8mm Forum: Bolex 18-5 Lamp Not Working

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Posted by Russell Bowman (Member # 3447) on December 31, 2012, 03:21 PM:

After many years of storage, I'm tring to get Bolex Pailard 18-5 working. Every things seems to function except the lamp. I measured the voltage at the lmap socket as approx 9.4 volts without the lamp installed. It measures at 0 volts with the lamp installed. I have three 8v 50 watt bulbs. They all show good continunity but none will light.

I wandering if there is a bad electrical component which is preventing the current from passing to the bulb once a load is applied. Does anyone have any thoughts on this or know were I can find a service manual or electrical diagram?

Thanks,

Posted by Steve Klare (Member # 12) on December 31, 2012, 04:17 PM:

Hi Russ,

Welcome!

It sounds like some high-ish resistance between the source powering the bulb and the bulb itself. It's not an open circuit but not a great connection either.

An 8V 50W bulb should have a (hot) resistance of about 1.3 Ohms (cold resistance even lower). A typical voltmeter runs about 10 Million Ohms. So a series resistance of let's say even 10 Ohms will load down like crazy with the bulb, but barely at all with the voltmeter.

I think if you unplug the power and start poking around looking at the resistances of that circuit you should be able to see where that excess resistance is.

My New Years Eve bet?

-the switch that turns the bulb on and off. These contacts take a huge beating powering up the bulb and may be burned and oxidized.

If I'm wrong: sorry, I'm on vacation until Wednesday. I must be saving it up for work!

Posted by Russell Bowman (Member # 3447) on December 31, 2012, 04:45 PM:

Thanks Steve. I thought about the switch but was unsure on how to get the red knob off without breaking it. That needs to come off so I can remove the faceplate and see the contacts. The motor works fine so I am guessing there must be two sets of contacts.

I took the side cover off but cant really see much without disassembing the unit. Is there any other electronics between the transformer and the bulb other than the switch?

Thanks

Posted by Steve Klare (Member # 12) on December 31, 2012, 04:58 PM:

I guess there could be a fuse. I don't think that's a great suspect here though.

I don't know this machine very well (really at all...), but on the Elmo projectors I do know there are multiple lever action switches for various functions (lamp, motor forward, motor reverse). These are activated by pressing on cams turned by the control knob. When the lobe of the cam rides under the switch the lever is pressed in and the switch is closed.

The joy of it is it should be a simple circuit, so there are only so many things that could be the problem.

Does this machine have a seperate lamp switch apart from the control knob?

As I remember it, this one is one that Paul Adsett knows quite well.

For myself, I'm a Ford guy trying to fix a Dodge here! I have the big idea but don't know specifics!

Posted by Russell Bowman (Member # 3447) on February 08, 2013, 08:37 AM:

Anybody else have any thoughts on this before I just tear into the projector?

Posted by Andy Katz (Member # 3506) on February 08, 2013, 09:24 AM:

Silly question, but you did clean the bulb contacts, and the contact on the bulb itself? My bulb didn't work, until I bumped it with my finger and got it going. Turns out the contacts were all tarnished, causing the bulb power to cut in and out.

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