Amiga 2000 Faulty when mouse pulled in

[LordFire]

Hi,
This might sound strange. I have an Amiga 2000 which boots ok from FDD and HDD and keyboard works ok, but when I plug in the mouse the displayed image goes mono and shifts to the left and the mouse doesn't work. I've swapped out the both 8520 from a working Amiga 500. I've checked for dry solder joints etc. All with no joy.
Any pointers?
Thanks.

[LordFire]

I've tried 2 x original mice and an Amiga 600 vintage mouse. I found the pin outs for the mouse port and I've got a DB9 I'm going to plug in tonight and try some stuff. I suspect it's some thing to do with +5V.

[LordFire]

No the last time I fired it up a week ago it was working. I wasn't aware of PC mice causing damage. But I had just used th Amiga mouse. I hooked up a multimeter to the +5V and only got 2.3. Not sure if i will see 5 when there is no load. Tomorrow night I'll hook it up to the Amiga 500 and see what I should get.

[LordFire]

Ok, looks like the mouse port is powered from pin 12 on the power supply which is '+5V User'. With nothing connected it sits at 2.3V instead of 5V and once I plug the mouse in it drops to 1.65V. When I hook up another +5V cable to pin 12 everything seems to work ok. I opened up the power supply to find I think a non Amiga PS. The Tick wire pin14 wasn't even hooked up. It almost looks like a AT power supply fitted in to the original PS case. I desoldered wire 12 and hooked it up to the main +5V feed. All back together again and it is working all ok now.