Mac 128K Mouse Issue - Need Help

[WillJac]

I have a Mac 128K original, not modified in any way, that I just fixed and is booting up and all. The mouse works with movement but the button will not do anything. I know the mouse is good as I use it on another machine. I have tested the DB9 port, the RC pack is good, and no trace damages found. I see the mouse signal going into pin 14 on the 6522-chip high when not clicked and low when clicked. After this, I am lost not sure where it goes and what happens, but the click will not open anything on the screen. Anyone have any ideas on this and where I can go to solve it?

Thanks

 

[Phipli]

I'd check if the 6522 is generating an interrupt for the click (IRQ... pin 21 on the DIP part? Not sure what package it is on the 128). If it isn't, try replacing the 6522.

Does the signal make it all the way to Pin 14 (testing on the Pin not the pad)?

 

[WillJac]

I'd check if the 6522 is generating an interrupt for the click (IRQ... pin 21 on the DIP part? Not sure what package it is on the 128). If it isn't, try replacing the 6522.

Does the signal make it all the way to Pin 14 (testing on the Pin not the pad)?

Thanks for the reply. Yes, the single is all the way to the top of the pin 14 that goes low when button is pushed so it is getting into the 6522. The package is a 40 pin DIP so pin 21 is the IRQ. The single on 21 is high with dips to low but these dips are spaced out and when pressing button, really no big change. Now and then I might see a dip between the 2 normal once. I do have a donor plus board that has a 6522 on it that I can swap with. The only thing is the 6522 on the 128K board is the one with the fault so a resistor pack is added to a few pins. The 6522 on the plus has this issue resolved so would not need the resistor pack.

 

[WillJac]

An update on this:

I removed the 6522 from the 128K board and the resistor pack that is on pin 38, 37, 36, 35. Installed a socket (good quality machine type). Removed the 6522 from a donor plus board and tried it. Same thing. Installed the resistor pack on the bottom of the board and tried again, same thing. At first I did not use the resistor pack as the newer versions of the 6522 that the plus used did not need that as the defect in the chip was fixed. I put the original chip back in the socket and all is still the same. No click. I do see it coming in on pin 13 but after that I don't know what happens with it.

I don't know enough about the 6522 to determine what happens on the inside of it and how/where the single should be coming out and where it goes after. Anyone have ideas or input on this?

Thanks

 

[Phipli]

Have you downloaded the schematics? I'd be checking the address lines to make sure they're properly connected to the 6522 enable and address pins. What other peripherals are connected to the same 6522? Is the computer not able to talk to it?

 

[WillJac]

Have you downloaded the schematics? I'd be checking the address lines to make sure they're properly connected to the 6522 enable and address pins. What other peripherals are connected to the same 6522? Is the computer not able to talk to it?

I have the schematics and using it heavily. The 6522 handles the other ports, talked with the rtc and iwm and all that is working. The mouse moves and that also comes from the 6522 via chip. Address lines are checked and seem fine to me. Compared to another machine is identical.

 

[Phipli]

You've sort of said that everything downstream of the VIA is ok, the VIA is ok, and that everything upstream of the VIA is ok. That's a little confusing, which I guess is why you're asking.

Have you booted from a different disk to make sure it isn't software? If you have, then the problem might still exists somewhere you have already tested. Are the signal voltages from the mouse right? Is it generating a strong signal that meets the voltage requirements for logic high and logic low of the VIA?

Don't most macs have two VIAs? Is all that hardware you mentioned really connected to the same one? Forgive me, I don't have a 128.

Edit - checked a photo - one VIA. Its doing a lot of work

 

[WillJac]

You've sort of said that everything downstream of the VIA is ok, the VIA is ok, and that everything upstream of the VIA is ok. That's a little confusing, which I guess is why you're asking.

Have you booted from a different disk to make sure it isn't software? If you have, then the problem might still exists somewhere you have already tested. Are the signal voltages from the mouse right? Is it generating a strong signal that meets the voltage requirements for logic high and logic low of the VIA?

Don't most macs have two VIAs? Is all that hardware you mentioned really connected to the same one? Forgive me, I don't have a 128.

Edit - checked a photo - one VIA. Its doing a lot of work

OMG what you said I never thought about. The voltage level coming to the via pin 13 for the mouse click. This can very well be the issue where it is not being pulled down enough to trigger.

Not even checking the level, I went ahead and changed the resister pack and DANG! it now works. So yes, the voltage level was the issue.

One via only and yes it does a lot of work but then this machine not have much on it either.

I can now put this machine in the done/restored category and THANK YOU for your input and help. You can watch my work and the repairs on this on my channel at CayMac Vintage.

Thanks again.

 

[Phipli]

OMG what you said I never thought about. The voltage level coming to the via pin 13 for the mouse click. This can very well be the issue where it is not being pulled down enough to trigger.

Not even checking the level, I went ahead and changed the resister pack and DANG! it now works. So yes, the voltage level was the issue.

One via only and yes it does a lot of work but then this machine not have much on it either.

I can now put this machine in the done/restored category and THANK YOU for your input and help. You can watch my work and the repairs on this on my channel at CayMac Vintage.

Thanks again.

Glad its sorted awesome work.