1V Gen. Illum. Circuit Question

[sudsy7]

On the I/O board schematic, it appears the 1v gen'l illum. circuit (wire code 30) ties directly into the 7.5v circuit (wire code 20).  I'm not an electrical type, but how does that work?  Seems like it should go to ground (wire code 90) to complete the circuit.

[rokgpsman]

Looks to me like the General Illumination lamps on wire code 30 are attached to the 7.5vac power. They probably get their ground return thru the metal mounting base of the lamp or from another ground wire that gets connected to wire code 90 (if 90 is a ground circuit, can't tell about this since the schematic you show is just a portion). These lamps would come on as soon as the machine was powered up and operate from the 7.5vac. If you look at one of the Gen Illum lamps you will see how it receives power and you can measure it at the lamp to verify it is 7.5vac. If there is only one wire connected to the lamp then the ground connection is thru the mount.

What makes you think that wire code 30 and the Gen Illum lamps is a "1v" circuit?

[sudsy7]

What makes you think that wire code 30 and the Gen Illum lamps is a "1v" circuit?

Thanks for the reply, rokgpsman.  Here's a couple of more excerpts from the electrical schematics that show that wire 30 is 1v and wire 90 is ground. 

[rokgpsman]

Those extra portions of the schematic show that you are right, wire code 30 is a 1 vac circuit, thanks for posting the additional info.

Here's what happens: The Gen Illum lamp circuit is connected to the 7.5 vac on one side of the lamp and the other side is connected to 1 vac (instead of ground). This gives a voltage difference of 6.5 vac to the lamps and the lamps work just fine using 6.5 vac. Wire code 20 is 7.5 vac when measured to ground and wire code 30 is 1 vac when measured to ground. But between them there is 6.5 vac difference. If you measured the voltage at the lamp socket on the two wires going to it your meter would read 6.5 vac since your meter lead low side reference would be 1 vac, not ground which is zero. But if you measured the high side voltage with respect to ground it would read 7.5 vac. But again, your Gen Illum lamps only see the voltage difference between the 2 wires connected to them.

Electrical current flows thru a lamp (or other device) when there is a voltage difference applied to it. We normally think of this as flowing from some voltage to the lamp and then to ground. But since electricity can flow anytime there is a difference of potential then the low side does not necessarily have to be ground, it can also be any voltage that is lower than the source voltage.   

In this case the low side of the circuit is 1 vac instead of ground. To the lamp it sees the 6.5 vac voltage difference between its 2 connections. You could connect 100.5 vac to the lamp on one wire and 94 vac to the other side and still the lamp would only see 6.5 vac and work just fine.

The design in this machine used 1 vac as the low side for the General Illum circuit. The 1v wire is not the source voltage, it is the return path. You can think of it as a return line in a similar way as a ground wire would be. This means the Gen Illum circuit is a 6.5 vac circuit, not a 1v circuit. The 10 amp fuse for the Gen Illum circuit is in the 1v wire going to the lamps, which can be confusing and make one think the 1v wire is the voltage source.

I hope my comment explains it well enough, if not maybe others can clear things up.

[sudsy7]

Great explanation - it all makes sense.  I just don't understand what the benefit of using the 1v winding as a return path was for the designers.  I would have thought it would have been easier to just make a separate 6.5v winding.  I'm guessing it has something to do with cost savings (less windings on the transformer).  But then that makes me wonder why they just didn't eliminate the 1v tap altogether and just use the 7.5v circuit for the gen'l illumination.  Maybe the bulbs would be too bright and/or have to be replaced too often?  Anyway, I'm sure they had good reason.   

Thank you for explaining this so well and taking some of the mystery out of it for me!

[rokgpsman]

Great explanation - it all makes sense.  I just don't understand what the benefit of using the 1v winding as a return path was for the designers.  I would have thought it would have been easier to just make a separate 6.5v winding.  I'm guessing it has something to do with cost savings (less windings on the transformer).  But then that makes me wonder why they just didn't eliminate the 1v tap altogether and just use the 7.5v circuit for the gen'l illumination.  Maybe the bulbs would be too bright and/or have to be replaced too often?  Anyway, I'm sure they had good reason.   

Thank you for explaining this so well and taking some of the mystery out of it for me!

I had very close to the same thoughts as you, why go to the trouble to add the 1v winding when they could have added a 6.5v winding instead and just connected the lamps between 6.5v and ground.  An idea that came to me, on some early machines that have sound they wanted to avoid 60 hz audio hum in the sound circuits. By keeping the ac lighting off of the common ground circuit maybe it avoided the hum problem - just a guess.  Or maybe this machine already had a need for the 7.5v and the 1v voltages elsewhere so they used them for the lamps too.

Those lamps are probably the more common 6.3vac lamps, right? But even if they are 6.5v lamps if they had run them off the 7.5v and ground that would have created more heat and shorter bulb life, as you say. I trust the elec engineers and feel that there is a solid explanation for doing it this way, even if I don't know the answer myself.

Is this a common way to do the lighting on Bally machines of your machines age?

[sudsy7]

I think all the controlled lamps are #47's and the gen'l illumination lamps are #63's.  There aren't too many gen'l illumination lamps in my machine though - I think just some above the coin trough only.  Most of what I would call gen'l illumination is done by fluorescent lights.

This is the only slot machine I own, but I believe all the 80's E-series gen'l illumination is wired in this manner.  I do have several pinball machines dating back from the 60's thru the 90's, and I have never seen a 1v circuit like this in any of them - that's what made me curious about it.   

[rokgpsman]

I believe the #47 lamps are 6.3v and the #63 are 7v lamps.

Those #63 lamps use a little over 4 watts each, so they do get hot. The #47 ones are much lower, just under 1 watt.

[The Fatman]

Thanks for that info too. I swap out my regular 44 or 47 and 63 lamps with LED bulbs. They are cooler, can be brighter, and wont effect the paint on the glass as much as the others. Operate very cool with less juice too. I am wondering if the transformers were made for another product and Bally instead of having a whole new one made just for them, they could use the pre-existing one and save $$.
Dave F

[rokgpsman]

Yes, LED's are definitely cooler and pretty much last indefinitely, although some report they can start giving a yellowish cast to the light after many many hours of use. But that could have been with older generation LED's.

And even just removing the #44 lamps and installing the #47 in their place will save on heat and elec use, the #47 uses about 40% less electricity. You will get a little less brightness but most people find it worthwhile to protect the glass artwork and nearby plastics from heat damage. If #44 lamps are used in the pushbuttons they can be changed to #47 lamps and reduce the heat aging to the plastic button cover.

That's a good point about Bally possibly using a transformer they already had in their stock system.