Jump to content
IGNORED

130 XE keyboard membrains


Welsh Wizard
 Share

Recommended Posts

  • 3 weeks later...

Both of my 130 XE's have failed on the keyboard membrain the tracks have cracked , I tried using the the conductive pens but it only last for about a hour or so before they crack some where else or in the same place, so I am looking for a supplier or some one who has some spare membrain matrix sheets.

I know you are probably looking for somewhere closer to home, but the only supplier I know of other than getting one from another XE computer is Best Electronics. They list 2 different replacement mylar membranes on this web-page:

http://www.best-elec...a.com/130xe.htm

Link to comment
Share on other sites

  • 3 months later...

The type of keyboard used is known as a "Low-resistance contact", the

resistance being about 1000 ohms or so. As you use the keyboard, the

resistance of the contacts tend to go up. For the regular keyboard and

the RESET key, this increase in resistance causes no problems. But the

console keys (OPTION, SELECT, and START) are read by a different IC, and

the change in resistance will eventually keep the console keys from

working. (The HELP key is actually read as just another letter key).

 

The fix to the problem is to add just enough resistance in parallel to

the key so that it is high enough not to make the computer read the key

as pressed, but low enough that when the console key is pressed, the

computer will recognize it.

 

The original idea for this fix came from Alan Haskell from the book "Mods,

Fixes, and Upgrades" available from Best Electronics, 2021 The lameda,

Suite 290, San Jose, Ca.5126.

 

One minor problem with the fix, however - it wouldn't work on the 130XE

that was given to me to repair. After several hours of pulling out my

hair over this thing, (and anyone who has seen my balding head KNOWS I

can't afford to do too much of that!) I determined the problem.

 

The resistor value given - 3000 ohms - was too low, for this machine at

least. This value was just slightly above what the computer registered

as a key pressed. Any random electrical noise would cause the computer

to read the key as pressed, which would cause problems with the BBS

program that was being used. A higher resistor value was needed.

 

Theres no "correct" resistor value to use, as it varies between different

130XEs. You may need to do some testing (as I did) to make sure it works

properly.

 

What You Need:

 

Soldering Iron and Solder

Wire Clippers

(3) 4700 Ohm Resistors, 1/4 watt

A small Phillips screwdriver

Needle-Nosed Pliers

 

How to do it:

 

1) Unplug all of the wires from the computer.

 

2) Turn the computer over and remove the four screws that hold the top

cover on.

 

3) Turn the computer back over and THEN take off the top cover.

 

4) Lift the keyboard up and forward and you should see the ribbon

connector at the lower right corner. Gently remove the ribbon from

the connector.

 

5) Remove the screws that hold the motherboard to the lower half of the

case. Lift the front part of the motherboard up and then forward to

remove it from the case.

 

6) Straighten the tabs that hold the top and bottom shields on and remove

the shields.

 

7) Turn the board over with the keyboard connector facing to the front.

The connector pins are numbered from right to left. Pin #3 is the

ground connection, and Pins #21, 22, +23 are the pins for START,

SELECT, and OPTION keys, respectively. These are the connections you

need to make for the repair.

 

8) Take the three resistors and solder the wire from one end of one

resistor and solder it to the second resistor, at the spot where the

wire comes out from the connector, being sure to cover them with a

short piece of insulation as well.

 

9) Check your wiring to be sure that there are no shorts!

 

10)Use as little solder as possible, and make the connection as fast as

you can, using as little heat as possible. Place a short piece of

electrical tape under on the board under the resistors, if needed,

and press the resistors close to the board.

 

11)Reassemble the shields and check to see that the resistors are not

shorting against the lower shield.

 

12)Reattach the keyboard to the motherboard, taking care not to bend the

ribbon - it WILL crack. It helps to insert one edge first, then

carefully work the other edge into the connector.

