8mm Forum: Yelco P-111B and the Mystery Diode

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Posted by Steve Klare (Member # 12) on August 14, 2015, 08:37 PM:

Last year my son told me he wanted a projector of his own, so I revived a dead Yelco P-111B and gave it to him.

The machine runs fine, but the picture is beyond dim: whites are gray, it can't handle more than a TV sized screen without washing out. When he uses it at CineSea in daylight conditions he's down to an A sized sheet to be visible at all.

This uses a 50W lamp, so nobody expects it to burn holes through the screen, but it seems to me it should be a lot brighter than this. I've had other 50W machines that weren't like this.

-so I poked around...

Transformer output for the lamp: 8 Volts, fine! Lamp voltage? 3.9V! This is less than half what it should be, so the lamp power is less than a quarter what IT should be! This is under 12.5 Watts, about two editor bulbs...

I noticed something funny: the lamp circuit seems to have a diode inserted in it. Now this starts to make sense: you only let AC current flow one way, you lose the current when it doesn't flow the other.

-half the current, half the voltage, one quarter the power.

My guess is the former owner was using the machine on a small screen and cut back the brightness to stretch his lamp life. I knew the guy: he's a fellow electronics guy and doing this is definitely something he could pull off.

My question for any other owners of Yelco P-111Bs is when you look at the back of your machine near the base, do you see this hex nut on a stud passing through the chassis?

-I'm guessing: "No!".

This is something new here: we deal with machines that are worn out and damaged all the time. This may be the first sabotage!

Posted by Andrew Woodcock (Member # 3260) on August 14, 2015, 09:10 PM:

Jeez Steve, this is one Dog of a machine! get your son something decent if you wish for him to carry on the mantle.

[ August 15, 2015, 06:07 AM: Message edited by: Andrew Woodcock ]

Posted by Steve Klare (Member # 12) on August 14, 2015, 09:33 PM:

Forgot our tact pills today, did we, Andrew?

What part of your answer is helpful to me here?

(If you have nothing nice to say...)

Posted by Andrew Woodcock (Member # 3260) on August 14, 2015, 09:34 PM:

Oh dear!

In answer to your question Steve, I guess we can safely say the answer is NO.

Posted by Steve Klare (Member # 12) on August 14, 2015, 09:41 PM:

To get back to my question: Does anybody here have one of these machines?

Posted by Mathew James (Member # 4581) on August 15, 2015, 09:22 AM:

Hi Steve,
I tried looking for this one to see if I could find a rotated view of the projector to see if the nut was there, but I cannot find anything....
This looks to be your machine here?
http://www.youtube.com/watch?v=YkmnzasH7X0

Other Info:
marketed in 1969-70
standard 8 mm \ super 8 mm film
format change: auto, by lever
lens: Zoom f: 1.3 \ F: 15-25 mm
lamp: 50 W, 8 V, CXR
reel capacity: 120 m
projection: forward, reverse
projection speed: variable speed
variable speed control: by rheostat
film loading: fully automatic reel to reel threading
sound: no
motor: DC magnetic motor
power source: 93-100-110-125-160-230-240 V AC, 50/60 Hz
weight: ?
dimensions: ?
made in Japan by Yamawa

Your pic may be the only uploaded back view of this one. Sorry I cannot help further.

btw- this looks like it was also marketed as another machine here:
http://www.super8data.com/database/projectors_list/projectors_ifba/ifba_quartz.htm

Posted by Dominique De Bast (Member # 3798) on August 15, 2015, 09:42 AM:

Mathew, I think that the Ifba Quartz P 111 Q is the same model as the Yelco P-111Q, which is a different projector than the Yelco P-111B.

Posted by Barry Fritz (Member # 1865) on August 15, 2015, 11:35 AM:

Dominique is correct. The main difference is the 111B has the old spaceman CXR lamp which is getting quite expensive.

Posted by Mathew James (Member # 4581) on August 15, 2015, 04:37 PM:

Thanx Dominique for the clarification!

Posted by Steve Klare (Member # 12) on August 15, 2015, 06:20 PM:

That is indeed the machine: it's actually a nice simple little projector with continuously variable frame rate. A lot of people like them for telecine.

In my case I just wanted something user friendly to give to my 12 year old (now newly 13) so he could have his own.

