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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: TheMagicM on March 27, 2017, 03:34:07 AM

Title: Amiga 500 mouse irratic
Post by: TheMagicM on March 27, 2017, 03:34:07 AM

I have this spare a500 and the mouse acts very erratic.  It'll jump around here and there.  What chips could be the culprit?   I've replaced even/odd CIA chips and the Paula chip.    


I also had issues to where DF0 and DF1 couldnt format a disk.   I think the CIA chip replacement took care of it.   I'll have to write some ADF's to disk to double check that part.

Title: Re: Amiga 500 mouse irratic
Post by: CodePoet on March 27, 2017, 08:02:31 AM

Here's the A500 PDF Schematic (page 6 is what you're after): http://www.amigawiki.de/dnl/schematics/A500_R6.pdf

It could be one of the following components:

• Bad/Damaged U15 (74LS157 Quad 2to1 MUX)
• Dry solder joint on one of the RP401 pins (4.7K pull-up resistor pack)
• Bad/Damaged Denise chip (more likely a bad connection)

I don't think it'd be one of the EMI components, most likely you have a dry solder joint between CN1 and Denise, or U15 has become faulty

Edit: I guess it could also be a fault with U33 (74F04 Hex Inverter) or E109 (47pF cap) - This line controls the select input of U15 - The failure of U33 would cause errors sampling left and right joy ports and make the mouse move intermittently

Title: Re: Amiga 500 mouse irratic
Post by: TheMagicM on March 27, 2017, 01:59:23 PM

I'll double check it.   Thanks!

Title: Re: Amiga 500 mouse irratic
Post by: LoadWB on March 27, 2017, 02:22:28 PM

FWIW, most likely not the case in your situation, but for anyone who has ever had this problem and has used the Cocolino PS/2 mouse adapter in the past, make sure the cocolino.driver is not in your SS or US.  I haven't used my Cocolino for a few years, since I got the Deneb, and recently while I was installing a new drive I found the Amiga mouse was going nuts like yours.  Removed the cocolino.driver and all is well.