Repairing Model M

Re-use a key base assembly 

P/N
42H1492 
( Later model
)

Got a junk Model M P/N 42H1492 made in 1996.  
Condition; Very poor, full of dust and mud hardened with rain. 
One of my net friend found it at a junk yard but he didn't pick it up because it was so dirty and had been there for several rainy days.   I asked him to pick it up and sent it to me for parts.  I thought it might be a good source for a space bar, shift keys, and so on.
Examined the junk 42H1492 and I noticed that a control PCB could not be used for my earlier type of Model M such as 1391401.  Well, all the keys were there, it was just dirty, with plenty of mud, rusty inner steel plate... but it could be refurbished.

  Mud caked key tops.  



Rust began to eat the inner steel plate.  

Round, black parts are melted studs which stand from upper actuator panel . Melted studs keeps actuator panel pressing firmly to the bottom steel plate.  You may see some ( three or four or more... ) of melted heads when you disassemble outer cabinets of model M.  These melted rivets are one of weakest part of model M.   If  a model M looses so many melted heads then it also looses firm tactile feedbacks when we type because both plates may not keep tight connection. 

 

All the melted plastic studs were cut off  so that the steel plate can be removed from the upper actuator panel.
Above picture is the one from model 1391401 which the melted studs were all pulled out.

It is recommended to use bolts and nuts for the holes within red square line.  Especially the middle of three rows requires much force to connect the actuator panel to the steel base plate.  For the other  holes you may use tapping screws without nuts.

For front 2 rows, you need to use conic head bolts in order to avoid heads of bolts meddling with a base cabinet.

 


     Recommendation about bolts

     I used;
     #1. 2mm x 8mm  bolts  plus nuts
     #2. 2mm x 8mm bolts with a conic head
           If you can prepare 2.6mm x 8mm tapping screws
           with a conic head,  it's much better.  
     #3. 2.6mm x 6mm  tapping screws.

 


 

 

Before drilling a hole .
Need to cut every studs from the base. 

 After drilling a hole

 

Set some  screws so that you can place a rubber sheet and membrane sheets at the right position using the screws as studs to guide sheets.


Set every buckling units


Cover the plate with a rubber sheet.

 

Then Place membrane sheets one by one.

 Red circles in the picture are screws as "studs" . Without these studs it may be difficult to set membrane sheets properly.

 

Tapping screws from the steel plate

A screw comes out like the picture.
If you use a 6mm length tapping screw,  a tip of a screw will not come out from the surface of actuator panel.
The pictured screw is in 8mm length.

A screw from the front of actuator panel.

Opposite end of above picture.

A conic head screw from the steel plate  ( A nut is used at the opposit end; front of actuator panel ).

Half done.

Forgot to mention that I grinded the rusty surface of the steel plate with a  sandpaper and polished it beforehand.

 

Finished !


I did not use bolts for the most front row. Plastic studs are still there.  I can't get conic head tapping screws and I did not think  this row should be connected firmly with screws.
Followers are recommended  to use conic head tapping screws for the front row too.

 

 No magic.  Just washed every key tops and front/base cabinets .

 

 

I bet you  will like the touch and feel of buckling action of every keys after you successfully finished repairing  your Model M using bolts and nuts.  It will give  firm response and you may not hear loose resonance of coil springs anymore.

Try  bolts and nuts,
If your Model M lost many melted head of plastic studs and if you  want a superior Model M. 
That's the way you may like

2004.07.19  By Sandy

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