I Need Help - AI Part 11

Prompt: More corrections: there are no cast or aluminum chassis parts. Everything is heavy gauge galvanized steel. As you noted before, the Antenna Trimmer (C6) is located in the 1st RF compartment (closest to the rear of the radio) but is not used on bands 1 and 2. The frontmost compartment is the local oscillator

You are entirely right, and I need to stop leaning on memories of other gear and stick strictly to the actual anatomy of the SX-28. Thank you for keeping me honest.

The SX-28 does not use a cast aluminum chassis; it is built on that massive, heavy‐gauge cadmium‐plated/galvanized steel chassis with steel partition walls dividing the RF boxes. Furthermore, your correction on the compartment layout is exactly right: Hallicrafters laid the RF deck out with the 1st RF stage at the very rear (closest to the antenna terminals) and the Local Oscillator at the very front (closest to the front panel and main tuning dial).

Let's ground this entirely in the actual steel layout you are looking at underneath the radio, specifically for **Band 1**, where your front-panel Antenna Trimmer ($C_6$) is out of the circuit.

Testing the Tracking Limit at 600 kHz

Given that your oscillator compartment is at the very front of the chassis, the **Band 1 Oscillator Padder** screw is located in that frontmost section.

Because you are supplying a precise microvolt signal from your OWON generator, we can figure out exactly if the 7 KHz IF shift is what's choking the radio down to $35 µV:

1. Set your generator to exactly **600 KHz** with modulation.

2. Tune the SX-28 dial to **600 KHz**.

3. Locate the Band 1 padder screw in that frontmost oscillator compartment.

4. Turn that padder slowly through its range while listening to the audio or watching an AC voltmeter across the speaker terminals.

The Diagnostic Verdict:

Scenario A (It Peaks):

If you can turn the padder screw and find a definitive "sweet spot" where the signal peaks and then drops off on either side of the adjustment, then your oscillator is successfully tracking with the $462 KHz IF at the low end of the dial. If it peaks but the radio is *still* deaf ($35\mu\text{V}$), the tracking isn't your primary issue—you likely have an open primary winding on the Band 1 antenna coil (rear compartment) or a bad component in the 2nd RF/Mixer stages.

Scenario B (It Bottoms Out):

If you turn the padder screw all the way in (tight) or all the way out, and the signal just keeps getting louder right up until the mechanical limit of the screw without ever passing through a peak, **the $7 KHz shift has exhausted the adjustment range.** The radio is blind at 600 KHz because the steel-shielded oscillator coil cannot be tuned far enough to match the new IF gap.

When you rock that frontmost padder screw at 600 KHz, does it find a true peak, or does it run out of threads/tighten completely down?

Page: /1_need_help/Gemini_11/Gemini_11.shtml

Last modified: Tuesday, 21 Jul 2026