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How to Test if an IF Transformer Is Good or Bad in an Antique Radio

If you have an antique radio that doesn't work, and you suspect a bad IF (intermediate frequency) transformer, you have your work cut out for you. Finding the test equipment you need may be a challenge, as you must generate a 455 kHz signal. Also you need skill to read the schematic diagram to identify the IF transformers (there may be three or more). You also need the ability to set up and use the test equipment, and the mechanical skill to open the radio housing without specific instructions.

Things You'll Need

Technician's hand tools
Schematic diagram of your radio
IF signal generator, capable of generating 455 kHz
Oscilloscope capable of reading 455 kHz

Instructions

- 1
  Open the radio to expose the components. Make sure it is unplugged.
- 2
  Read the schematic diagram to find the IF circuits. The reference from antiqueradio.org shows a schematic with a two-tube IF section with three IF transformers, one at the input of the first tube (1st IF), one between the two and one at the output of the second IF tube (2nd IF).
- 3
  Set up the signal generator to produce a 455 kHz signal and apply it across the primary of the first IF transformer.
- 4
  Set up the oscilloscope to read the 455 kHz signal and connect it to the output of the signal generator. This tests the signal generator and gives you an example of what the signal should look like at the output of the transformer.
- 5
  Connect the oscilloscope to the secondary windings of the IF transformer. The signal should look pretty much like the signal in the previous step, as a good transformer would not attenuate or distort the signal. If the signal does not appear or is distorted, the transformer is bad.
- 6
  Repeat the process for the other two IF transformers.

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