BTC 51 series
|This article requires additional photographic illustration — need photos of 5140 ISO and 5169|
|Layouts||Focus layout, ISO, ANSI|
|Keyswitches||BTC dome with slider (PCB)|
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.
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.
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.
"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.
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]
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.
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.
ISO layout, really hard but thin Abs keycaps. The backspace, and the large keys on the numpad uses guide shaft type stabilizers. The enter and the space uses wire stabilizers.
This is a rare version of which little is known. It has been found with Wyse branding and colours in ANSI layout, with Wyse part number 770180-01 (where -01 is reported to indicate US layout). The FCC ID of this version is E5XKBM111.