Almost got it, but now a sticky mouse on A500?

[hoptoit]

Anybody having some input on this would be greatly appreciated.  I've  nearly completed updating and restoring our A500 to full operation.  I  did a Chip RAM upgrade by adding x4 DIP sockets and chips, modified JP2  and JP7A, replaced the floppy drive.

But I'm noticing an occasional glitch with the mouse sometimes.  Every  so often it will hang in place on the screen when I'm trying to move the  cursor, usually when moving down or to the right.  It seems to be  momentary, then corrects itself.  But it is very noticeable playing  Marble Madness, as the marble goes off in the wrong direction suddenly.

I tested the phenomenon happening on both ports, and with 2 different  mice - one optical and one ball driven.  It's hard to tell if this is  occurring with the joystick very much.

Capacitors wearing out?  Did the memory modification interfere with  something?  I ran a few memtests and the new memory showed no errors.   This isn't the worst, but any ideas?

[hoptoit]

Is the ball mouse an original Amiga one or is it going through an adaptor? Some adaptors can cause this type of phenomenon and can be picky about the mice that work reliably with them. Also, a basic thing but something that still catches a lot of people out is the surface - some optical mice have trouble on shiny surfaces, even shiny mouse mats. And some ball mice can also have trouble on shiny surfaces, especially if the ball's light and the rollers dirty.

One of them is a PC PS/2 optical going through the Microsys adapter.  The other is a real Amiga ball mouse with logo on it.  I tried a few different surfaces to make sure that wasn't the only culprit.  The mouse buttons seem to work just fine.  I don't notice the problem very much except during a mouse driven game with lots happening on screen.

Follow these steps (if one fails, continue to the next):

1. Check power. A faulty 5v line can get your A500 crazy.
2. Reseat de CIA (the one that is close to the joystick and mouse ports).
3. Swap the CIAs
4. Reseat DENISE chip (It, or she, drives the mouse signals).
5. Replace EMI400 and EMI401 (check value on schematics, It changes from version to version).
6. Replace the 74LS157 chip (U15?)

If your mouse buttons work well, you can skip steps 2 an 3.
I bet It's the 74LS157

Good luck!!!    

Power should be good as I updated to a more modern AC adaptor with +12v/-12v/+5v/GND.  Tested the rails with a multimeter before using it and they were good.

I will give the DENISE a reseat next since I have a PLCC tool around here somewhere.

[hoptoit]

AFAIK DENISE has DIL packaging on A500, not PLCC...
Only AGNUS has PLCC packaging, and It (or she) has nothing to do with the mouse or joystick.

Of course I meant DIL.  And regardless of giving DENISE a quick wipe down and reseat, no change in the mouse behavior.

[hoptoit]

Next logical step is to replace EMI400 and EMI401, but I'm pretty sure the problem is U15 (74LS157).

Just to make sure, would EMI400 and EMI401 be located at U40 and U41 on the A500 Rev6A? Or am looking at the wrong thing entirely?