Yaesu FRG-7700

The FRG-7700 is a compact communications receiver for AM, SSB (USB/LSB), CW, and FM from 150 kHz to 30 MHz. Sensitive, stable, pleasant audio — no menu maze; tune band and mode and listen. Still popular after 20+ years.

Buy carefully on the internet — many “good condition” listings arrive as junk. If you cannot inspect and pay cash locally, save your money.

Market debut 1981; replaced by FRG-8800 in 1986. Early units used a felt ring on the frequency scale coupling; later units used a spring.

Serial format example: 4E 290421 = May 1984 (first digit = year, letter = month A=Jan…, then production run + serial). Also seen: 1F 070507 (June 1981), M1C 050492 (March 1981, memory module), 1E 060340 (May 1981).

User and service manuals are essential for alignment and repair — see the Fox Tango manual library. Also useful: mods.dk (limit 2 manuals/day).

Spare parts are scarce after 20+ years, but most components are standard. Mechanical switches and controls are the hard parts — watch hamfests and the Fox Tango graveyard section. Rugged design; failures are often amateur-induced.

After decades, re-alignment may be needed. Each band normally overlaps ~30–50 kHz at each end (e.g. 7 MHz band tunes ~6950–8050 kHz).

PLL symptoms

• High end of every MHz range drops (analog scale stops ~950) → re-align first PLL
• Only 5, 12, 20, 29 MHz band ends low → re-align second PLL

Reference oscillator (manual correction)

MR switch OFF. Connect counter to TP04 (not IC pin 9). Adjust TC2002 for exactly 6.400 MHz.

First PLL

DC VTVM on TP05. Dial at “1000” → adjust T2007 for 7.0 V. At “0” expect ~2.4 V (manual says 1.5–2.0 V; PA0PGA finds 2.25–3.1 V OK on working sets).

Second PLL

VTVM on TP03. Dial at “1000”: 5 MHz → T2004 = 7.4 V; 12 MHz → T2003 = 7.4 V; 20 MHz → T2002 = 7.4 V; 29 MHz → T2001 = 7.0 V. At dial “0” on 0, 6, 13, 21 MHz bands: 1.5–2.0 V at TP03.

Coil cores are wax-stabilized — be gentle. If a slot breaks, flip the core upside down for a second try. Cores are not interchangeable — do one at a time.

Power supply

Transformer, bridge, and 6800 μF/40 V cap stay powered for clock/timer — rectifier runs hot; solder joints can crater; one set had transformer wires burn. Check bridge joints or substitute 4× 1N5405. Add rear power switch if unused for long periods. Use backup battery adapter with memory option.

Dial lamps

12 V / 100 mA with long leads. VFO lamp is glued to grommet — remove power cord first before front-panel work or you risk destroying the always-on counter IC.

MSM-5524RS display driver

40-pin OKI LSI — clock, timers, 5-digit counter driving FIP 5A8B fluorescent display. Same IC as Kenwood R-1000. Obsolete and scarce (~$60 used on eBay). Common failures: VFO lamp short, bad mode switch, corroded diodes D42/D43/D44 (yacht salt spray). Replace bad diodes with 1N4448.

Display shows PLL frequency offset by 455 kHz IF. SSB will read ~1.5 kHz off carrier; resolution is 1 kHz.

Display tube FIP 5A8B

Green VLF tube with amber Yaesu filter. Dim display? Removing filter brightens green temporarily — most restore the filter for the classic Frog look.

AM band & cosmetics

Under 2 MHz sensitivity is weak compared to boat anchors like the R-390A. Front paint scratches easily (metallic spray on plastic). Hammerite white for knob markings; automobile wax on crinkle-finish covers.

A spare receiver with blown PSU board but good transformer → custom LM-317 + NPN supply (11 V adjustable, runs cooler). PLL board had pulled traces, bad MC14504 level translator, broken VFO connector wire, solder bridge between USB/LSB oscillators, shorted counter amp transistor, failed D43 diode (5 kΩ!), rusted S-meter swapped for cassette-deck VU meter.

After tune-up, sensitivity matched other FRG-7700 units. Use IC sockets when replacing 40-pin packages.

Fine tuning (RIT-style)

Without memory module, use pin 13 of plug P34 (white/violet wire) — same voltage as memory fine tune. Add BB209 varicap + 12 pF NP0 cap across VFO tuning capacitor. Tune range ~12 kHz on low bands, ~3–4 kHz high — enough for ham nets. Reversible if you add memory module later.

Georg Lechner mods (via dr-boesch.ch)

Originally in Weltweit Horen 11/1986. Re-align after receiver-board mods:

1. 100–200 μH choke across SW socket; ~1 mH across BC socket (DC path)
2. R3: 47 Ω → 470 Ω (better attenuator)
3. Remove R01 (4k7) and R03 (470 Ω) — decouple BC/SW inputs
4. C07: 47 nF → 4n7; C69: 10 nF → 2n2
5. R46: 470 Ω → 330 Ω + 500 μH–1 mH choke in series (Q1–Q6)
6. R60, R61, R76, R78: 470 Ω → 330 Ω
7. R79: 100 Ω → 100–300 μH choke
8. C94, C95: 10 nF → 1 nF; remove R85 (4k7) — re-align T09/T10
9. C89, C101, C111, C117: 10 nF → 560 pF
10. Remove R65 (12k), R124 (10k) — do not remove R115 (oscillation risk)
11. Optional IF filter upgrades: CF01 CFW455HT; CF02 CFJ455k6; CF03 CFS455J; CF04 CFS455H6
12. C164: 470 μF → 47 μF (audio — PA0PGA preferred 150 μF)
13. C158: add 330 nF parallel (PA0PGA used 270 nF instead)