-it's kind of neat how well a kid of the "app" generation adapted to changing sprockets and aperture, framing, focusing and rewinding!

I have a little more pondering and measuring to do, but my gut is telling me once I bypass that diode things will get a lot brighter.

-next step: go through it with an ohmmeter, pencil and paper, trace the circuit and make sure my gut knows what it's talking about.

I did find him a spare spaceman lamp: worked out to about a buck an hour for the rated life! By the same token at the rate he uses it showing 200 foot silents, the two bulbs should last him until college, or Eumig or Elmo (Whichever comes first!).

Posted by Steve Klare (Member # 12) on September 27, 2015, 09:30 PM:

I thought this story deserved an epilogue.

I traced out that circuit and found that the old friend that gave me that machine years ago did indeed do a little surgery on it. He clipped the unswitched wire from the grounded side of the lamp and soldered it to the anode of a diode he'd installed through a hole drilled in the chassis.

Why? My best guess is he was trying to stretch out the life of the lamp by cutting the operating voltage in half. It would easily get him 50 hours out of this 25 hour bulb.

Problem is that when we are at CineSea we are running pretty much at daylight conditions all day long and the biggest "screen" he could manage with the great big 12.5 Watts he had in that lamp is a card film box!

-still the same. When you are 12 years old and you have a sleeve of Ritz crackers, new sneakers AND your own movie projector, life is good!

I put the wire back where Yelco meant it all along (-could see where he clipped it!). Post-surgery he showed us a reel tonight: not exactly Xenon, but much improved. This time he will smoke that screen with 50 mighty Watts!

I very much doubt we will ever hear this again: that legions of Yelcophiles will thank me for showing them their parasitic diodes, but at least the story has a happy ending!

Posted by Janice Glesser (Member # 2758) on September 28, 2015, 12:08 AM:

Steve ... your son is adorable and he looks so content next to that little projector. This is a great story. Your son will always remember that projector as a bond he had with you. Good job Dad!

Posted by Graham Ritchie (Member # 559) on September 28, 2015, 12:25 AM:

Steve

You might find this of interest.

Posted by Dominique De Bast (Member # 3798) on September 28, 2015, 01:36 AM:

Well done, Steve !

Posted by Steve Klare (Member # 12) on September 28, 2015, 08:57 AM:

Thanks Guys and Gal!

That's really interesting Graham. So it was a do it yourself Hi-Lo switch, but all we got was "Lo"! I wish he'd done the switch as well: I would gladly have left it alone.

I think this is actually good for Steven. Everything he deals with is software: Apps, Games, Uploads! This essential knowledge these days, but I think it's good to understand motors, gears, belts and pulleys too! Someday when there's steam pouring out of his radiator cap, a little mechanical horse-sense will serve him well!

(I'm grateful for it every time the garage door or the dishwasher goes into rebellion!)

This also says a lot for the people at CineSea. He walks around the place like one of the Veterans and the guys make a point of putting interesting stuff on screen for him. Besides, that picture only ever happened because Doug was willing to clear a spot on his table for him.

I'd love to know what he was watching here. I'm betting the title isn't "Homework"!

Posted by Martin Jones (Member # 1163) on September 28, 2015, 10:40 AM:

Do projectors have radiator caps?

Posted by Steve Klare (Member # 12) on September 28, 2015, 10:47 AM:

General knowledge is generally applicable!

There's certainly a lot going on here in terms of power, cooling, temperature and even over-temperature that you can't understand the green fog condensing on your windshield until you pretty firmly grasp.

Not to worry: There's a lot of intermediate steps between the projector and a car, but he has to start somewhere.

Posted by Graham Ritchie (Member # 559) on September 29, 2015, 12:12 AM:

I think its very important for young people to grasp how things work as much as possible and if they can "visualize" the big picture, then if they have a problem, hopefully that in turn will give them a better understanding how they might be able to fix it. [Smile]

Posted by Steve Klare (Member # 12) on September 29, 2015, 08:21 AM:

There's a certain feel for how things work that you actually get from working those things.

-as good as simulations may be they will never develop these instincts in people.

It's like when you are driving your car: you start to sense something isn't right even before you can describe why. As soon as you can you start checking things out and maybe catch the problem while it's still a small one.

Without this you will drive until a major piece falls off or something bursts into flames!

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