• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

Mouse and Keyboard issue on Macintosh SE

tony359

Member
Hi all
This is my first post here, I found this forum while googling for an issue I am having with an SE I am repairing.

Basically, the whole ADB stopped working in between reboots - no, I did not hot-plug my mouse! The mouse was working fine before.

The system boots up, reaches the desktop but when I move the mouse, all that happens is that the "apple" menu in the top left corner opens up. Then nothing. But I did not push the button.

The keyboard doesn't seems to do anything. I can open the debug window and all it types are "AA" for each press of the button (AA for pressing and AA for depressing) up to 2/3 of the first line, then it stops. (see pic below)

Things I checked.
- 5V is present on ADB
- GND is present on ADB
- Interference filter is ok
- I checked for continuity between ADB ports, ADB chip and VIA.
- I checked R14, R15 and the transistor driving the bus from the ADB chip side.
- ADB chip is getting a clock from the GLU chip (3.6Mhz)

Then I fired up my scope.
- ADB signal is present on the bus. Additional signals appear when the mouse is moved.
- I decoded the signal sent by the ADB chip: when just booted up, it's asking address 2 (should be keyboard by default) to "TALK". As soon as I move the mouse, the address changes to "3" which should be the mouse. That seems healthy to me. (see pic below)
- I followed the signal out of the ADB into the VIA. I see signals happening between the two chips when I move the mouse.
- I see extra IRQ signals and "Chip Select" on the VIA when I move the mouse.

The mac repair started with some memory issue so I thought that maybe the RAM addresses where the VIA stores its bits could be damaged. I downgraded the RAM from 4 to 2MB, swapping SIMMs but the issue did not change.

I swapped the mouse with another one and the same happens.

So:
- The issue seems to be on the logic board
- The ADB chip seems to be doing something.
- Signal seems to reach the VIA and get deeper in the Macintosh's guts

At this point I am a bit stuck. I am thinking that maybe the ADB is sending rubbish signals to the VIA (or maybe the VIA is) and the software/hardware receiving the signal is struggling to interpret them? I have some other SE, I could socket the ADB and VIA and test but I also like to understand things so I was wondering if any of you had any ideas of what could be going on here! :)

I've added some relevant schematics 'cause I know they're not so easy to find!

Thank you so much for your help and Happy New Year!

adb2.JPG

adb1.JPG

adbschem2.JPG


adbschem1.JPG
 

Attachments

  • adbschem1.JPG
    adbschem1.JPG
    119.9 KB · Views: 4
Last edited:

tony359

Member
That would be great as I can source a VIA from China but not an ADB chip. Thanks for your feedback.

Can I please check with you where you saw VIA chips to purchase? I see some on ebay, pulled from systems.

Looking here: https://github.com/kr239/Macintosh-SE-Reloaded/blob/master/README.md

it says the Rockwell is equivalent to the 65C22N and the W65C22N seems to be compatible with the rockwell.

I found this: https://www.mouser.co.uk/ProductDetail/955-W65C22N6TPG-14

Does anybody know if this is going to work for me?

Cheers!
 
Last edited:

stepleton

Well-known member
I'm afraid I don't know where to get a new IC --- my VIA was scavenged from a friend's battery-bombed Classic.

If your 'scope investigation shows that the data going from the ADB chip to the VIA has the correct keyboard scan codes, then replacing the VIA sounds like a reasonable idea to me.

That said, I'd be sure to measure this at the VIA itself. I don't know, but maybe a broken trace between the ADB chip and the VIA could cause the problem you're seeing.

Good luck!
 

tony359

Member
I've found this amazing video
and the author has the chip I found on the BOM which can be found here https://docs.google.com/document/d/1QhHpDew4saFxvt82W2TkdpnNA2W7tLZhe53Et64gpdY/edit.

So it seems the answer is yes.

BTW, I am based in the UK, if someone needs some of those VIA chips, please do let me know as I have to pay for shipment from the US anyways, maybe we could split! :)

Your point of probing the output of the ADB (or input of VIA of course) is actually a good idea. Difficult with a mouse but easier with a keyboard as I can set exactly the output code by pressing only once. Or I guess I could click the mouse to avoid the stream of data coming from movement.

I shall take a look indeed, thanks for the good idea. Might save me some money if I don't see the correct scan code there.
 

tony359

Member
I've spoiled the ending a bit here but here is part 1 of my repair. I trust this is not in violation of the rules of this forum.

Also please note what I said at the beginning of the video: this is my first Macintosh so please excuse my ignorance on how I approached the repair! :)

 

mdeverhart

Well-known member
Great video! You did a great job explaining everything, and I’m impressed how far you got given that you’re new to these old Macs. I’m looking forward to seeing Part 2!
 

tony359

Member
Thanks for letting me know! I'll try and complete the edit by the end of the week! :) Any feedback is always welcome!
 
Top