BulbDial red ring problem

[karlkonnerth]

My blue and green rings work fine.  However, none of the LEDs on the red ring light.  What should the voltage be on the connections LED 6 and 10?  When I go to what should be test 6, LED 6 is -1.64 and LED 10 is  about -1.8.  Any suggestions?
Thanks.   Karl

[Windell Oskay]

There should not be any negative voltage anywhere. So, you may not be measuring what you think you’re measuring. And in any case, there is not a DC voltage that can be measured there; it’s an oscillating signal that you can view with an oscilloscope, but the “DC voltage” that you measure will depend upon several factors including the type of meter that you use.

All of the red LEDs are connected to the LED10 line.  So, check that line carefully, both at resistor R10 on the main (blue) circuit board, and its connections on the red ring. Make sure that it’s not accidentally connected (electrically) to something that it shouldn’t be, and that there is actually a connection from R10 to the ring.

[karlkonnerth]

I checked all of the connections on the LED10 line and they all looked good.  I then re-soldered them to be sure.  Still none of the red LEDs light.

I don’t have a scope handy at the moment.  If I get one, what should I expect the signal to look like on this line?

I made the voltage measurements to what I believe is ground using a Fluke 8020A multimeter.

Any other suggestions?
Thanks.   Karl

[Windell Oskay]

In general, it’s a bad idea to re-solder connections unless you have a specific reason to do so.  We’ve seen quite a few boards destroyed by unnecessary re-soldering. 

You can use your multimeter (with the Bulbdial unplugged) to check the resistance between the different lines. Look at the circuit diagram, and make sure that (for example) the resistance from pin 16 of the chip to control line LED10 is 68 ohms, and that the resistance from pin 15 to LED 8 is 24 ohms. Also make sure that there is high resistance between any two of the signal lines that go to the red board.

[karlkonnerth]

I am somewhat confused by your comments.  The circuit diagram shows pin 15 (not 16) connected to the 68 ohm resistor which connects to control line LED 10.  It shows pin 16 connected to the 24 ohm resistor which goes to control line LED 1.

[Windell Oskay]

Looks like you’re more on top of this than I am! Yes– do what the diagram says, not what I say. ;)

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