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Fujitsu FES-1, FES-2 and FES-3

Contents

Overview

FES-1, FES-2 and FES-3 appear to be Fujitsu’s original reed keyboard switch design, using Fujitsu FDR-7 reed capsules.

FES-1 and FES-2 were documented in the Fujitsu magazine in 1970, in volume 21 number 4 article FES-1および2形押しボタンスイッチ/Pushbutton Switches, FES-1 and FES-2 by Yuzo Sato (佐藤雄三), Ryohei Kinoshita (木下良平) and Noriyuki Ukai (鵜飼規之), pages 657 to 667. This article, almost entirely in Japanese, describes the design and operation of the switch. The article was provided by Kiyoto and cannot be posted online.

FES-2 is the illuminated version of FES-1, and appears to be designed for control panels rather than keyboards. Both series were available in momentary and alternate action forms, and FES-2 also appears to been sold in indicator form (lamp only, with no reed capsule fitted). These are tall reed switches, with a plastic shell and a metal plate retention clip.

These switches were rediscovered by UncleFan when he found keyboard N860-1131-T010 for sale on Taobao Idle Fish, and Kiyoto found that it had previously been posted to the Baidu forum. The FES-1 switch designation was hypothesised from the keyboard model number (N860-1* originally indicating FES-1) and this was later confirmed following research into Fujitsu literature. The keyboard itself is from November 1984. Only one switch part number can be seen in that keyboard: 121954.

FES-3 is mentioned in a 1979 article; an exploded illustration of FES-1 is captioned simply “適用製品名:FES-1,2,3形押釦スイッチ” (“Applicable product name: FES-1, 2, 3 pushbutton switch”) and no other mention of FES-3 is made. The expansion of the term “FES” is also not given.

Family

Series Description
FES-1 Non-illuminated keyboard pushbutton, momentary and alternate action
FES-2 Illuminated pushbutton, momentary and alternate action
FES-3 Not observed or documented

Design

FES-1 and FES-2 are tall reed switches, with a flat metal dual-prong keystem very similar to that of IBM beam spring. Fujitsu were aware of IBM’s products, as the later FES-5 from 1972 was intended to mimic the IBM Selectric just as IBM’s own beam spring was, and the FES-8 article cited IBM beam spring (in pictorial form only, with no explicit reference to IBM) as one of the prior examples of a tactile switch, along since Micro Switch SD and FES-5. The switches are secured to the mounting plate by way of sheet metal clips affixed to the switch. These mounting clips may have been optional, as they had their own part number in 1984.

Single and double pole configurations were offered. Double-pole switches could be either 2 form A, or 1 form A plus 1 form B. FES-2 switches have two lamp sockets, and by default these are supplied with a pair of 5 volt, 60 milliamp miniature bulbs. Additional bulb ratings were available for ordering separately, with the switch thus ordered without lamps fitted.

Both downstroke and upstroke damping is provided by way of rubber mats.

The alternate action mechanism is placed onto the outside of the switch. A slot down the side of the switch allows the plunger to connect to the latching arm. This moves within a typical heart-cam track, itself in a plastic block that is attached to the switch shell when required. (In the same issue of Fujitsu magazine—vol. 21 no. 4 from 1970—Fujitsu had depicted a star wheel mechanism in their F 3300 pushbutton series, similar to what Cherry introduced around the same time with M6 alternate action.)

The design of the switch as found in keyboard model N860-1131-T010 from 1984 is noticeably different from the design as shown in the Fujitsu magazine in 1970. It is not possible to be quite sure what has changed without examining a loose switch. The drawing below depicts the switch as originally designed; this drawing is a combination of several Fujitsu drawings, as none of them are complete or accurate enough to get a precise understanding of the dimensions, and they are not consistent with each other.

Specifications

The following specifications were given in the Fujitsu magazine:

Property Subseries
FES-1N FES-1L FES-2N FES-2L
Operating force (max) 150 g 300 g 150 g 300 g
Bounce time (max) 600 µs
Travel 3.5 mm 5 mm
Contact resistance (initial) 200 mΩ max
Lifespan (max) 10⁶ 10⁵ 10⁶ 10⁵

The lifespan figures are surprisingly low considering that these are reed switches, but this is not wholly unexpected for that era.

Parts

Part numbers

The Fujitsu magazine details the part number format for the switches, display units and components. The following sub-classifications are defined:

Prefix Subclass
FES-1N FES-1 momentary switches
FES-1L FES-1 alternate action switches
FES-2N FES-2 momentary switches
FES-2L FES-2 alternate action switches
FES-2T FES-2 display units
FES-2P FES-2 individual parts (FES-1P may also exist)

Switches

Switch part numbers take the following format:

FES-NFC(L)

N
Series: 1 = FES-1 non-illuminated pushbutton, 2 = FES-2 illuminated pushbutton
F
Function: N = momentary (“non-lock”), L = alternate action (“lock”)
C
Contact configuration: 1 = SPST-NO, 2 = DPST-NO, 5 = DPST-NO-NC
L
Lamp type (FES-2 only): 1 = 5 V, 60 mA (omit this position when a different lamp type is required)

Display units

“Display”/“display unit” (表示) refers to the specialist relegendable keycaps used on illuminated switches. For now it is assumed that these are FES-2 only, because they would make no sense as FES-1 parts. Display unit part numbers take the following format:

FES-2TFDC

“T”
Display unit part
F
Form: 1 = Type-1, 2 = Type-2, 3 = Type-3
D
Division: 0 = not split (分割しない場合)
C
Colour: 1 = translucent white, 2 = red, 3 = yellow, 4 = green

“Division” likely means a keycap with two colours side by side, each lit by one of the two lamps. There are no details given on codes for divided keycaps.

The three types of display unit are illustrated in the Fujitsu magazine (vol. 21 no. 4, 1970, page 663). Types 1 and 2 are taller and appear to permit both lamps to light the same legend. Type 1 has a colourless transparent nameplate, while type 2 has a translucent white nameplate. Type 3 is shorter and appears to divide the illumination into two halves, one half per lamp, allowing two separate legends on two separate colour backgrounds to be lit independently. It is hard to be clear on this without transcribing and translating the entire page of Japanese text.

Components

Fujitsu did not indicate whether component part numbers apply to FES-1 as well as FES-2. In all but one instance, the codes appear to be specific to illuminated switches. The following components are documented:

Prefix Subclass
FES-2P120 Name plate (colorless transparent)
FES-2P220 Name plate (translucent white)
FES-2P761 “Stop spring” (止めばね); this may also exist as FES-1P761
FES-2P980 5 V 60 mA lamp
FES-2P981 5 V 115 mA lamp
FES-2P982 12 V 60 mA lamp
FES-2P990 Display removal tool
FES-2P991 Lamp socket extraction tool

Numeric part codes

In the only instance of these switches being observed, they are stamped with part numbers and date or batch codes in the same format as the codes found on FES-8 and FES-9 switches. The format of these part numbers is not known.

Part number Part Found in
121954 Unconfirmed momentary model N860-1131-T010 (1984)
121957 Switch retention clip N860-1131-T010 (1984)