 

13)To test the repair, power up the computer and in BASIC type:

 

10 PRINT PEEK(53279):GOTO 10

 

and type RUN. You should see a vertical row of 7's. Pressing OPTION will

give you 3's. SELECT will give you 5's and START will give you 6's. The

value should not change while any one key is held down. This should

return the normal function of the console keys.

 

Special Note for Techs:

 

You can use the following method to determine the exact resistor value

that you need. It might save you time and aggrivation:

 

What you need (in addition):

 

Multitester (digital best)

10K Multiturn Potentiometer

Some short pieces of thin wire

 

This should be done between steps #4 and #5 of the above procedure:

 

A) Connect one short piece of wire to the center pin of the pot, the

other to one of the other pins.

 

B) Solder the free end of one wire to the ground pin (Pin 3). These

connections will only be temporary. Solder the other free end to one

of the console key Pins (21,22, or 23).

 

C) Adjust the pot for maximum resistance.

 

D) Reconnect the power and monitor. Reconnect the keyboard. Turn on

the computer with the option key pressed - you should get the

diagnostic screen. Select the KEYBOARD TEST and hit START.

 

E) Adjust the pot until the tone just starts to sound intermittently.

Measure the resistance by connecting the probes to the center pin and

the unused pin on the pot. Subtract the measured value from the rated

value of the pot to get the proper value. Record it.

 

F) Adjust it again until the tone sounds continuously. Record the value

the same way as in step E.

 

G) Turn the computer off, and disconnect the cables and the keyboard.

Unsolder the wires from the keyboard connector.

 

H) The proper resistor value to use will be the closest value that is

both HIGHER than the highest value recorded, but around DOUBLE the

lower value. The resistors you will use will probably be between 3000

and 5000 ohms. Continue on to step #5 as above.

 

I dug this up out of an old BBS..... and it has solved all but one out 20+ supposedly broken trace mylars I have been confronted with... if you do cause a crack it is normally on the short strip from the keyboard to the main board I just paint it and put it in when the traced parts are still damp... if you make the the trace to thick or put it in while completely dried when it bends it will crack again ... less is more!

  • Like 3
Link to comment
Share on other sites

  • 8 months later...
  • 4 years later...

The type of keyboard used is known as a "Low-resistance contact", the

resistance being about 1000 ohms or so. As you use the keyboard, the

resistance of the contacts tend to go up. For the regular keyboard and

the RESET key, this increase in resistance causes no problems. But the

console keys (OPTION, SELECT, and START) are read by a different IC, and

the change in resistance will eventually keep the console keys from

working. (The HELP key is actually read as just another letter key).

 

The fix to the problem is to add just enough resistance in parallel to

the key so that it is high enough not to make the computer read the key

as pressed, but low enough that when the console key is pressed, the

computer will recognize it.

 

The original idea for this fix came from Alan Haskell from the book "Mods,

Fixes, and Upgrades" available from Best Electronics, 2021 The lameda,

Suite 290, San Jose, Ca.5126.

 

One minor problem with the fix, however - it wouldn't work on the 130XE

that was given to me to repair. After several hours of pulling out my

hair over this thing, (and anyone who has seen my balding head KNOWS I

can't afford to do too much of that!) I determined the problem.

 

The resistor value given - 3000 ohms - was too low, for this machine at

least. This value was just slightly above what the computer registered

as a key pressed. Any random electrical noise would cause the computer

to read the key as pressed, which would cause problems with the BBS

program that was being used. A higher resistor value was needed.

 

Theres no "correct" resistor value to use, as it varies between different

130XEs. You may need to do some testing (as I did) to make sure it works

properly.

 

What You Need:

 

Soldering Iron and Solder

Wire Clippers

(3) 4700 Ohm Resistors, 1/4 watt

A small Phillips screwdriver

Needle-Nosed Pliers

 

How to do it:

 

1) Unplug all of the wires from the computer.

 

2) Turn the computer over and remove the four screws that hold the top

cover on.

