Trouble with "SIMPLE TALK AND CONTINUITY TESTER"

[davidbholcomb]

I had fun building the "SIMPLE TALK AND CONTINUITY TESTER" found on the oldphoneguy.net website. It works perfect for testing the transmitters and receivers of my phones but for some reason the led does not flash when I try to test the rotary dials. However on my magneto phones it flashes quit well when the mag is turned. What might I have done wrong or am overlooking? Did I get the wrong led, I am using a led rated 2.4V, 20mA

[HowardPgh]

Please don't take this wrong, are you connecting to the proper connections on the dials?    Y-Bk for pulse on #5 and 6 type dials. At rest BB-W show continuity and Bk-R are open.  Green and Blue wires on most dials in 500 type phones.  The white wires are the shunt/mute contacts and show continuity when the dial is turned.
Or there may be a problem with the dial you are testing, and make sure your test leads aren't touching each other as thins are close together inside phones.
Howard

[davidbholcomb]

Hi Howard,
I make myself feel like a dummy, I spent the better part of yesterday trying to figure out what was wrong with my Princess and in the end only one wire needed to be moved and it was in the schematic that I had looked at for hours!

On the oldphoneguy site I was under the impression that I could hook this "STCT" up to tip and ring(this is what I have tried with known working phones) and when I dialed the led would flash. Is this wrong?

If I can get this to work it will be a really neat thing to take along and check phones at garage sales and swap meets.

[HowardPgh]

Dave- I think it should flash if you hook it up to a normal phone via L1 and L2.
If you take it to the Flea market and garge sales, test the phones secretly or you will lose a bargaining point, because the seller will know that the phone works.-Howard
Be careful testing a magneto phone-you may burn out the LED when you turn the crank.

[davidbholcomb]

Thanks for the help Howard. I finally gave up and started over. I was using a 1/4 w 330 ohm resister and a 2.4V, 20mA LED. I reconstructed with a 1/2 w 330 ohm resister and a 1.7V, 20mA LED and the device works like a jewel.

With success I discovered a quick check to see if the device is working, simply connect the 2 ends and the LED should light. This is something my first attempt did not do even though it worked for testing the receivers and transmitters. It did flash when I used it on the magneto but never burned out. I must of had a LED that required too much power.

I will be sure to be sneaky at the garage sales and such.

[Bill]

Dave -

As Howard pointed out, I'm surprised you got away with cranking the magneto directly into the device. Magneto voltages can be pretty high, and LEDs hate high reverse voltage.    BUT!   Since you now have an extra LED lying around, you can make your STCT reasonably burnout proof simply by connecting the extra LED directly across the LED that is already in the device - but connect it backward. Each LED will protect the other from overvoltage. The fact that they have slightly different ratings doesn't matter.

Bill

[davidbholcomb]

Dave -

As Howard pointed out, I'm surprised you got away with cranking the magneto directly into the device. Magneto voltages can be pretty high, and LEDs hate high reverse voltage.    BUT!   Since you now have an extra LED lying around, you can make your STCT reasonably burnout proof simply by connecting the extra LED directly across the LED that is already in the device - but connect it backward. Each LED will protect the other from overvoltage. The fact that they have slightly different ratings doesn't matter.

Bill

Bill

Hi Bill, thanks for the response. I had no idea what you were talking about so I studied it for awhile when all of sudden I realized something...now that I have stopped laughing at myself and can share, I now know what was the problem. I am not very knowledgeable about electrical engineering. I had no idea why the oldphoneguy plans called for a long lead and a short lead. It made no sense to me, I thought, why would there need to be longer wire on one side of the LED than the other. You are all probably laughing your heads off right now, it took me awhile to stop, but I had no idea that LED's had to be installed in a correct direction. That one side is positive and the other negative. Now you know why schematics drive  me  nuts. I am learning as I go. Believe it or not I am having fun. So the problem was I installed the LED backwards! The next time I just got lucky and installed it the proper way. (50/50 chance)
I know nothing and I can prove it!

[twocvbloke]

Might be handy to print out this image of the construction of an LED...