Trivia, Model M & F

Model M ; Buckling Spring Technology and membrane switching system

Cut model of a Buckling spring key

Springs and hammers

Inside Model M

Repairing Model M ( reuse inner assembly )

Model F ; Buckling Spring Technology and Capacitive switching system

A sample of capacitive switch keyboard . p/n 5640991

Variations of Control PCB

Pin out of SDL connector and PS/2 plug ( and AT DIN plug )

Pin out of J7 Terminal keyboard ( 5 pin header )

Stabilizing Rod ( added 2009/08/03 )

Translucent Key Caps ( From Korean web site, United Keyboard Mania by zoOoz )

English translation, Japanese translation

Model M can't be recognized when connected to some modern mother board.

How to reduce Buckling sound

U.S. Patents relating buckling spring technology

Catastrophically buckling compression column switch and actuator; No.3,699,296, Oct.17,1972

Pushbutton switch assembly with pivotable conductive ... ; No.3,731,030, May.1,1973

F Buckling spring torsional snap actuator; No.4,188,611, Oct. 3, 1978

M Buckling switch actuator for low force membrane contact switch ; No.4,584,317, Jul, 9.1985.

IBM document introducing model M

Development of a membrane switch-type full-travel tactile keyboard

Buckling Spring Technology and membrane contacts.

Please check Buckling Spring section of Qwerters Clinic maintained by Mr. K. Tanaka//. You can see

everything about Buckling spring mechanism there. This page explains IBM Japan 5576-A01 keyboard but the buckling mechanism is basically same with 101 key enhanced Model M. except the fact that A101 uses individual key modules.



For Japanese readers. KEN-JIN web site maintained by IT-san is also recommended to understand buckling spring technology and its brief history.

Buckling spring key; Cut model

Great thanks to Mr. K. Tanaka// ( The owner of famous web site " Qwerters Clinic ") who offered wonderful pictures.

I nner structure of a key top is designed to let the spring bend toward designated direction only inside a key unit. When a spring completely bends ( buckles ) , it will hit actuator and generates clicking sound and at the same time a platter ( or hammer ) at the end of the spring will hit and press membrane sheets ( membrane sheets are covered by a black rubber sheet . You can't see membrane sheets in above pictures. )

Springs and hammers

Coil springs and hammers used in model M2 ( including 42H0468 ) are identical with those used in Model M.

Some models have black hammers while the others have white half-translucent hammers.

Those coils and hammers can be interchangeable among all of model M ( of course except rubber spring type M ).

Japanese readers are advised that coil springs in 5576-A01/003 are different from those used in Model M. They are shorter than Model M springs.

Pictures below show deference of an actuating rocker (hammer) of Model M and Japanese A01

L; Model M R; Japanese A01 L; Model M, R; Japanese A01 L; Model M, R; Japanese A01 Bottom view Upper view Upstanding post on the upper surface of a rocker

Is there any rule to set a spring to a hammer ?

As far as I can see, every springs set on each hammers with a starting point of coil spring locates within 180 to 270 degrees. Don't know if there is any reason for it. If I set a spring in different position, buckling error occurs frequently.



How to reduce Buckling sound

If you feel your M is too loud when you type and you want to reduce buckling sound without changing your M to a cheapo membrane keyboard .

Use silicon grease. Pull out key assembly and paste a little dose of silicon grease around the wall of barrel and buckling springs. You can control sound level with the volume of grease.

Spray type silicone grease is also easy to use.

............And actually IBM provided such a variant of Model M.

Model F ; Buckling spring technology with capacitive switches

Model F was introduced together with the IBM PC. Key action is US patented IBM Buckling technology and the switching system is so called capacitive contacts switch. Capacitive switch does not require any physical contacts between two terminals. Specially designed electrical components detects changing of capacitance between terminals and at some point of capacitance, switch turns on. Model F uses plastic made platters ( hammer lever ? ) to change capacitance of each switches, When a platter hits main PCB, capacitance between two terminals on the PCB placed below a platter increases and immediately a switch turns ON. Capacitive switches made by other manufacturers such as Keytronic, BTC and TOPRE ( a Japanese manufacturer which still makes very expensive keyboards with capacitive switches ) do not generate clicky sounds. Only IBM's model F with buckling system makes louder clicking sounds when platters hit main PCB directly. Those who like IBM model M may like IBM model F but those who does not like model M because of its buckling sounds definitely dislike model F . Because Model F is much louder than Model M when we type. I like model F so much. Model F AT 84 key keyboard is the one you can use with usual PCs without any modification. You just need an AT to PS/2 cable to use the keyboard.