 

3) Turn the computer back over and THEN take off the top cover.

 

4) Lift the keyboard up and forward and you should see the ribbon

connector at the lower right corner. Gently remove the ribbon from

the connector.

 

5) Remove the screws that hold the motherboard to the lower half of the

case. Lift the front part of the motherboard up and then forward to

remove it from the case.

 

6) Straighten the tabs that hold the top and bottom shields on and remove

the shields.

 

7) Turn the board over with the keyboard connector facing to the front.

The connector pins are numbered from right to left. Pin #3 is the

ground connection, and Pins #21, 22, +23 are the pins for START,

SELECT, and OPTION keys, respectively. These are the connections you

need to make for the repair.

 

icon_cool.gif Take the three resistors and solder the wire from one end of one

resistor and solder it to the second resistor, at the spot where the

wire comes out from the connector, being sure to cover them with a

short piece of insulation as well.

 

9) Check your wiring to be sure that there are no shorts!

 

10)Use as little solder as possible, and make the connection as fast as

you can, using as little heat as possible. Place a short piece of

electrical tape under on the board under the resistors, if needed,

and press the resistors close to the board.

 

11)Reassemble the shields and check to see that the resistors are not

shorting against the lower shield.

 

12)Reattach the keyboard to the motherboard, taking care not to bend the

ribbon - it WILL crack. It helps to insert one edge first, then

carefully work the other edge into the connector.

 

13)To test the repair, power up the computer and in BASIC type:

 

10 PRINT PEEK(53279):GOTO 10

 

and type RUN. You should see a vertical row of 7's. Pressing OPTION will

give you 3's. SELECT will give you 5's and START will give you 6's. The

value should not change while any one key is held down. This should

return the normal function of the console keys.

 

Special Note for Techs:

 

You can use the following method to determine the exact resistor value

that you need. It might save you time and aggrivation:

 

What you need (in addition):

 

Multitester (digital best)

10K Multiturn Potentiometer

Some short pieces of thin wire

 

This should be done between steps #4 and #5 of the above procedure:

 

A) Connect one short piece of wire to the center pin of the pot, the

other to one of the other pins.

 

B) Solder the free end of one wire to the ground pin (Pin 3). These

connections will only be temporary. Solder the other free end to one

of the console key Pins (21,22, or 23).

 

C) Adjust the pot for maximum resistance.

 

D) Reconnect the power and monitor. Reconnect the keyboard. Turn on

the computer with the option key pressed - you should get the

diagnostic screen. Select the KEYBOARD TEST and hit START.

 

E) Adjust the pot until the tone just starts to sound intermittently.

Measure the resistance by connecting the probes to the center pin and

the unused pin on the pot. Subtract the measured value from the rated

value of the pot to get the proper value. Record it.

 

F) Adjust it again until the tone sounds continuously. Record the value

the same way as in step E.

 

G) Turn the computer off, and disconnect the cables and the keyboard.

Unsolder the wires from the keyboard connector.

 

H) The proper resistor value to use will be the closest value that is

both HIGHER than the highest value recorded, but around DOUBLE the

lower value. The resistors you will use will probably be between 3000

and 5000 ohms. Continue on to step #5 as above.

 

I dug this up out of an old BBS..... and it has solved all but one out 20+ supposedly broken trace mylars I have been confronted with... if you do cause a crack it is normally on the short strip from the keyboard to the main board I just paint it and put it in when the traced parts are still damp... if you make the the trace to thick or put it in while completely dried when it bends it will crack again ... less is more!

Great info, thanks! Any chance of a picture of a completed fix so that it's obvious to not-so-techy people like me please?

Link to comment
Share on other sites

  • 2 years later...
On 1/26/2017 at 7:34 AM, ultrasteve said:

Great info, thanks! Any chance of a picture of a completed fix so that it's obvious to not-so-techy people like me please?

Pictures of 2 completed implementations are now over in this topic:

 

  • Like 2
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...