up with the slit missing the cell. Same idea with too low, as you end up in the cell wires.

As to the ohmmeter readings, I've never had much luck measuring anything meaningful on a cell. You have a sight voltage being produced unless you're measuring in total darkness. Also, it's quite capacitive and you can get false or confusing readings.

Last, I would not rule out an intermittent connection at the input to the 500. The db-9's are hard to solder properly.

[Randy Stankey]

I’m wondering about the integrity of the solder joints.

How old are the connections? Are they crusty, etc?
What kind of solder was used? We’re they done right?

Solder joints are funny. They can look good and work well for a while but, after some time, they can go bad for a whole host of reasons that you might not see until the joint starts to fail.

The place where I work does a lot of soldering and tinning for military and aerospace applications. The rules about how soldering is done are very specific.

In just tinning the leads on a D-sub board mount connector, there are about a dozen specific rules that have to be followed. For instance, the specific gravity of the solder flux has to be within a certain range.

If parts are tinned wrong… for instance, if the flux is out of spec, they are supposed to be scrapped even if they look good on visual inspection.

It’s kind of a long shot but, maybe, something like that is going on?