BTC 51 series

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    BTC 51 series is a series of conductive BTC dome with slider keyboards from BTC.

    Series

    Confirmed models according to the user’s guide are 5139, 5149 and 5169; 5140 is included for convenience, and the exact scope of this series is not known for certain. Model 5139 is not to be confused with the totally different BTC 5139 series. Three separate FCC IDs have been found associated with keyboards in this style.

    The 5130 and 5131c keyboards by Packard Bell use a different chassis, but the same switches as the mainline 51 series. 71, 72, and 79 series of keyboards are related, use the same switches, and very likely the same PCBs.

    Other brands that used these series of keyboards as a basis of theirs include Wyse, Commodore (owned by Tulip), Laser, and possibly others.

    Note that later BTC 51 series changed to the much cheaper rubber dome over membrane design with no sliders, many of those keyboards have a hollowed-out looking back, and the M in their name possibly indicates that these are membrane models. They also often came in differently styled chassis than the older mainline models.

    Description

    The case features a subtle reverse curve to the case. As such, not all model numbers fit this pattern.

    The keycaps are made of thin ABS and have laser-etched or pad-printed legends. The profile is similar to Signature Plastics DCS family profile, but different to SP’s keys on the inside. Although the key stems are Cherry MX mount, the stabilised keys (2 unit and larger) are not compatible with Cherry MX stabilisers. The series uses a 1.25 unit Esc key, which is a signature feature of BTC keyboards of the early days.

    Variants

    5139

    Focus layout.

    5139 E5XKBM111

    • Packard Bell 5139 -- top.jpg
    • Packard Bell 5139 -- branding.jpg
    • Packard Bell 5139 -- slider.jpg
    • Packard Bell 5139 -- PS-2 plug.jpg
    • 249px Packard Bell 5139 rear label

      Rear label, with E5XKBM111 FCC ID

    5139 E5XKBM10140

    The model number is not written on this keyboard. The PCB is marked “5139”, but then so is the 5149. The layout however is identical the the normal 5139. The similarity in production dates between the PCB and IC suggest high production volume. This keyboard is from 1996.

    • 250px 5139 front
    • 249px 5139 rear label
    • 249px 5139 controller

      Intel-based keyboard controller, dated 9614

    • 250px 5139 PCB
    • 250px 5139 dome sheets
    • 249px 5139 mount

    5140

    “5140” is the most confusing model number, as it relates to different layouts, eras and connectors. The 5140 number was also used for the Packard Bell 5140M (FCC ID E5XKBM104M10U), a more modern style keyboard of unknown construction but with the same reverse curve shape.[1]

    5140 E5XKBM10510

    104-key focus layout, with Windows keys and AT Plug with beige keycaps. PCB marked BTC 5140/7131/7931. The controller is BTC UM6868-03 ( seen on the photos below ), and is dated to the 12th week of 1996.

    Possibly there is also ISO-layout version with this FCC ID using controller BTC-marked UM6868A-0021.[Citation needed]

    • 250px 5140 focus front

      BTC 5140 focus layout front

    • 250px 5140 AT Plug
    • 250px BTC 1540 rear label
    • 250px BTC 1540 PCB
    • 250px BTC 5140 ISO Controller

    5140 E5XKBM10410

    104-key Focus layout with Windows keys and AT plug. FCC ID is E5XKBM10410; date is not known but it will be 1995 or later.

    There’s also an ISO-layout version. The sample unit is made in late 1995 according to the date on both the PCB and MCU.

    • 249px BTC 5140 top
    • 249px BTC 5140 AT plug
    • 249px BTC 5140 rear label
    • 250px BTC 5140 ISO top.jpg
    • 250px BTC 5140 ISO rear
    • 250px BTC 5140 ISO PCB contact side

      ISO model PCB contact side

    • 250px 20210319 153518

      ISO model PCB component side

    • 250px BTC 5140 ISO rubber domes.

    5149

    ISO layout; PCB and controller chip are marked “5139”, which indicates that the 5139/5149/5169 are sharing the same PCB, further proven by most if not all 5139 PCBs have contact pads to accommodate different layouts. This version has been found to suffer from ghosting; normally, potential ghosts are blocked, but playing Tyrian Destruct with two-player keyboard sharing revealed a flaw where a ghost could be emitted, requiring player 2 to use the alternative set of keys.

    • Packard Bell 5149 -- front.jpg
    • 249px Packard Bell 5149 rear
    • 249px Packard Bell 5149 rear label
    • 249px Packard Bell 5149 upper shell with sliders and loose domes

      Loose domes over the sliders

    • 249px Packard Bell 5149 PCB with dome sheets
    • 250px Packard Bell 5149 loose domes

      Loose domes; the single yellow dome is from the space bar

    • 249px Packard Bell 5149 domes
    • 249px Packard Bell 5149 sliders
    • 249px Packard Bell 5149 PCB%2C rear

    Source