Bolex 18-5 problem

[Paul Coats]

Hello knowledgeable souls,
bought the above projector from the Evilbay Looked as new. Plugged it in. The breaker tripped when I flipped the switch. Could some helpful person walk me through testing? I have a digital multimeter, but have never used it😛

[Brian Fretwell]

The first thing I would suggest is to set the meter to resistance (Ohms) and test between Earth and Live then Earth and Neutral on the plug, if there is not a high reading there is a short circuit somewhere. If you are lucky this could be in the lead or the wiring in the plug either end if fitted. If there is a projector end plug unplug it and check Live to Neutral too. Check inside the plug(s) first as a stray strand of cable can cause this removing any stray wire will at least stop the breaker flipping. An old lead with rotting insulation can do the same and a rewire would be necessary.
If not I'll leave any recommendations to those who know the projector.

[Jon Byler]

it's possible that the primary on the transformer is shorted out, or there is a wire with bad insulation as brian suggested. To use the multi-meter, set to resistance/ohms. Think about things in terms of a circle... hence "circuit". there is a small voltage on the leads of your multi-meter when set to measure resistance, and when the circuit is completed, it will give a reading. with the two probes tips touching each other, you should get close to zero ohms. depending on the meter you have, it may be auto-ranging, or it may have manual range settings. if the probes are apart, it should read something like "OL" or ∞ (infinity). Your meter may also have a setting for checking continuity, where when the resistance is low it makes a tone. this is the easiest to use for what you need to check out.

if you measure and get very low resistance 0-1Ω it is showing that there is continuity along some path such as a wire. unplug the cord from the wall and the projector. never make resistance measurements on a live circuit! now check the resistance across the two main pins that go into the wall. if all is well, it should be ∞. if your cord has a ground wire in addition to Hot and neutral, check resistance between the ground pin on the plug and each of the other pins. should read infinity or whatever "open circuit" is on your meter. Finally, we check from one of the pins that is supposed to plug into the wall, and the various holes in the end of the connector that goes into the projector. only one of these should show very low resistance with each pin. if you get anything more than 1ohm (should be much less but your meter may not read much lower), there is a poor connection, or the wire is broken somewhere. given the problem you are having with circuit breakers tripping, I don't expect this will be an issue, but always good to look everything over.

Next step is to measure between the two power pins on the receptacle in the back of the projector where the power cord plugs in. I'm not sure what it should measure, as I don't know if the power switch switches the mains directly, or it it switches only the secondaries. I have a bunch of these projectors, so can check for you later tonight and see what it should be. All the same, there should be some resistance across the primary of the transformer, as there needs to be a fair number of coils of wire on the transformer to make it function well. it may be around 20Ω. it may read open circuit also, depending on where the switch is located in the circuit. if you switch to one of the run positions, it may change from open circuit/∞ to something like 20-100Ω or so. If you get a really low number when measuring the primary resistane, it likely means that there is a short in the machine, either the wiring to itself, or to ground, or inside the transformer.

Check the fuse on the machine, and see if it is still good. unlikely the fuse is causing a short to ground, but if the circuit breaker trips, the fuse should also blow. Look around in the machine and look for signs of sparking or burning.