8mm Forum: Capacitors for Tower (Revere) P-911

This is topic Capacitors for Tower (Revere) P-911 in forum 8mm Forum at 8mm Forum.

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Posted by Gene Bachman (Member # 2547) on April 27, 2011, 03:23 PM:

I am a new member with a problem. I was tasked with copying the family 8mm videos from the 50's and 60's using the original projector from my wife's grandfather. The projector is a Tower P-911 made for Sears by Revere. After playing 5 400ft reels last night, I turned off the projector for the evening but did not unplug it. Several hours later, the projector started hissing and smoke came out. It was unplugged. I took the unit apart (I have had to do this numberous times for other repairs) and could find nothing obviously wrong. However on plugging it in, sparks and smoke could be seen coming from the large wax/paper capacitor connected to the power cord.

There are two capacitors in the projector. I would like to replace both capacitors but one doesn't have a number. The bad capacitor is 1.0 mfd 450V wax/paper. The other has two wires coming out of the top and a ground wire coming out of the bottom. Anyone know what I should replace these capacitors with? And where they might be available? Picture of the capacitors is below:

Posted by Martin Jones (Member # 1163) on April 27, 2011, 04:28 PM:

Gene,
I do not know the specific projector, and the pictures don't show on my Computer. Email them to me if you like.
But I can tell you that complete removal of either or both capacitors will not affect the performance of the projector in any way: this combination of three capacitors in "delta" form(one from each of the power lines to ground and one across the power lines) was commonly provided for interference suppression on Radio and TV broadcasts. That will enable you to continue with the tasks.
Martin

Posted by Gene Bachman (Member # 2547) on April 27, 2011, 07:20 PM:

Martin, I followed your advice and removed the large capacitor from the circuit. Now when I plug the projector in, the lamp comes on immediately without being switched on. Everything else seems to work fine but I am concerned about not being able to cool the lamp down after use. Any suggestions?

Posted by Steve Klare (Member # 12) on April 27, 2011, 07:58 PM:

I had this exact problem with one of my Elmo machines. It was simply that the lamp switch (in this case a pressure activated switch worked by a cam on the selector knob shaft) was sticking now and then.

While I had the machine torn down to replace the motor I replaced the switch too. I haven't had any more trouble with it in two years since.

Hopefully if you trace the wiring from the bulb you'll find some switch between the bulb and its power supply that you can replace or if you're really lucky find that the wiring on either terminal of it is simply shorted.

(Do you have an Ohmeter?)

PS: Are you sure that other than the capacitor you got the wiring back the way it started?

Posted by Gene Bachman (Member # 2547) on April 27, 2011, 08:26 PM:

The capacitor that I removed was in series with the hot wire to the bulb. There is really no way I could have miss wired it. I just reconnected the wires that went to the capacitor. The motor/lamp switch is a three way that is first motor then motor and bulb. I took it apart and cleaned the contacts and am pretty sure it is not sticking. If it was sticking, the motor should be running too.

Posted by Steve Klare (Member # 12) on April 27, 2011, 10:38 PM:

Basically it comes down to either the switch sticking or having a sneak path around it. This is where the ohmeter comes in.

The ideal thing to do is unplug the machine, remove the bulb and measure the resistance from the switched side lamp terminal to the the supply. With the switch on the resistance falls way down, with the switch on it goes way up. Anything else happenening is a problem. Finding out why and fixing it is the solution.

I don't know the machine (or the switch), but if the bulb and motor have their own set of contacts it is possible for one set to fail and leave the other still working. Since the motor and lamp should be able to function independently I'd think they do.

Posted by Gene Bachman (Member # 2547) on April 28, 2011, 12:46 PM:

I think the capacitor acts as a line filter on the AC feed. I don't see polarity indications on the capacitor so I don't know if it is electrolytic or non-electrolytic. Would it matter if I replaced it with the wrong type?

Posted by Steve Klare (Member # 12) on April 28, 2011, 01:53 PM:

Most electrolytics are polarized (non polarized electrolytics being the exception). If you put a polarized electrolytic in a place where the voltage is going to be reversed it will pretty quickly stop being a capacitor and turn into a low level explosive device instead. (been there...done that!)

Here's a 1uF, 450V film cap (non-polar) that's not a direct mechanical drop-in, but should be usable:

Capacitor

Posted by Gene Bachman (Member # 2547) on April 28, 2011, 04:48 PM:

Thanks, Steve. I ordered that capacitor. I'll let you know how it works.

Posted by Gene Bachman (Member # 2547) on May 02, 2011, 08:25 PM:

Installed the new capacitor and the projector works like new. Thanks for everyone's help.

Posted by Steve Klare (Member # 12) on May 02, 2011, 09:46 PM:

Cool!,

I'd love to see a circuit diagram of that machine: I have no idea what just happened here!

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