Amiga 4000T Mouse Troubles

[Castellen]

The quadrature mouse movement data is read by a 74HC166 parallel to serial shift register which is U541 in the A4000T or U975 in the A4000D.  This shift register is read by U450/Lisa.  Replace the 74HC166 and it'll probably be fine.  It's a SO16 package.

If you have left/right buttons, it indicates these lines are being correctly read by the analogue to digital converters in Paula.  You need to double check that you have +5V between the mouse port pin 7 and ground if you're still having problems.

I've wrtten an article on the same thing here if you need more detail.

[Castellen]

When i move the mouse it doesnt move but it acts like im pressing buttons

Mouse buttons do not work when pressed.

OK, so in summary neither movement or button presses are working, but when you attempt movement then you get the same behaviour as when the buttons are pressed.  i.e. objects underneath the pointer get selected or the top menu gets selected.  It's even more unusual that movements could be triggering left/right button presses.

It's unusual that both the movement and button presses are affected as these functions are handled by completely separate function blocks on the main board.

The buttons don't require any 5V on the mouse port to operate, they simply pull the relevant lines to ground/0V.  So it maybe worthwhile checking you have a valid ground on pin 8 pf the mouse port.  You should measure less than 1-2 Ohms from pin 8 to the chassis or general ground on the main board.

Trying another mouse is a good suggestion too.  Also make sure the front panel key switch is in the run position, but this will only affect mouse movement and not button presses.  Check the mouse port ribbon cables are plugged into the main board correctly and not offset by one row or anything silly.

See if the joystick port is working or has the same problem.  Use one of the many applications from Aminet for this, e.g. JoytestMUI.

If you have any test instruments, you can see if there is quadrature data at the input of U541 (pins 2, 3, 4, 5).  A4000T schematic of this here.  My paper copies of this are hard to read, but the circuit is practically identical that of the A4000D.

Likewise, the button inputs are easy enough to test.  Pin 36 on Paula should go from 5V to near 0V for a right mouse button press and pin 10 on U350 should go from 5V to near 0V for a left mouse button press.

[Castellen]

Many thanks for the reference, I wasn't aware someone has recently re-drawn most of the original C= schematics.  They've made a superb job.

[Castellen]

Ok in Amiga Advanced Analyzer
Port 0 (Mouse):
Pin 1: Up (Lights Up But cannot move mouse cursor Up)
Pin 2: Down (Lights Up But cannot move mouse cursor Down)
Pin 3: Left (Does not light up But mouse cursor does move left/right)
Pin 4: Right (Works)
Pin 5: Fire2 (Do not have 3 button joystick)

I'm not familiar with that analyser software, but it appears that there is certainly a problem regarding the movement as you already know, though the left/right mouse buttons are working correctly.

Replace the 74HC166 shift register as discussed earlier in the thread and this is likely to fix your issue.