68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
Quadra 950 Keyboard/ADB issue
Posted by: superseth on 2025-04-11 14:02:21 Hello! I recently got some parts Q950's that I am trying to combine into a working machine. I was able to get one logic board booting (though the screen was green like what happened to action retro in a video I saw) but there is no keyboard input - AND YET the lock is in the \| position! I do not have any keys but I do have 2 locks, both technically open, and they both result in blocked keyboard input. Is there another fault area I should be checking? I can't find a lot of info about what pins to short to ensure it is always ON fully or if there are other logic board problems that could be resulting in this issue. I will say I am turning it on using the power button on the keyboard so I know SOMETHING is working on the ADB port.
Posted by: Byrd on 2025-04-11 22:55:16 I think you can jumper the motherboard to where the lock goes to bypass this; are you sure the good motherboard is functional noting the green screen issue?
Posted by: superseth on 2025-04-11 23:02:29 I am not certain no - but I did get it to boot into a 7.1 desktop just fine, but I couldn't do any input to test further, so things seem to MOSTLY be working. There are 3 pins on the logic board that the switch connects to - does anyone know what each does? It feels like a simple jumper should clear up if the issue is the board or the lock. Assuming it is the board, I wonder what controls the ADB lockout? Could there be a way to bypass it further down the line?
Posted by: cheesestraws on 2025-04-11 23:36:03 Have you checked whether the ADB fuse has blown?
Posted by: superseth on 2025-04-12 13:41:31 Where is that located? would the keyboard power button still work?
Posted by: cheesestraws on 2025-04-12 14:50:21 Where is that located? Can't remember, look for something labelled 'F' near the ADB ports. would the keyboard power button still work? Pretty sure yes: the power control line is on its own dedicated pin on the connector which the power button just pulls down to ground. It doesn't rely on the ADB device getting power.
Posted by: David Cook on 2025-04-12 15:04:33 For a quick check, measure the voltage on the adb connector. If you have an oscilloscope, you can also watch for the Mac to poll the ADB devices on pin 1. That should give you a sense for whether the keyboard/mouse lockout is software or a circuit problem.
Posted by: David Cook on 2025-04-12 17:25:26 BTW: If it is the keylock, then the floppy drive won't work either. So, you could always toss a disk in and see if it reads and shows up on the desktop. If it does, then ADB is the problem.
Posted by: superseth on 2025-04-12 19:51:23 Thank you so much for the detailed information - so based on this something is clearly wrong. I am getting 4.5v on my multimeter out of pin 1 and almost nothing/nothing on pin 4. as to the fuse...perhaps someone has stolen it?(If F4 is supposed to have a little fuse thing?)
Posted by: David Cook on 2025-04-12 20:31:40 Well, I have good news and bad news. The good news is that your F4 is not blown. The bad news is that your F4 fell off. If you're feeling bold, you could short the fuse or put a penny in there. I have a box of modern polyswitch/PPTC fuses. I would simply solder in something with around 1 amp trip (that was what prior Macintosh computers used). That area on your PCB does not look damaged. I assume the fuse simply hadn't been soldered well. am getting 4.5v on my multimeter out of pin 1 The data line is pulled up by a 470 ohm resistor. So, that makes sense.
Posted by: David Cook on 2025-04-12 20:42:01 Aside: I love how @cheesestraws guessed correctly immediately.
Posted by: superseth on 2025-04-12 22:36:45 Thanks for the info! I have a bombed 630 board around that I can probably get a fuse off. Otherwise I'll order one and see how it goes
Posted by: cheesestraws on 2025-04-12 23:45:19 Thanks for the info! I have a bombed 630 board around that I can probably get a fuse off. Yeah, this kind of thing is where I'd try to get one from too. Sounds sensible. Aside: I love how @cheesestraws guessed correctly immediately. A blown fuse is about my level of difficulty ;-) None of this semiconductor stuff, that sounds difficult...
Posted by: robin-fo on 2025-04-13 02:34:55 I have a bombed 630 board around that I can probably get a fuse off These can be tricky to desolder since they can separate when exposed to heat. Best buy new ones.
Posted by: cheesestraws on 2025-04-13 02:38:33 These can be tricky to desolder since they can separate when exposed to heat. Best buy new ones. ... that's a very good point that I didn't think of. I retract my statement that blown fuses are at my level of difficulty ;-)
Posted by: croissantking on 2025-04-13 13:28:21 These can be tricky to desolder since they can separate when exposed to heat. Best buy new ones. I’ve not once been able to successfully desolder that type of fuse, they always fall apart.
Posted by: finkmac on 2025-04-13 16:01:02 agree. they're very sensitive to heat. this is what you want.
Posted by: superseth on 2025-04-13 21:26:08 I am only an expert in filling my garage and office with broken old computers.
Posted by: superseth on 2025-04-18 15:45:16 Just wanted to report back that yes - replacing the missing fuse with SMD125F-2 as finkmac noted fixed my ADB!
Posted by: cheesestraws on 2025-04-18 15:47:33 That's good news!
1 >