polyex Posted January 11, 2019 Share Posted January 11, 2019 Was typing along fine. I restarted my Model IV and now they keyboard is acting strange. When I press the 'D' key, I get 'C' on the screen . When I type 'T', I get 'S'. This is all consistent. Could I possibly have done something or do I need to open it up and check connections? Regards, Adam Quote Link to comment Share on other sites More sharing options...
polyex Posted January 11, 2019 Author Share Posted January 11, 2019 After playing with it a bit, it is now behaving as if the shift key is pressed, even though it is not. I get " instead of 2 , # instead of 3 etc... Not sure if there is a common fail point I could check. Any help is appreciated. Quote Link to comment Share on other sites More sharing options...
George Phillips Posted January 11, 2019 Share Posted January 11, 2019 The keyboard is directly addressed and pretty simple (see below). The keys themselves are just switches which connect rows and columns. I can't see any way they'd cause keys to move across columns. A shift key could be stuck on but it would have to be physically jammed down. The usual problem with these keyboards is keys stop working due resistance build up inside the key, broken traces or bad solder joints on the keys. The buffer/inverters that read the columns may be going wrong. A stuck bit from them would explain the shift key problem. I suppose it is possible they could cause the columns to apparently shift. If you do open your machine to poke around be very careful you don't damage the neck on the CRT. MEM. 128 64 32 16 8 4 2 1 ...................................... Model 1/3 Model 4 map 2 14337= G F E D C B A ` $3801 $F401 14338= O N M L K J I H $3802 $F402 14340= W V U T S R Q P $3804 $F404 14344= Z Y X $3808 $F408 14352= 7 6 5 4 3 2 1 0 $3810 $F410 14368= / . - , ; : 9 8 $3820 $F420 14400=SPC RT LT DN UP BRK CLR ENT $3840 $F440 14464= F3 F2 F1 CAP CTL RSH LSH $3880 $F480 Quote Link to comment Share on other sites More sharing options...
polyex Posted January 12, 2019 Author Share Posted January 12, 2019 (edited) I see there are hex inverter in U29 and U30 that buffer the address lines. I will pull the board and try replacing them. I don't think it is a trace problem just because the keys seem to work, they are just spitting out the wrong value on screen. Edited January 12, 2019 by polyex Quote Link to comment Share on other sites More sharing options...
polyex Posted February 6, 2019 Author Share Posted February 6, 2019 Replacing U29 and U30 fixed it. 2 Quote Link to comment Share on other sites More sharing options...
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