5150 Keyboard Malfunctioning

[gkavner]

Recently I pulled my 5150 out of storage and it wouldn't boot. I followed this guide removing the failing tantalums and it all worked fine (I never go round to replacing them though.)

Now when I boot up and begin typing the keyboard throws out occasional incorrect characters, goes upper case sometimes and intermittently just locks up so no entry can be typed. To open apps requires a frustrating retyping many times to get the correct characters up there.

Are the missing tantalums the problem? Does the keyboard rom need reseating/replacing or is the keyboard at fault?

Thanks.

 

[angel_grig]

You have replace the tantalums first,and then search for another problem...

 

[mbbrutman]

You might have a bad DIN connector - a broken wire that is intermittent could cause some of those symptoms. Try applying pressure to the DIN connector when things are not working. If that changes the problem, then see this:

http://www.brutman.com/IBM_PC_Keyboard_Plug_Repair/IBM_PC_Keyboard_Plug_Repair.html

 

[pearce_jj]

All mine do this - it's due to the foam breaking down inside them. To correct the problem, leave them powered on for a bit, then invert and tap the palm end against the desk a little. Next restart the machine and all should be good (until next cold boot).

 

[mbbrutman]

What foam? A 5150 keyboard (original IBM I presume) would be using some form of bucking spring.

 

[modem7]

or is the keyboard at fault?

Presumably, you do not have a spare PC/XT-class keyboard to try.

Are the missing tantalums the problem?

Unlikely. Also, the keyboard uses only the +5 volt line, and I'm very certain (based on known history) that the tantalum capacitors that you removed were on the +12 volt and -12 volt lines (i.e. having no filtering impact on the +5 volt line).

 

[modem7]

The solder joints of the DIN connector on the motherboard are placed under some physical stress each time that the keyboard is plugged and unplugged from the motherboard.
And so a cracked solder joint there is a possibility.

Note: In my experience, a cracked solder joint rarely looks as obvious as the one pictured below. I mechanically enhanced the crack for the photo.

 

[gkavner]

The solder joints of the DIN connector on the motherboard are placed under some physical stress each time that the keyboard is plugged and unplugged from the motherboard.
And so a cracked solder joint there is a possibility.

Note: In my experience, a cracked solder joint rarely looks as obvious as the one pictured below. I mechanically enhanced the crack for the photo.

Yep. That was the problem. Applying downward pressure on the Din plug whilst typing fixed the problem. I sure wish I hadn't left that pc in storage so long. Time to do a teardown and get the soldering iron out!

Thanks everyone for the help.