English explanation about Capacitive switch is available in this web page.

The author misunderstand about mechanical switch because the author introduced buckling mechanism of model F as an example of mechanical switch. As far as Capacitive switch concerns, the explanation seems to be correct..

Please examine U.S. Patent No.4,188,611 for further detailed information.

Let's see inner layout/parts of p/n 5640991

5640991

ID 380X N-1797

Date 47-1983,

Mod C-1, ( I think "Mod." doesn't mean "Model". "Modification" may be?

Made in U.S.A. by IBM , Armonk. NY. USA

Description : One piece made key top, Buckling Spring Technology, 15 pin D-sub connector. Data processing keyboard ?

Glass fiber PCB is attached on the curved lower steel plate. PCB itself is not flat but is also in a wide curve.

Looking from the bottom side of the lower steel plate





Left side; Comparator?

A large DIP module might be a controller. It 's marked as "8310354 8332, PI P A 998741, L3374976, Intel "

Back View of a controller PCB





Some kind of coating covers surface of the main PCB including every terminals of signal line ( large square parts ) .

Look carefully a close look of terminals. You can identify no cupper surface is exposed on the main PCB.

Wow! Such a big plater ( blade, hammer lever , I don't know how IBM named it. )

The lever is made of carbonized plastic.

When the key press downward and the hammer meets terminals on the PCB, capacitance between the terminals are increased and then a switch turns ON. i don't know detailed mechanism.

Every actuators can be removed from metal base plate ( upper plate ).

Do not pull out a space bar from this keyboard, XT 83 key keyboard and AT 84 key keyboard. Stabilizing bar is set underneath the upper metal plate and you can't place it properly unless you disassemble the keyboard .

That's why I can provide above pictures. I knew that, but I just forgot about it when I pulled out keys to make them clean......

Front view of P/N 5640991 Keys except text/data keys may be placed wrong position.

Forgot to take pictures before I pulled out all the keys :-)





Variations of Control PCB

Also check Model M keyboard section of Ardent Tool web site maintained by Louis Orland.

K/B P/N CTRL PCB U2 P/N RMRKS 1390120 1389989 1389986 1391401 1389989 1389986 1391401 1392993 1389986 1391401 1393291 1393295 1388032 1351523 1386032 Incompatible with Wintel PC 59G7980 1398011 1394080 1390680 1387210 1387213 Incompatible with Wintel PC 1319472 1390536 1390538 Space Saver M 42H1292 11A0162 1428578 Totally different from other PCB.

1389989 K23-3*1 EC528561 1087, dimension 170mm x 50mm

Pulled from Model M P/N 1391401, 13MAR87 made .

# 1087 following to EC number probably indicates mfg week/year ( 10th week of 1987 ).

U1/U3 : 2392161 U2 : 1389986

There is a 4 pin header J2 at the right side of the PCB to which 4 yellow wires from LED block are connected ( not a film printed cable ).

P/N 1390120 sold with the last PC/AT has the same control PCB.



*1 The number begins in K-prefix varies among models. For example,

the number of a control PCB of model 1390120 in my hand is " K26-1".





Signal assignment of connector J1

1392993 K26-1*1 EC 528682 3787, dimension 170mm x 50mm

Pulled from Model M 1391401 manufactured in 22SEP1987.

Almost same with 1389989 above. There are 2 capacitor packs at the position of CP1 and CP2 below J4. Except these two register packs, This PCB seems almost same with 1389989. ( I'm not so sure whether "CP" means capacitor packs or not. )

U1/U3 : 2392161 U2 : 1389986, CP1 & CP2 : B9HC0114 102M x8



Two brown capacitor packs are soldered below J4 .

1351523 K26-3*1 EC528682 39/87, dimension 170mm x 50mm

U1/U3 2392161, U2 1386802, CP1/CP2 ; Solder pads

Looks like almost same with 1389989 1392993 except missing 2 brown capacitor packs below J4. There are solder pads at the position CP1 and CP2 . Main control chip is different from above 2 PCBs.



