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Maxi-Switch

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Overview

The Maxi-Switch Company (later Maxi Switch Inc) was an American switch and keyboard manufacturer, known mostly for switch types that appear to be derivatives of products from other brands, but also for a distinctive type of plunger over rubber dome arrrangement. Barely any literature has survived, but a few details have been recovered. Maxi-Switch are also known for manufacturing a subset of IBM Model M keyboards in Mexico.

History

Maxi-Switch were at one stage owned by EECO (Electronic Engineering Company of California). They had a keyboard plant in Carborca, Mexico and a keyboard and switch business in Scotland, as well as a keypad manufacturing plant in Phoenix, Arizona. In May 1990, EECO filed for bankruptcy protection, and in July that year, the keyboard division was sold to Silitek of Taiwan. Silitek announced they would retain the Tucson, Arizona facility and rename it Maxi Switch Inc.

In December 1995, Maxi Switch “agreed to acquire the manufacturing rights, patents and assets for Lexmark International Inc.’s Select-Ease and Rubber Dome computer keyboards, including a patent for its Buckling Spring technology.”

Series

The only documented correspondence between a series name and PCB code is for the 2900 Series hexadecimal keyboard from 1977, whose PCB is marked 2903-014-02 and whose part number is 2129-011. Other keyboards with block reed switches have PCB codes that begin “29” and part numbers that begin “2129”, suggesting that the PCB code indicates the series name, and that the first two digits of the series name are the third and fourth digits of the part number.

An unidentified keyboard with some form of discrete switch has a PCB code 3101-090-02 and part number 2132-033. As Series 3100 is documented a mechanical switch type, this would seem to strengthen that PCB code theory. The fact that the part number begins “2131” instead of “2131” cannot be explained.

The rubber dome keyboards however are more confusing. Here, the part numbers typically begin “2186” (PCB) or “2189” (membrane) or “219”. This would suggest series 8600, 8900, 9100, 9200 etc, but it may be that they simply stopped using series names at this point.

Some series are confirmed from the 1973 Electronic Engineers Master advertisement.

Confirmed

The following series names are confirmed from literature.

Series 1600 and 1800

These are keystrip modules that can use reed capsules (28 V DC at 250 mA), cross-bar palladium contacts (3 A at 28 V DC or 115 V AC) and snap-action power contacts (only in Series 1600, 15 A at 250 V AC or 500 mA at 125 V DC). Series 1600 is 1.5″ high and Series 1800 is 1.1″ high. Key spacing can be 0.625″ or 0.75″.

Series 2700

Series 2700 was advertised as “pre-tested” reed switches, suggesting that the reed capsule is enclosed inside the switch.

Series 2900

Series 2900 comprises ganged reed blocks, with a reported lifetime of over 100 million operations and a 2.5 oz (around 70 g) operating force. The reed capsules can be individually replaced in the field through holes in the PCB. The plastic blocks house only the plungers, not the switch mechanism, which is soldered separately. This is the only confirmed series to date to be examined.

The reed blocks have a base to contain the return springs, and are secured to the PCB with screws and nuts. It appears that two nuts are placed onto each screw: one to hold the switch assembly together, and one to secure the assembly to the PCB.

Series 3100

Series 3100 is a mechanical switch type. It is described as having wiping contacts. In Electronic Design Vol. 21 No. 17 from 16th of August 1973, Series 3100 was stated as having “dual bifurcated gold contacts” and a lifetime of 10⁶ operations under load. Series 3100 encoded keyboards were said to cost as low as $50.

The unidentified keyboard 3101-090-02 listed below has switches marked “PAT.NO.” and a patent number ending “10,060”. The only US patent for a pushbutton switch from that era that ends with those digits is US 3710060A, filed in July by Bunker Ramo, and granted in January 1973. The patent is contemporary with the Maxi-Switch advertisement and the design fits: it has the side holes as seen in the photos and the dual bifurcated contacts (not for redundancy, but because it is double-break, or bridge contact) and the contact design appears to provide wiping motion. At no point was the patent ever assigned to either Maxi-Switch or EECO, however.

The Bunker Ramo design has additional contacts that press against the PCB to make its electrical connections, and is secured with a nut and screw. Maxi-Switch’s version has standard solder terminals.

Captron

Captron is a block foam pad capacitive series. The design is very similar to Series 2900. The modules lack the base found in Series 2900 and are open at the bottom so that the foam pad can reach the PCB; consequently the return spring is placed under the keycap instead. The sense pads on the PCB are curiously not protected by solder mask.

The PCB code suggests Series 4000, but in Electronic Design magazine in 1976 [ED1976-FOK] they are cited as Captron. The only known example is the Digital Group KEY-1 keyboard.

Unconfirmed

Series 6300

This is a hypothetical designation for what is known as “vintage linear”, a switch that is nearly identical to SMK J-M0404 series. The part numbers begin “2160” instead of the expected “2163”, so this could be Series 6000 instead. No advertisement has been found for these switches and keyboards.

Series 8000

Known only from “803861-001” listed by Radwell. It appears to be another strip type.

Elastic contact

These are identical in principle to Alps elastic contact, while using a shell derived from the “vintage linear” type. They are only known from the oldest TRS-80 Model 4 keyboards — see Maxi-Switch elastic contact illustration.

Rubber dome

Clear distinction between rubber dome families is not yet possible. Tentatively it appears that part numbers beginning “2186” indicate conductive domes over a PCB, while part numbers beginning “2189” indicate conductive domes over a single membrane sheet. As these keyboards are held to be of much less interest to anyone, disassembly photos are rare, which impedes understanding. This is muddied further by the aquisition by Silitek, as production was moved at least in part to Silitek’s factories, causing the adoption of Silitek’s own slider-less switch design into the Maxi Switch range.

For now, they are being treated separately but collectively.

Example keyboards

Mechanical, reed, capacitive

Note that some series names are hypothetical; see above for more details.

Series Description Examples
Keyboard PCB code Part number Date Country Serial
2900 Block reed Maxi Switch 2900 Series hexadecimal keyboard 2903-014-02 2129-011 372-507
MCM/900 keyboard 293079 2129-069 238 347
Unidentified keyboard 293103-06
3100 Discrete mechanical Unidentified keyboard 3101-090-02 2132-033 1111 456
Captron Block foam pad Digital Group KEY-1 keyboard 403003-04
6300 “Vintage linear” Cybernetic Data Products keyboard 630010-09 2160029 USA 1488-440
Unidentified keyboard 630010-10 2160029 1982-10-14 USA 5996
Commodore PET add-on keyboard 630011-03 2160010 749-199
Billings 6000 keyboard 630067-03 2160148 1983-04-22 USA 1123
Xerox 928-900451 630107-02 110S80577 2160132 1984-01-11 USA 016020
Geomet 200 KYBD 2160177 2160177 1984-07-24 1228

Rubber dome

Keyboard Part number or model Type Keycaps Date Country
Maxi-Switch ME 101 218603XXX Conductive dome, plungers, PCB Not depicted Unreadable in photo Unreadable in photo
Gateway 2000 AnyKey 2189014-00-211 Conductive dome, plungers, single membrane Double-shot 1992-01-?? Mexico
Unidentified internals 2189XXX-XX Conductive dome, plungers, single membrane 1995 week 23
Maxi Switch 2192004-XX-XXX 2192004-00-001 Silitek rubber dome over membrane 1993 Malaysia
ALR 2196003-XX-XXX 2196003-00-200 Standard plungers; other details unknown Lasered 1997-11-15 Mexico