Yaesu FT-757GX - Restoration - Episode 2: S-meter Illumination and Main Dial VFO Encoder Replacement

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This series is a master class reporting the restoration and tuning of a HF multi-mode and multi-band transceiver, the venerable Yaesu (Sommerkamp) FT-757GX. Two episodes will be released per week.

Released in the early 1980's, it features CPU-controlled PLL frequency synthesis for general coverage in the range 0.5-30 MHz. It has SSB, AM, FM and CW (with automatic keyer) modes. To mitigate interference in AM and SSB, it has IF shift and width controls that allow to continuously change the IF bandwidth, and also a noise blanker to suppress impulsive noises. Other features include 8 memories, 2 VFOs, receive pre-amplifier, receive attenuator, 2-speed AGC, speech processor and all-mode squelch.

Summary of the contents of the series:

Episode 1: Initial testing, disassembly and PA board cleaning.

Episode 2: S-meter illumination and main dial encoder replacement.

Episode 3: Heat-sink and cover painting. Reassembly.

Episode 4: Studying the block diagram and signal paths as a preparation for the alignment. Transmission, reception and control signals. SSB, FM, AM and CW.

Episode 5: PA, LPF and Local Unit Alignment (1/5) - Final transistor bias adjustment, CM coupler balance, third local oscillator bandpass filter, local oscillator level, 45 MHz bandpass filter, 60 MHz bandpass filter.

Episode 6: Local Unit Alignment (2/5) - 45 MHz tripler, 15 MHz reference frequency, 2nd local oscillator frequency, carrier point.

Episode 7: Local Unit Alignment (3/5) - BFO frequency AM/FM carrier frequency, carrier level, carrier balance, AM carrier level, PLL subloop VCV.

Episode 8: Local Unit Alignment (4/5) - 41 and 56 MHz bandpass filters, main PLL VCV, 2nd local level.

Episode 9: Local Unit Alignment (5/5) - IF shift zero point set, VOX gain preset, SSB carrier point check, FM modulation.

Episode 10: RF Unit Alignment: Receiver Circuits - 3rd local buffer, 2nd local buffer, width oscillator, RX IF transformers, IF gain and S-meter sensitivity, noise blanker, FM 3rd local level, squelch threshold, FM RX AF output level.

Episode 11: RF Unit Alignment: Transmitter Circuits - ALC meter zero set, TX IF transformers, TX power, PO meter, SWR turndown (AFP), CW sidetone level.

Episode 12: Bench Testing: Output Power, Reception Sensitivity and Frequency Stability.

Episode 13: Showcasing and On-The-Air Testing with a contact (QSO).

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