This PCB is used in Gray color model M keyboard with a black square logo plate , Part number 1388032 , ID 1001377, Date 02OCT87, Plt J3

The keyboard doesn't work with a usual PC ( I mean Wintel PC not a genuine PS/2, don't know if if works with a PS/2 ) . I don't know if those missing CP1/CP2 blocks have some effects on this issue. Or if the difference of controller chip P/N causes the problem... When I swap the control PCB to a 1392993, the keyboard works properly.



2004.06.27

Examined DC level of data/clock line and found each lines are something around 2.1V while others keyboards are around 4.8V. Then I tried data/clock line modification adding 2x 4.7K ohm registers according to IBM PS/2 Keyboard modification page .

Result ; No luck.. Three LEDs flashed repeatedly and PS/55E gave 301 error again.

Conclusion : Model M P/N 1388032 with a controller PCB P/N 1351523 might be a proprietary keyboard for some special system. Most possibly Keyboard controller is not compatible with usual PCs. ( Or mine has a defective controller PCB )

1393291 KF530-3, EC 528693 4488

Made in 44th week 1988? ( Mfg date of the keyboard is 25OCT88 )

U1/U3 : 2392161 U2 : 1393295

Connector at J2 is missing, instead there is J8 for film cable connector for LED block

Seems to be a popular type of control PCB used in earlier type of Model M between 1988 and 1990 .

Main difference is connection between a control PCB and LED block. Each PCBs are connected via film cable instead of wires with 4 pin headers.

Variations of this PCB in smaller dimension can be seen in Louis's page.

1398011

PCB is pulled from a Model M P/N 59G7980 by Lexmark with drain holes, blue logo on a gray round plate, manufactured 02FEB1993.

Film cable for LED block is combined with matrix lines and connected to J3 on the PCB together with key matrix lines. This PCB is made in HongKong.



1387210 K26-3, EX528635 0987, possibly made in HongKong

Pulled from 101key terminal keyboard ( not sure ) Model M P/N 1390680, MFG date 02MAR87.

J7: 6pin connector ( Uses 4 pins only , 5 pins are ready ) for keyboard cable.

J6: Unknown , shortened to PCB GND with a metal alloy.

U2: IBM 1387213 ( HD6805V1NO1P )



At the end of the cable, it has a strange AT like sideway plug. You can see a picture of the same plug and the pin out can be seen in this page .







Pin out of connector J7, 5 pin header ( on the controller PCB )

Bottom left : Clock , to the Yellow cable

Bottom center : GND , to the White cable

Bottom right : DATA, to the Red cable

Upper right : +5V , to the Black cable



Keyboard p/n 1390680 has very funny characters at the position of Numeric Keys. Numeric keys are available at the upper row of text/data keys ( below Function keys ) .

This Control PCB does not work on with Windows PC.



1394523 EC. 528735

Pulled from 122 key terminal keyboard P/N 1394099 , MFG date 05-05-97, manufactured in UK by IBM ( not Lexmark ).



Cable connector is marked as J1 ．

J5/12 pin header connector is left open. ( no cables are connected ).

U2 P/n is 1394068 ( EF6805U3P-BE512 ).



Not sure about a plug at the cable end ( the cable was cut at the keyboard side . I got the keyboard for "parts" ) . I assume the plug might be either RJ11 or RJ45.



1390536 EC528682, K23-3, 5287

U2 : 1390538,

CP1/CP2 : Solder pads are there.

J2 connector for LED block is missing

U2 : Absent ( outline only )

Pulled from Space Saver Model M P/N 1319472, Date 15JUN87.





Stabilizing Rod

In addition to Space Bar, early models of 1391401 have stabilizing rod beneath both "Enter" and "+" key at numpad section. This design was already seen in 1390121 and 1390130 sold together with late XT and AT computers respectively, one year earlier than appearance of 1391401 and PS/2 computers .



1390121

1390131 Sorry can't find clean one

1391401 '87 made

13912401 '88 made

1392598 ( Not 1391401 but 87 made Model M )

1391401 '88 made in UK ( US layout )

Seems like IBM changed design at some point in 1989

Some of 1391401 made after 1989

Model M can't be recognized when connected to some modern mother board