Antenna Switchboard Not Switching

 

I'm having a strange problem. It's probably something simple. The switching only happens on the 7473 on pin 13. the switching on pin 12 stays on. Measuring the voltage out on the pins of the 7473 I'm getting a difference of .6 vdc on pin 13, but only .3vdc on pin 12. The actual voltages are 3.8 to 4.4 on pin 13 but only 3.8 to 4.1 on pin 12. Looking at the schematic the only difference I can see is that I tied both protection diodes on the collector side with the 330 ohm resistors. Any thoughts?

 

Thank you

 

The 7473 is a NTE. I built a test circuit and found the the flip flop works with just LEDs on pins 12 and 13. In the antenna circuit pin 13 switches but pin 12 stays high. The voltage variation that I was seeing on pin 12 was only a drop in voltage when pin 13 switches on. I used zener diodes for the protection diodes, do you think that they could be the problem?

 

The voltage at the collector of the two transistors is also different, the tansistor connected to pin 13 goes to zero when switched off but the other on pin 12 never changes it stays high. I also tried changing transistors but there was no difference.

 

I also tried a 74LS73 and strangely the problem reversed, pin 12 switches and pin 13 stays high. Very frustrating. I used sockets for the ICs so I could change them if necessary.

 

Thank you for your help,

 

Dan

 

I just added the transistors to the test circuit and I have the same problem. When I drive the LEDs off pins 12 and 13 it works, but when I add the transistors it no longer switches. I'm using Radio Shack PNP Transistors part #276-2023 which are listed as General purpose medium power switching and small signal amplification.

 

Thank you,

 

Dan

 

I have not used any diodes in the test circuit. I'm going to Radio Shack and pick up some as well as some other transistors.

 

Thanks,

 

Dan

 

I connected the LEDs to the collectors of the transistors. The bases are connected to pins 12 and 13 and the emmiters are connected to +5vdc. The LEDs have the annodes connected to the collectors of the transistors and the cathodes connected to 330 ohm resistors to ground. The LEDs light but do not switch.

 

Thank you,

 

Dan