Apple IIe stuck in diagnostic mode

[phogren]

on power up goes into diagnostic mode, like no keyboard attached. 1984 motherboard 607-0187-A
Seems to complete mode by beeping at the end but goes back to diagnostic mode.
I have tried different keyboards but no change.
I can do control-open apple-reset and get the command prompt and can run a simple program that seems to run OK

 

[HoJoPo]

Sounds like it's detecting the open and closed apple keys being depressed, which is a way to start diagnostics at power on. These are also the joystick buttons, maybe something is triggering them?

There is an LS251 multiplexer chip (UC12) that reads these buttons / apple keys. Here's the schematic, it's on part 2: https://archive.org/details/Schematic_Diagram_of_the_Apple_IIe/page/n1/mode/2up

This simple BASIC program will read and report the joystick / open and closed apple status, > 127 reading will show the button is pushed:

10 LET X = PEEK(49249)
20 LET Y = PEEK(49250)
30 PRINT "BTN0=";X;" BTN1=";Y
40 GOTO 10

 

[phogren]

Interesting, The program shows 160 and other numbers. I am assuming I need to replace that chip.

 

[HoJoPo]

It's possible that the keyswitches have failed. Check the keyboard and make sure the open/closed apple keys aren't shorted when not pressed.

 

[KDawg]

also check the cable to make sure connections are not broken, as you mentioned in your first post the Apple ][ series fails to diag mode if no KB is attached