Proceed at Your Own Risk
This modification requires board work on your display unit. Test carefully and double-check wiring before reassembly. Fox Tango assumes no responsibility for damage to your equipment.
Introduction
The FR-101 is more than an amateur receiver — it tunes all major shortwave bands. It can be annoying when the display flashes while listening just outside the ham or shortwave bands.
A Fox Tango member wrote Yaesu in 1978 after an earlier newsletter incorrectly reported a Yaesu anti-flicker kit. There never was a kit — only a simple trace cut and wire to +5 V. You need a sharp knife or scalpel, a soldering station, and a small piece of insulated wire.
The Modification
Anti-Flickering Mod for FR-101 and Similar
Isolate pin 6 of Q3 (SN7400) by cutting the pad on the bottom of the board. Connect the pad (not pin 6) to the +5 V supply at pin 14 of Q3.
Disassembly
- Remove four screws holding the display — pull each screw halfway at a time so “C” clamps do not pop off.
- Unplug the yellow coaxial cable (RCA connector) from the side of the counter.
- Carefully remove the two multi-lead connectors — plastic clips on the black connectors break easily.
- Remove top and bottom covers of display board PB-1426A.
Board Work
- Locate IC Q3 (SN7400), just forward of the HC6/U crystal, running parallel with the rear of the counter.
- On the bottom of the board, cut the trace at pin 6 of Q3 — cut the trace in the middle of the chip, not at the pin itself.
- Run a small wire from the cut pad (center of chip) to pin 14 of Q3 — not to pin 6.
- Pin 14 has a 2.2K resistor in plastic cover going to +5 VDC.
- Inspect under magnification, reassemble, reconnect yellow coax (required for counting), tighten screws gently.
Without the mod, the display flashes above 7.5 MHz (e.g. 7.516 MHz reads steady after the mod). W4CLM planned to try the same mod on the YC-601 counter.
Replacement display lamp: Nixie-tube displays were available from Yaesu Anaheim as part G6090044 (as of Jan 2004) for YC-601 or FR-101 displays.
Step-by-Step Photos
Be careful when removing the counter — disconnect the yellow coaxial RCA cable and two black multi-lead connectors.
Steady Display
Without the flicker modification, the FR-101 and YC-601 display flashes once you go above 7.5 MHz. After the mod, you get a steady display.
All photos property of Fox Tango International & W4CLM.
VFD Display Tubes
Commonly known as VFD (“Digitrons”). The YC-601 digital display and FR-101D digital receiver of the mid-1970s use the NEC LD8062 and Futaba DG10S1. The LD8062 also appeared in early four-function calculators — a possible spare-parts source if supply dries up.
Futaba VFD DG10S1 — 10 mm full indicator, 8 mm numerals (0–9, comma, decimal). Found in the Yaesu FR-101D digital receiver display.
- Number height: 8 mm — diameter: 9 mm — height: 35 mm
- Base: 12-wire — nominal voltage: 15 V — cathode stream: 2.0 mA
Jan 2006 — Futaba Corporation re: VFD DG10S1:
“This is a VERY obsolete part… replacement parts just don’t exist. Check the power supply and drive signals first — VFDs are very robust unless broken or run 24/7 for decades.” — Nick Price, Senior VFD Engineer, Futaba Corporation of America