Elmo GP-E SZ model

[Thomas Dafnides]

I just picked up an Elmo Gp-e SZ, As Is /Parts. I got it running, but with one problem. It is running to fast. The Rheostat will regulate the projector from est. 22-38fps. Looking at the rheostat from the inside , the circle coils are covered with an heavy green coating... I am not sure if this is corrosion (does not appear anywhere else) or an industrial coating applied by Elmo. Does anyone recall the rheostat on your Elmo Gp to have the green coating on the rheostat coil ? (I have the voltage setting set to 125V). New belt installed. I sprayed the coil heavily, with contact cleaner .... nothing cane off. I am not sure if I should attempt to scrape it off, considering it maybe an intentional coating.

[Steve Klare]

Hi Thomas,

Since you are getting variability in frame rate, I'd sat your rheostat is doing the job. The green coating sounds like some enamel that is baked onto the wire to protect it. (This should be absent at the point of contact between the wiper and the windings.)

My wild guess is maybe the routing of your belt isn't correct. All I have is the fact that you changed it, and that's what makes the guess a wild one.

[Thomas Dafnides]

Steve, Thank you for your expertise and help. Looking at a ebay photo on the internet, the routing is correct (unless of course, the photo is not correct). The routing seems straight forward. The two wires that connect to the motor....can a resistor be planted there to reduce voltage? When I set the voltage selector to 220v , it actually runs correct speed. But, of course, the Bulb's light output is greatly, diminished. So it seems the voltage has to lowered to the motor only. I will look for more belt photo configurations to confirm.

[Steve Klare]

The problem here is there are so many explanations for "too slow", but not a lot for "too fast". It's like somebody bringing their car to the mechanic and saying "All of a sudden, my gas mileage has gone up.".

It almost feels like there are multiple secondary taps on the transformer and somebody re-wired your motor circuit into the wrong one.

Does the motor have a ratings plate on it stating an operating voltage?

(Do you have a voltmeter handy?)

[Thomas Dafnides]

Motor has no ratinga plate. If I pick up an inexpensive voltmeter (good enough?), what/ where would I measure?

[Steve Klare]

The idea is that the motor circuit needs to be connected to power, and that means connections to the proper taps on the power transformer.

Even if you don't have a meter, you may be able to figure this out.

Let's start by unplugging the machine: the hot end of the transformer is plenty dangerous and it's right there! (Work Safe!)

HEY!

I found a schematic! It's in French, but I had about 6 weeks of that when I was in the fifth grade! (I DO speak "schematic", though!).

Elmo schematics aren't always easy to find: this is great!

So there is our motor circuit (well, really "your" motor circuit!). We have your motor, a run-stop-reverse selector switch, a filter cap and a rectifier. According to this, there should be a red wire from the rheostat to a terminal marked "60V". There should be one wire from the rectifier assembly to the terminal marked 115V and a second one to the same terminal as the black wire from the plug.

This doesn't look very complex: there should be enough information here to trace it out.

"jaune" is for the yellow wire from the plug. (I guess that's where "jaundice" comes from!)

[Brian Fretwell]

And Rouge can be from the colour powder Frrench women put on their cheeks.

[Steve Klare]

Yes, and some things don't translate very well. "Baton Rouge, Louisiana" sounds just great in the original French, but if you translate it to English you wind up with "Red Stick".

-Imagine seeing that on a tourism brochure!

The transformer in this machine is an interesting one. Other than the 5V accessory winding it's what's called an autotransformer: only a primary winding with taps: no isolation input to output. Just like any transformer, all the windings have the voltage they are designed to produce whether or not they are being used, as long as any of the others also do. For example, if Thomas selects "125V" on the voltage selector and plugs it into North American 125V, there will still be voltages induced on the other windings up to and including 240V up at the top. If he goes to Japan, selects 100V and plugs into 100V, the exact same voltages will be on all the other taps. If he goes to Europe and does 240V, still the same.

So, if somebody connected the rectifier connection meant for 115V to let's say 200V, 220V or 240V, there will be too much motor voltage and it will go too fast. (-and eventually that 80V capacitor would blow sky-high!)

Another interesting transformer-thing is if you short-circuit any winding, anywhere in the device, all the others will act shorted too.