Home Forums Electronics Restoration How do I use a Eico signal generator to inject a signal Reply To: How do I use a Eico signal generator to inject a signal

#24249
Les Dickson
CVRS Member

Hi Dan. i’m not sure if you’ve received the information you need. The information below lists the steps in a generic troubleshooting a radio by injecting signal. I’ve found it quite useful.
Using Signal Generator to Troubleshoot Radios

  1. You should start your troubleshooting at the plate of the output tube.
  2. Start with the output of the generator turned up just enough to hear the signal with the volume at max on the radio.
  3. You will inject a 400 cycle AF signal into the plate of the output tube,
  4. then the grid of the output tube,
  5. then the plate of the first audio tube,
  6. then the grid of the first audio tube.
  7. If all is well up to this point, and the signal from the generator is heard in the speaker, set the generator to the IF (intermediate frequency) for the radio, usually 455kc. Inject this modulated signal into the plate of the last IF amp,
  8. then the grid of the last IF amp,
  9. and so on until you get to the front (antenna end) of the radio.
  10. Hearing the signal thru the speaker will indicate a normal condition, not hearing it places the trouble between where the signal was lost and the place you last heard it.
  11. You then measure voltages and resistance and figure out what the specific failed component is.
  12. The signal will get louder as you go toward the antenna, due to the additional stages of amplification.
  13. You will need to turn it down at each different test point if everything is working okay. You want to keep the output low during an alignment to keep the AVC system from affecting your alignment.
  14. Turning the output of the generator down during troubleshooting is not so important.
  15. The capacitor that you use with the signal generator hot lead is used to protect the signal generator from the DC power in the radio. The alignment instructions for the radio will tell what value cap to use, but I just leave a .01 at 630 on mine all the time, since that seems to be the most common value. If you use this cap at all times, you won’t damage the generator.
  16. Just as a reminder, PLEASE use an isolation transformer when you work on this radio. Not only will that protect you from harm, but it will be added protection against accidentally frying your generator.